2.2. The history of the creation of the Periodic system.
In the winter of 1867-68, Mendeleev began to write the textbook "Fundamentals of Chemistry" and immediately encountered difficulties in systematizing the factual material. By mid-February 1869, while pondering the structure of the textbook, he gradually came to the conclusion that the properties of simple substances (and this is the form of the existence of chemical elements in a free state) and the atomic masses of elements are connected by a certain pattern.
Mendeleev did not know much about the attempts of his predecessors to arrange the chemical elements in order of increasing atomic masses and about the incidents that arose in this case. For example, he had almost no information about the work of Chancourtois, Newlands, and Meyer.
The decisive stage of his thoughts came on March 1, 1869 (February 14, old style). A day earlier, Mendeleev wrote a request for a ten-day vacation to inspect artel cheese factories in the Tver province: he received a letter with recommendations for studying cheese production from A. I. Khodnev, one of the leaders of the Free Economic Society.
Petersburg that day was cloudy and frosty. The trees creaked in the wind in the university garden, where the windows of Mendeleev's apartment looked out. While still in bed, Dmitry Ivanovich drank a mug of warm milk, then got up, washed himself and went to breakfast. His mood was wonderful.
At breakfast, Mendeleev had an unexpected idea: to compare close atomic masses of various chemical elements and their chemical properties. Without thinking twice, on the reverse side of Khodnev's letter, he wrote down the symbols for chlorine Cl and potassium K with fairly similar atomic masses, equal to 35.5 and 39, respectively (the difference is only 3.5 units). In the same letter, Mendeleev sketched symbols of other elements, looking for similar "paradoxical" pairs among them: fluorine F and sodium Na, bromine Br and rubidium Rb, iodine I and cesium Cs, for which the mass difference increases from 4.0 to 5.0 and then to 6.0. Mendeleev then could not know that the "indefinite zone" between obvious non-metals and metals contains elements - noble gases, the discovery of which in the future will significantly modify the Periodic Table.
After breakfast, Mendeleev closed himself in his office. He took out a pack of business cards from the desk and began to write the symbols of the elements and their main chemical properties on their reverse side. After a while, the household heard how it began to be heard from the office: "Uuu! Horned one. Wow, what a horned one! I will overcome them. I will kill them!" These exclamations meant that Dmitry Ivanovich had a creative inspiration. Mendeleev shifted the cards from one horizontal row to another, guided by the values of the atomic mass and the properties of simple substances formed by atoms of the same element. Once again, a thorough knowledge of inorganic chemistry came to his aid. Gradually, the appearance of the future Periodic Table of chemical elements began to take shape. So, at first he put a card with the element beryllium Be (atomic mass 14) next to the card of the aluminum element Al (atomic mass 27.4), according to the then tradition, taking beryllium for an analogue of aluminum. However, then, comparing the chemical properties, he placed beryllium over magnesium Mg. Having doubted the then generally accepted value of the atomic mass of beryllium, he changed it to 9.4, and changed the formula of beryllium oxide from Be 2 O 3 to BeO (like magnesium oxide MgO). By the way, the "corrected" value of the atomic mass of beryllium was confirmed only ten years later. He acted just as boldly on other occasions.
Gradually, Dmitry Ivanovich came to the final conclusion that the elements, arranged in ascending order of their atomic masses, show a clear periodicity in physical and chemical properties. Throughout the day, Mendeleev worked on the system of elements, taking short breaks to play with his daughter Olga, have lunch and dinner.
On the evening of March 1, 1869, he whitewashed the table he had compiled and, under the title "Experiment of a system of elements based on their atomic weight and chemical similarity," sent it to the printer, making notes for typesetters and putting the date "February 17, 1869" (this is according to the old style).
Thus, the Periodic Law was discovered, the modern formulation of which is as follows: The properties of simple substances, as well as the forms and properties of compounds of elements, are in a periodic dependence on the charge of the nuclei of their atoms.
Mendeleev sent printed sheets with a table of elements to many domestic and foreign chemists, and only after that he left St. Petersburg to inspect cheese factories.
Before his departure, he still managed to hand over to N. A. Menshutkin, an organic chemist and future historian of chemistry, the manuscript of the article "Relationship of properties with the atomic weight of elements" - for publication in the Journal of the Russian Chemical Society and for communication at the upcoming meeting of the society.
On March 18, 1869, Menshutkin, who at that time was the clerk of the society, made a small report on the Periodic Law on behalf of Mendeleev. The report at first did not attract much attention of chemists, and the President of the Russian Chemical Society, Academician Nikolai Zinin (1812-1880) stated that Mendeleev was not doing what a real researcher should do. True, two years later, after reading Dmitry Ivanovich's article "The natural system of elements and its application to indicating the properties of certain elements," Zinin changed his mind and wrote to Mendeleev: "Very, very good, very excellent approximations, even fun to read, God bless you good luck in experimental confirmation of your conclusions. Sincerely devoted to you and deeply respecting you N. Zinin. Mendeleev did not place all the elements in ascending order of atomic masses; in some cases he was more guided by the similarity of chemical properties. So, cobalt Co has an atomic mass greater than nickel Ni, tellurium Te also has a greater mass than iodine I, but Mendeleev placed them in the order Co - Ni, Te - I, and not vice versa. Otherwise, tellurium would fall into the group of halogens, and iodine would become a relative of selenium Se.
To his wife and children. Or maybe he knew that he was dying, but did not want to disturb and excite the family in advance, whom he loved passionately and tenderly. At 5:20 a.m. January 20, 1907 Dmitry Ivanovich Mendeleev died. He was buried at the Volkovsky cemetery in St. Petersburg, not far from the graves of his mother and son Vladimir. In 1911, the Museum of D.I. Mendeleev, where ...
Moscow metro station, research ship for oceanographic research, 101st chemical element and mineral - mendeleevite. Russian-speaking scientists-jokers sometimes ask: "Isn't Dmitry Ivanovich Mendeleev a Jew, a painfully strange surname, didn't it come from the surname "Mendel"?" The answer to this question is extremely simple: "All four sons of Pavel Maksimovich Sokolov, ...
Lyceum exam, where old Derzhavin blessed the young Pushkin. The role of the meter happened to be played by Academician Yu.F. Fritsshe, a well-known specialist in organic chemistry. PhD thesis D.I. Mendeleev graduated from the Main Pedagogical Institute in 1855. PhD thesis "Isomorphism in connection with other relationships of crystalline form to composition" became his first major scientific ...
Mostly on the issue of capillarity and surface tension of liquids, and he spent his leisure time in the circle of young Russian scientists: S.P. Botkin, I.M. Sechenov, I.A. Vyshnegradsky, A.P. Borodina and others. In 1861, Mendeleev returned to St. Petersburg, where he resumed lecturing on organic chemistry at the university and published a textbook, remarkable for that time: "Organic Chemistry", in ...
In the book of the prominent Soviet historian of chemistry N.F. Figurovsky "Essay on the General History of Chemistry. The Development of Classical Chemistry in the 19th Century" (M., Nauka, 1979). the main periods of the discovery of 63 chemical elements from ancient times to 1869 - the year of the establishment by Dmitry Ivanovich Mendeleev (1834-1907) of the Periodic Law are given:
1. The most ancient period (from the 5th millennium BC to 1200 AD).
This long period includes the acquaintance of a person with 7 metals of antiquity - gold, silver, copper, lead, tin, iron and mercury. In addition to these elementary substances, sulfur and carbon were known in antiquity, occurring in nature in a free state.
2. Alchemical period.
During this period (from 1200 to 1600), the existence of several elements was established, isolated either in the process of alchemical searches for ways to transmute metals, or in the processes of metal production and processing of various ores by artisan metallurgists. These include arsenic, antimony, bismuth, zinc, phosphorus.
3. The period of emergence and development of technical chemistry (end of the 17th century - 1751).
At that time, as a result of a practical study of the characteristics of various metal ores and overcoming the difficulties that arose in the isolation of metals, as well as discoveries in the process of mineralogical expeditions, the existence of platinum, cobalt, and nickel was established.
4. The first stage of the chemical-analytical period in the development of chemistry (1760-1805). During this period, with the help of qualitative and weight quantitative analyzes, a number of elements were discovered, some of them only in the form of "earths": magnesium, calcium (establishing the difference between lime and magnesia), manganese, barium (barite), molybdenum, tungsten, tellurium, uranium (oxide), zirconium (earth), strontium (earth), titanium (oxide), chromium, beryllium (oxide), yttrium (earth), tantalum (earth), cerium (earth), fluorine (hydrofluoric acid), palladium, rhodium, osmium and iridium.
5. Stage of pneumatic chemistry. At this time (1760-1780), gaseous elements were discovered - hydrogen, nitrogen, oxygen and chlorine (the latter was considered a complex substance - oxidized hydrochloric acid until 1809).
6. The stage of obtaining elements in a free state by electrolysis (G. Davy, 1807-1808) and chemically: potassium, sodium, calcium, strontium, barium and magnesium. All of them, however, were previously known in the form of "flammable" (caustic) alkalis and alkaline earths, or soft alkalis.
7. The second stage of the chemical-analytical period in the development of chemistry (1805-1850). At this time, as a result of improving the methods of quantitative analysis and developing a systematic course of qualitative analysis, boron, lithium, cadmium, selenium, silicon, bromine, aluminum, iodine, thorium, vanadium, lanthanum (earth), erbium (earth), terbium (earth) were discovered. ), ruthenium, niobium.
8. The period of discovery of elements by means of spectral analysis, immediately following the development and introduction of this method into practice (1860-1863): cesium, rubidium, thallium and indium.
As you know, the first in the history of chemistry "Table of Simple Bodies" was compiled by A. Lavoisier in 1787. All simple substances were divided into four groups: "I. Simple substances presented in all three kingdoms of nature, which can be considered as elements of bodies: 1) light, 2) caloric, 3) oxygen, 4) nitrogen, 5) hydrogen II.Simple non-metallic substances that oxidize and give acids: 1) antimony, 2) phosphorus, 3) coal, 4) muriatic acid radical, 5 ) hydrofluoric acid radical, 6) boric acid radical III.Simple metal substances that are oxidized and give acids: 1) antimony, 2) silver, 3) arsenic, 4) bismuth, 5) cobalt, 6) copper, 7) tin, 8) iron, 9) manganese, 10) mercury, 11) molybdenum, 12) nickel, 13) gold, 14) platinum, 15) lead, 16) tungsten, 17) zinc IV. ) lime (calcareous earth), 2) magnesia (magnesium sulfate base), 3) barite (heavy earth), 4) alumina (clay, alum earth), 5) silica (siliceous earth)".
This table formed the basis of the chemical nomenclature developed by Lavoisier. D. Dalton introduced into science the most important quantitative characteristic of atoms of chemical elements - the relative weight of atoms or atomic weight.
When searching for regularities in the properties of atoms of chemical elements, scientists first of all paid attention to the nature of the change in atomic weights. In 1815-1816. the English chemist W. Prout (1785-1850) published two anonymous articles in the Annals of Philosophy, in which the idea was expressed and substantiated that the atomic weights of all chemical elements are integer (i.e., multiples of the atomic weight of hydrogen, which was then taken equal to unit): "If the views that we have decided to express are correct, then we can almost consider that the primordial matter of the ancients is embodied in hydrogen ...". Prout's hypothesis was very tempting and led to the setting up of many experimental studies in order to determine the atomic weights of chemical elements as accurately as possible.
In 1829, the German chemist I. Debereiner (1780-1849) compared the atomic weights of similar chemical elements: Lithium, Calcium, Chlorine, Sulfur, Manganese, Sodium, Strontium, Bromine, Selenium, Chromium, Potassium, Barium, Iodine, Tellurium, Iron and found that the atomic weight of the middle element is equal to half the sum of the atomic weights of the extreme elements. The search for new triads led L. Gmelin (1788-1853), the author of the world-famous reference guide to chemistry, to the establishment of numerous groups of similar elements and to the creation of their peculiar classification.
In the 60s. In the 19th century, scientists switched to comparing the groups of chemically similar elements themselves. Thus, A. Shancourtois (1820-1886), a professor at the Paris Mining School, arranged all the chemical elements on the surface of a cylinder in ascending order of their atomic weights so that a "helix" was obtained. With this arrangement, similar elements often fell on the same vertical line. In 1865, the English chemist D. Newlands (1838-1898) published a table that included 62 chemical elements. The elements were arranged and numbered in ascending order of atomic weights.
Newlands used numbering to emphasize that every seven elements, the properties of chemical elements are repeated. When discussing in the London Chemical Society in 1866 a new article by Newlands (it was not recommended for publication), Professor J. Foster asked sarcastically: “Have you tried to arrange the elements in alphabetical order of their names and have you noticed any new patterns?
In 1868, the English chemist W. Olding (1829-1921) proposed a table, which, in the author's opinion, demonstrated a regular relationship between all elements.
In 1864, the German professor L. Mayer (1830-1895) compiled a table of 44 chemical elements (out of 63 known).
Assessing this period, D.I. Mendeleev wrote "There is not a single general law of nature that would be based immediately, its approval is always preceded by many forebodings, and the recognition of the law does not come when it is fully realized in all its meaning, but only after the confirmation of its consequences by experiments, which natural scientists must recognize as the highest authority of their considerations and opinions.
In 1868 D.I.Mendeleev began to work on the course "Fundamentals of Chemistry". For the most logical arrangement of the material, it was necessary to somehow classify 63 chemical elements. The first version of the Periodic Table of Chemical Elements was proposed by D.I. Mendeleev in March 1869.
Two weeks later, at a meeting of the Russian Chemical Society, Mendeleev's report "The relationship of properties with the atomic weight of elements" was read out, in which possible principles for the classification of chemical elements were discussed:
1) according to their relation to hydrogen (formulas of hydrides); 2) according to their relation to oxygen (formulas of higher oxygen oxides); 3) by valency; 4) in terms of atomic weight.
Further, during the following years (1869-1871), Mendeleev studied and rechecked those regularities and "inconsistencies" that were noticed in the first version of the "System of Elements". Summing up this work, D.I. Mendeleev wrote: "As the atomic weight increases, the elements first have more and more changeable properties, and then these properties are repeated again in a new order, in a new line and in a number of elements and in the same sequence Therefore, the Law of Periodicity can be formulated as follows: "The properties of the elements, and therefore the properties of the simple and complex bodies they form, are in a periodic dependence (that is, they repeat correctly) on their atomic weight." nature of exceptions are not tolerated... The affirmation of a law is possible only with the help of deriving consequences from it, which are impossible and unexpected without it, and the justification of those consequences and experimental verification. there are such logical consequences that could show whether it is true or not.These include the prediction of the properties of undiscovered elements and the correction of the atomic weights of many, few studied elements at that time ... One must do one thing - or consider the periodic law to be true to the end and constituting a new instrument of chemical knowledge, or reject it."
During 1872-1874. Mendeleev began to deal with other problems, and there was almost no mention of the Periodic Law in the chemical literature.
In 1875, the French chemist L. de Boisbaudran reported that while studying zinc blende, he spectroscopically discovered a new element in it. He received the salts of this element and determined its properties. In honor of France, he named the new element gallium (as France was called by the ancient Romans). Let's compare what D.I. Mendeleev predicted and what was found by L. de Boisbaudran:
In the first report by L. de Boisbaudran, the specific gravity of gallium was found to be 4.7. DIMendeleev pointed out to him his mistake. A more careful measurement showed that the specific gravity of gallium was 5.96.
In 1879, the Swedish chemist L. Nilsson (1840-1899) reported on the discovery of a new chemical element - scandium. L. Nilson classified scandium as a rare earth element. P.T.Kleve pointed out to L.Nilson that scandium salts are colorless, its oxide is insoluble in alkalis, and that scandium is ekabor predicted by D.I.Mendeleev. Let's compare their properties.
Analyzing a new mineral in February 1886, German professor K. Winkler (1838-1904) discovered a new element and considered it an analogue of antimony and arsenic. There was a discussion. K. Winkler agreed that the element he had discovered was the ecasilicon predicted by D. I. Mendeleev. K. Winkler called this element germanium.
So, chemists confirmed the existence of the chemical elements predicted by Mendeleev three times. Moreover, it was precisely the properties of these elements predicted by Mendeleev and their position in the Periodic system that made it possible to correct the errors that experimenters unwittingly made. The further development of chemistry took place on a solid basis of the Periodic Law, which in the 80s of the XIX century. was recognized by all scientists as one of the most important laws of nature. Thus, the most important characteristic of any chemical element is its place in the Periodic system of D.I. Mendeleev.
The Mendeleev family lived in a house on the steep high bank of the Tobol River in the city of Tobolsk, and the future scientist was born here. At that time, many Decembrists were serving exile in Tobolsk: Annenkov, Baryatinsky, Wolf, Kuchelbecker, Fonwiesen and others ... They infected others with their courage and hard work. They were not broken by prisons, hard labor, or exile. Mitya Mendeleev saw such people. In communication with them, his love for the Motherland, responsibility for its future was formed. The Mendeleev family was on friendly and family terms with the Decembrists. D. I. Mendeleev wrote: “... respectable and respected Decembrists lived here: Fonvizen, Annenkov, Muravyov, close to our family, especially after one of the Decembrists, Nikolai Vasilyevich Basargin, married my sister Olga Ivanovna ... Decembrist families , in those days they gave Tobolsk life a special imprint, endowed it with a secular education. The legend about them still lives in Tobolsk.
At the age of 15, Dmitry Ivanovich graduated from the gymnasium. His mother Maria Dmitrievna made a lot of efforts for the young man to continue his education.
Rice. 4. Mother of D. I. Mendeleev - Maria Dmitrievna.
Mendeleev tried to enter the Medical-Surgical Academy in St. Petersburg. However, anatomy was beyond the power of an impressionable young man, so Mendeleev had to change medicine to pedagogy. In 1850, he entered the Main Pedagogical Institute, where his father had once studied. Only here Mendeleev felt a taste for study and soon became one of the best.
At the age of 21, Mendeleev brilliantly passed the entrance exams. The study of Dmitri Mendeleev in St. Petersburg at the Pedagogical Institute was not easy at first. In his first year, he managed to get unsatisfactory grades in all subjects except mathematics. But in senior years, things went differently - Mendeleev's average annual score was four and a half (out of five possible).
His thesis on the phenomenon of isomorphism was recognized as a PhD thesis. A talented student in 1855. was appointed teacher at the Richelieu Gymnasium in Odessa. Here he prepared the second scientific work - "Specific volumes". This work was presented as a master's thesis. In 1857 after her defense, Mendeleev received the title of Master of Chemistry, became assistant professor at St. Petersburg University, where he lectured on organic chemistry. In 1859 he was sent abroad.
Mendeleev spent two years at various universities in France and Germany, but his dissertation work in Heidelberg with the leading scientists of that time, Bunsen and Kirchhoff, was the most productive.
Undoubtedly, the nature of the environment in which he spent his childhood greatly influenced the scientist's life. From his youth to his old age, he did everything and always in his own way. Starting with the little things and moving on to the big things. The niece of Dmitry Ivanovich, N. Ya. Kapustina-Gubkina, recalled: “He had his favorite dishes, invented by him for himself ... He always wore a wide cloth jacket without a belt of his own design ... He smoked twisted cigarettes, rolling them himself ... ". He created an exemplary estate - and immediately abandoned it. He conducted remarkable experiments on the adhesion of liquids, and immediately left this field of science forever. And what scandals he rolled up to the authorities! Even in his youth, a fledgling graduate of the Pedagogical Institute, he yelled at the director of the department, for which he was called to the minister Abraham Sergeevich Norovatov himself. However, what is the director of the department to him - he did not even reckon with the synod. When he imposed on him a seven-year penance on the occasion of a divorce from Feoza Nikitishna, who never reconciled herself to the peculiarity of his interests, Dmitry Ivanovich, six years before the due date, persuaded the priest in Kronstadt to marry him again. And what was the story of his balloon flight worth when he seized by force a balloon belonging to the military department, driving General Kovanko, an experienced aeronaut, out of the basket ... Dmitry Ivanovich did not suffer from modesty, on the contrary - “Modesty is the mother of all vices,” Mendeleev argued.
The originality of the personality of Dmitry Ivanovich was observed not only in the behavior of the scientist, but also in his whole appearance. His niece N. Ya. Kapustina-Gubkina drew the following verbal portrait of the scientist: “A mane of long fluffy hair around a high white forehead, very expressive and very mobile ... Clear blue, penetrating eyes ... In him, many found similarities with Garibaldi ... When talking, he always gesticulated . Wide, quick, nervous movements of his hands always corresponded to his mood ... The timbre of his voice was low, but sonorous and intelligible, but his tone changed very much and often switched from low notes to high, almost tenor ones ... When he spoke about what he did not like , then frowned, bent down, groaned, squeaked ... ". Mendeleev's favorite pastime for many years was the manufacture of suitcases and frames for portraits. He bought supplies for these works in Gostiny Dvor.
Mendeleev's originality distinguished him from the general mass from his youth ... While studying at the Pedagogical Institute, the blue-eyed Siberian, who did not have a penny for his soul, unexpectedly for gentlemen professors, began to show such sharpness of mind, such fury in work, that he left far behind all his comrades. It was then that he was noticed and loved by a real state councilor, a well-known figure in public education, a teacher, scientist, professor of chemistry Alexander Abramovich Voskresensky. Therefore, in 1867, Alexander Abramovich recommended his favorite student, thirty-three-year-old Dmitry Ivanovich Mendeleev, to the post of professor of general and inorganic chemistry at the Faculty of Physics and Mathematics at St. Petersburg University. In May 1868, the beloved daughter Olga was born to the Mendeleevs ...
Thirty-three is the traditional age of a feat: at thirty-three, according to the epic of tears from the stove, Ilya Muromets. But although in this sense the life of Dmitry Ivanovich was no exception, he himself could hardly feel that a sharp turn was taking place in his life. Instead of the courses in technical, or organic, or analytical chemistry he had taught earlier, he had to start reading a new course, general chemistry.
Of course, the knurled easier. However, when he started his former courses, it was also not easy. Russian benefits either did not exist at all, or they existed, but they were outdated. Chemistry is a new, young thing, and in youth everything becomes outdated quickly. Foreign textbooks, the latest ones, had to be translated by myself. He translated - "Analytical Chemistry" by Gerard, "Chemical Technology" by Wagner. And in organic chemistry and in Europe nothing worthy was found, even though you sit down and write yourself. And wrote. In two months, a completely new course based on new principles, thirty printed sheets. Sixty days of daily hard labor - twelve finished pages a day. It was on a day - he did not want to set his routine depending on such a trifle as the rotation of the globe around its axis, he did not get up from the table for thirty or forty hours.
Dmitry Ivanovich could not only work drunkenly, but also sleep drunkenly. Mendeleev's nervous system was extremely sensitive, his senses were sharpened - almost all memoirists, without saying a word, report that he was unusually easy, constantly broke into a cry, although, in essence, he was a kind person.
It is possible that the innate personality traits of Dmitry Ivanovich were explained by his late appearance in the family - he was the "last child", the seventeenth child in a row. And according to current ideas, the possibility of mutations in offspring increases with increasing age of the parents.
He began his first lecture on general chemistry as follows:
“Everything we notice, we clearly distinguish as a substance, or as a phenomenon. Matter occupies space and has weight, while phenomena are things that happen in time. Each substance exerts a variety of phenomena, and there is not a single phenomenon that takes place without substance. A variety of substances and phenomena cannot escape the attention of everyone. To discover legitimacy, that is, simplicity and regularity in this diversity, means to study nature ... "
To discover legitimacy, that is, simplicity, and correctness… Substance has weight… Substance… Weight… Substance… Weight…
He thought about it all the time, no matter what he did. And what did he not do! Dmitry Ivanovich had enough time for everything. It would seem that he finally received the best chemical department in Russia, a state-owned apartment, the opportunity to live comfortably, without running around for extra money - so focus on the main thing, and everything else is on the side ... I bought an estate of 400 acres of land and a year later laid experienced floor, on which he studied the possibility of reversing the depletion of the earth with the help of chemistry. One of the first in Russia.
A year and a half has passed like an instant, but there was still no real system in general chemistry. This does not mean that Mendeleev read his course quite haphazardly. He began with what is familiar to everyone - from water, from air, from coal, from salts. From the elements they contain. From the main laws, according to which substances interact with each other.
Then he spoke about the chemical relatives of chlorine - fluorine, bromine, iodine. This was the last lecture, the transcript of which he still managed to send to the printing house, where the second edition of the new book he had started was typed.
The first issue, in pocket format, was printed in January 1869. The title page read: "Fundamentals of Chemistry D. Mendeleev" . No preface. The first, already published issue, and the second, which was in the printing house, were supposed to be, according to Dmitry Ivanovich, the first part of the course, and two more issues - the second part.
In January and the first half of February, Mendeleev gave lectures on sodium and other alkali metals, wrote the corresponding chapter of the second part. "Fundamentals of Chemistry" - and stuck.
In 1826, Jens Jakob Berzelius completed the study of 2000 substances and, on this basis, the determination of the atomic weight of three dozen chemical elements. Five of them had incorrect atomic weights—sodium, potassium, silver, boron, and silicon. Berzelius was wrong because he made two incorrect assumptions: that there can be only one metal atom in an oxide molecule, and that an equal volume of gases contains an equal number of atoms. In fact, an oxide molecule can contain two or more metal atoms, and an equal volume of gases, according to Avogadro's law, contains an equal number of not atoms, but molecules.
Until 1858, when the Italian Stanislao Cannicaro, having reinstated the law of his compatriot Avogadro, corrected the atomic weights of several elements, confusion reigned in the matter of atomic weights.
Only in 1860, at the chemical congress in Karlsruhe, after heated debate, the confusion was unraveled, Avogadro's law was finally restored in its rights, and finally unshakable foundations for determining the atomic weight of any chemical element were clarified.
By a happy coincidence, Mendeleev was on a business trip abroad in 1860, attended this congress and received a clear and distinct idea that atomic weight has now become an accurate and reliable numerical expression. Returning to Russia, Mendeleev began to study the list of elements, and drew attention to the periodicity of the change in valency for elements arranged in ascending order of atomic weights: valence H – 1, Li – 1, Be – 2, B - 3, C - 4, mg – 2, N – 2, S - 2, F - 1, Na – 1, Al – 3, Si - 4, etc. Based on the increase and decrease in valency, Mendeleev broke down the elements into periods; The 1st period included only one hydrogen, followed by two periods of 7 elements each, then periods containing more than 7 elements. D, I, Mendeleev used these data not only to build a graph, as did Meyer and Chancourtua, but also to build a table similar to the Newlands table. Such a periodic table of elements is clearer and more visual than a graph, and, in addition, D, I, Mendeleev managed to avoid the error of Newlands, who insisted on the equality of periods.
« I consider the 1860 congress of chemists in Karlsruhe, in which I participated, to be the decisive moment of my thought about the periodic law ... , - noted D.I. Mendeleev.
In 1865, he bought the Boblovo estate near Klin and got the opportunity to engage in agricultural chemistry, which he was then fond of, and relax there with his family every summer.
The “birthday” of D.I. Mendeleev’s system is usually considered February 18, 1869, when the first version of the table was compiled.
Rice. 5. Photo by D. I. Mendeleev in the year of the discovery of the periodic law.
63 chemical elements were known. Not all properties of these elements have been studied well enough, even the atomic weights of some have been determined incorrectly or inaccurately. Is it a lot or a little - 63 elements? If we remember that now we know 109 elements, then, of course, it is not enough. But it is quite enough to be able to notice the pattern of changes in their properties. With 30 or 40 known chemical elements, it would hardly be possible to discover anything. A certain minimum of open elements was needed. That is why one can characterize Mendeleev's discovery as timely.
Before Mendeleev, scientists also tried to subordinate all known elements to a certain order, to classify them, to bring them into a system. It is impossible to say that their attempts were useless: they contained some grains of truth. All of them limited themselves to uniting elements similar in chemical properties into groups, but did not find an internal connection between these "natural", as they said then, their groups.
In 1849, the prominent Russian chemist G. I. Hess became interested in the classification of elements. In the textbook Foundations of Pure Chemistry, he described four groups of non-metal elements with similar chemical properties:
I Te C N
Br Se B P
Cl S Si As
F O
Hess wrote: "This classification is still very far from being natural, but it still connects elements and groups that are very similar, and with the expansion of our information it can be improved."
Unsuccessful attempts to build a system of chemical elements based on their atomic weights were made even before the congress in Karlsruhe, both by the British: in 1853 by Gladstone, in 1857 by Odling.
One of the classification attempts was made in 1862 by the Frenchman Alexander Emile Beguis de Chancourtois . He represented the system of elements in the form of a spiral line on the surface of the cylinder. Each turn has 16 elements. Similar elements were located one below the other on the generatrix of the cylinder. When publishing his message, the scientist did not accompany it with the graph he built, and none of the scientists paid attention to the work of de Chancourtois.
Rice. 6. "Tellurium screw" de Chancourtua.
More successful was the German chemist Julius Lothar Meyer. In 1864, he proposed a table in which all known chemical elements were divided into six groups, according to their valency. In appearance, Meyer's table was a bit like the future Mendeleev's. He considered the volumes occupied by weight quantities of an element numerically equal to their atomic weights. It turned out that each such weight of any element contains the same number of atoms. This meant that the ratio of the considered volumes of various atoms of these elements. Therefore, the specified characteristic of the element is called atomic volume.
Graphically, the dependence of the atomic volumes of elements on their atomic weights is expressed as a series of waves rising in sharp peaks at points corresponding to alkali metals (sodium, potassium, cesium). Each descent and ascent to the peak corresponds to a period in the table of elements. In each period, the values of some physical characteristics, in addition to the atomic volume, also naturally decrease first and then increase.
Rice. 7. Dependence of atomic volumes on the atomic masses of elements, according to
L. Meyer.
Hydrogen, the element with the smallest atomic weight, was first on the list of elements. At that time, it was customary to assume that the 101st period includes one element. The 2nd and 3rd periods of the Meyer chart included seven elements each. These periods duplicated the Newlands octaves. However, in the next two periods, the number of elements exceeded seven. Thus, Meyer showed what Newlands' mistake was. The law of octaves could not be strictly observed for the entire list of elements, the last periods had to be longer than the first ones.
After 1860, another English chemist, John Alexander Reina Newlands, made the first attempt of this kind. One after another, he compiled tables in which he tried to translate his idea. The last table is dated 1865. The scientist believed that everything in the world is subject to general harmony. And in chemistry and in music it should be the same. Arranged in ascending order, the atomic weights of the elements are divided into octaves in it - into eight vertical rows, seven elements each. Indeed, many chemically related elements ended up in the same horizontal line: in the first - halogens, in the second - alkali metals, and so on. But, unfortunately, a lot of strangers also got into the ranks, and this spoiled the whole picture. Among the halogens, for example, there were cobalt with nickel and three platinoids. In the line of alkaline earths - vanadium and lead. The carbon family includes tungsten and mercury. In order to somehow combine related elements, Newlands had to violate the arrangement of elements in order of atomic weights in eight cases. In addition, in order to make eight groups of seven elements, 56 elements are needed, and 62 were known, and in some places he put two elements at once in place of one element. It turned out to be a complete mess. When Newlands reported his "The Law of Octaves" at a meeting of the London Chemical Society, one of those present sarcastically remarked: did the venerable speaker try to arrange the elements simply alphabetically and discover some regularity?
All these classifications did not contain the main thing: they did not reflect the general, fundamental pattern of changes in the properties of elements. They created only the appearance of order in their world.
Mendeleev's predecessors, who noticed particular manifestations of the great regularity in the world of chemical elements, for various reasons, could not rise to the great generalization and realize the existence of a fundamental law in the world. Mendeleev did not know much about the attempts of his predecessors to arrange the chemical elements in order of increasing atomic masses and about the incidents that arose in this case. For example, he had almost no information about the work of Chancourtois, Newlands, and Meyer.
Unlike Newlands, Mendeleev considered the main thing not so much atomic weights as chemical properties, chemical individuality. He thought about this all the time. Substance… Weight… Substance… Weight… No decisions came.
And then Dmitry Ivanovich got into a fierce time trouble. And it turned out quite badly: not that it was “now or never”, but either today, or the case was again postponed for several weeks.
Long ago he made a promise in the Free Economic Society that he would go to the Tver province in February, inspect the local cheese dairies and present his views on staging this matter in a modern way. The permission of the university authorities had already been requested for the trip. And the "vacation certificate" - the then travel certificate - had already been corrected. And the last parting note of the Secretary of the Free Economic Society Khodnev received. And there was nothing left but to go on the appointed voyage. The train, on which he was to travel to Tver, departed from the Moscow railway station on February 17, in the evening.
“In the morning, while still in bed, he invariably drank a mug of warm milk ... Getting up and washing himself, he immediately went to his office and drank one or two, sometimes three large, in the form of a mug, a cup of strong, not very sweet tea” (from the memoirs of his niece N.Ya. Kapustina-Gubkina).
The trace of the cup, preserved on the reverse side of Khodnev's note, dated February 17, indicates that it was received early in the morning, before breakfast, probably brought by messenger. And this, in turn, indicates that the thought of a system of elements did not leave Dmitry Ivanovich day or night: next to the imprint of a cup, a leaf keeps visible traces of an invisible thought process that led to a great scientific discovery. In the history of science, this is the rarest case, if not the only one.
Judging by the physical evidence, it happened like this. Having finished his mug and put it in the first place that came across - on Khodnev's letter, he immediately grabbed his pen and on the first piece of paper that came across, on the same Khodnev's letter, wrote down the thought that flashed through his head. On the sheet appeared, one under the other, the symbols of chlorine and potassium... Then sodium and boron, then lithium, barium, hydrogen... The pen wandered, as did the thought. Finally, he took a normal eighth of clean paper - this sheet also survived - and sketched on it, one under the other, in descending order, lines of symbols and atomic weights: alkaline earths above, below them halogens, below them an oxygen group, below it nitrogen, below it a group carbon, etc. It was obvious to the naked eye how close the differences in atomic weights are between the elements of neighboring ranks. Mendeleev then could not know that the "indefinite zone" between the obvious non-metals And metals contains elements - noble gases, the discovery of which in the future will significantly modify the Periodic Table.
He was in a hurry, so every now and then he made mistakes, made typos. Sulfur attributed the atomic weight of 36, instead of 32. Subtracting them 65 (the atomic weight of zinc) 39 (the atomic weight of potassium), got 27. But it's not about the little things! He was carried by a high wave of intuition.
He believed in intuition. He used it quite consciously in various situations of life. Anna Ivanovna, Mendeleev's wife wrote: If he
he had to solve some difficult, important vital question, he quickly, quickly, with his light gait, entered, said what was the matter, and asked me to tell my opinion on the first impression. “Just don’t think, just don’t think,” he repeated. I spoke and that was the solution."
However, nothing worked. The scribbled sheet again turned into a rebus. And time passed, in the evening it was necessary to go to the station. The main thing he already felt, felt. But this feeling had to be given a clear logical form. One can imagine how, in desperation or fury, he rushed around the office, looking around at everything that was in it, looking for a way to quickly fold the system. Finally, he grabbed a stack of cards, opened on the right page - where there was a list of simple bodies - his "Basics" and began to make an unprecedented deck of cards. Having made a deck of chemical cards, he began to play an unprecedented solitaire game. Solitaire was obviously asked! The first six lines lined up without any scandals. But then everything began to unravel.
Again and again Dmitri Ivanovich clutched at his pen and, in his impetuous handwriting, sketched columns of numbers on the sheet. And again, in bewilderment, he gave up this occupation and began to twist a cigarette and puff it so that his head was completely cloudy. At last his eyes began to droop, he flung himself on the sofa and fell sound asleep. This was not new to him. This time he didn't sleep for long—maybe a few hours, maybe a few minutes. There is no exact information about this. He woke up from the fact that he saw his solitaire in a dream, and not in the form in which he left it on the desk, but in another, more harmonious and logical. And then he jumped to his feet and began to draw up a new table on a piece of paper.
Its first difference from the previous version was that the elements were now lined up not in decreasing order, but in ascending order of atomic weights. The second is that the empty spaces inside the table were filled with question marks and atomic weights.
Rice. 8. Draft sketch compiled by D. I. Mendeleev during the discovery of the periodic law (in the course of unfolding the “chemical solitaire”). February 17 (March 1), 1869.
For a long time, Dmitry Ivanovich's story that he saw his table in a dream was treated as an anecdote. Finding anything rational in dreams was considered superstition. Nowadays, science no longer puts a blind barrier between the processes occurring in the consciousness and the subconscious. And he does not see anything supernatural in the fact that a picture that did not take shape in the process of conscious deliberation was issued in finished form as a result of an unconscious process.
Mendeleev, convinced of the existence of an objective law to which all elements of diverse properties obey, went a fundamentally different path.
Being a spontaneous materialist, he was looking for something material as a characteristic of the elements, reflecting the whole variety of their properties, taking the atomic weight of the elements as such a characteristic, Mendeleev compared the groups known at that time by the atomic weight of their members.
By writing the halogen group (F = 19, Cl = 35.5, Br = 80, J = 127) under the alkali metal group (Li = 7, Na = 23, K = 39, Rb = 85, Cs = 133) and placing under them other groups of similar elements (in ascending order of their atomic weights), Mendeleev established that the members of these natural groups form a common regular series of elements; at the same time, the chemical properties of the elements that make up such a series are periodically repeated. By placing all the 63 elements known at that time in the total "periodic system" Mendeleev discovered that the previously established natural groups organically entered this system, having lost their former artificial disunity. Later, Mendeleev formulated the periodic law discovered by him as follows: The properties of simple bodies, as well as the forms and properties of the compounds of elements, are in a periodic dependence on the values of the atomic weights of the elements.
The first version of the table of chemical elements, which expressed the periodic law, was published by Mendeleev in the form of a separate sheet called "The experience of a system of elements based on their atomic weight and chemical similarity" and sent out this leaflet in March 1869. many Russian and foreign chemists.
Rice. 9. "The experience of a system of elements based on their weight and chemical similarity."
The first table is still very imperfect, it is far from the modern form of the periodic system. But this table turned out to be the first graphic illustration of the regularity discovered by Mendeleev: “Elements arranged according to the values of their atomic weight represent a clear periodicity of properties” (“Relationship of properties with the atomic weight of elements” by Mendeleev). This article was the result of the scientist's reflections in the course of work on the "Experience of the system ...". The report on the relationship discovered by Mendeleev between the properties of elements and their atomic weights was made on March 6 (18), 1869 at a meeting of the Russian Chemical Society. Mendeleev was not present at this meeting. Instead of the absent author, the report was read by the chemist N. A. Menshutkin. In the minutes of the Russian Chemical Society, a dry note about the meeting on March 6 appeared: “N. Menshutkin reports on behalf of D. Mendeleev "the experience of a system of elements based on their atomic weight and chemical similarity." In the absence of D. Mendeleev, the discussion of this issue has been postponed until the next meeting.” N. Menshutkin's speech was published in the "Journal of the Russian Chemical Society" ("Relationship of properties with the atomic weight of elements"). In the summer of 1871, Mendeleev summed up his numerous studies related to the establishment of the periodic law in his work "Periodic Legality for the Chemical Elements" . In the classic work "Fundamentals of Chemistry", which went through 8 editions in Russian and several editions in foreign languages during Mendeleev's lifetime, Mendeleev for the first time expounded inorganic chemistry on the basis of the periodic law.
When constructing the periodic system of elements, Mendeleev overcame great difficulties, since many elements had not yet been discovered, and out of the 63 elements known by that time, nine had incorrectly determined atomic weights. Creating the table, Mendeleev corrected the atomic weight of beryllium by placing beryllium not in the same group with aluminum, as chemists usually did, but in the same group with magnesium. In 1870-71, Mendeleev changed the values of the atomic weights of indium, uranium, thorium, cerium and other elements, guided by their properties and the specified place in the periodic system. Based on the periodic law, he placed tellurium in front of iodine and cobalt in front of nickel, so that tellurium would fall in the same column with elements whose valency is 2, and iodine would fall in the same column with elements whose valency is 1, although the atomic weights of these elements required the opposite. location.
Mendeleev saw three circumstances that, in his opinion, contributed to the discovery of the periodic law:
First, the atomic weights of most chemical elements were more or less accurately determined;
Secondly, a clear concept appeared about groups of elements similar in chemical properties (natural groups);
Thirdly, by 1869 the chemistry of many rare elements had been studied, without knowledge of which it would have been difficult to come to any generalization.
Finally, the decisive step towards the discovery of the law was that Mendeleev compared all the elements with each other according to the magnitude of the atomic weights. Mendeleev's predecessors compared elements that were similar to each other. That is, elements of natural groups. These groups turned out to be unrelated. Mendeleev logically combined them in the structure of his table.
However, even after the huge and careful work of chemists to correct atomic weights, in four places of the Periodic Table the elements "violate" the strict order of arrangement in ascending atomic weights. These are pairs of elements:
18 Ar(39.948) – 19 K (39.098); 27 Co(58.933) – 28 Ni(58.69);
52 Te(127.60) – 53 I(126.904) 90 Th(232.038) – 91 Pa(231.0359).
At the time of D. I. Mendeleev, such deviations were considered shortcomings of the Periodic system. The theory of the structure of the atom put everything in its place: the elements are arranged quite correctly - in accordance with the charges of their nuclei. How, then, to explain that the atomic weight of argon is greater than the atomic weight of potassium?
The atomic weight of any element is equal to the average atomic weight of all its isotopes, taking into account their abundance in nature. By chance, the atomic weight of argon is determined by the most "heavy" isotope (it occurs in nature in greater quantities). Potassium, on the contrary, is dominated by its "lighter" isotope (that is, an isotope with a lower mass number).
Mendeleev described the course of the creative process, which is the discovery of the periodic law, as follows: “... the idea involuntarily arose that there must be a connection between mass and chemical properties. And since the mass of matter, although not absolute, but only relative, it is necessary to look for a functional correspondence between the individual properties of the elements and their atomic weights. To look for something, even mushrooms or some kind of addiction, is impossible otherwise than by looking and trying. So I began to select, writing on separate cards elements with their atomic weights and fundamental properties, similar elements and close atomic weights, which quickly led to the conclusion that the properties of elements are in a periodic dependence on their atomic weight, moreover, doubting many ambiguities, I did not doubt for a minute the generality of the conclusion drawn, since it was impossible to admit an accident.
The fundamental importance and novelty of the Periodic Law was as follows:
1. A connection was established between elements NOT SIMILAR in their properties. This relationship lies in the fact that the properties of the elements change smoothly and approximately equally with an increase in their atomic weight, and then these changes are PERIODICALLY REPEATED.
2. In those cases where it seemed that some link was missing in the sequence of changes in the properties of elements, the Periodic Table provided for GAPS that had to be filled with yet undiscovered elements.
Rice. 10. The first five periods of the Periodic table of D. I. Mendeleev. Inert gases have not yet been discovered, so they are not shown in the table. Another 4 elements unknown by the time the table was created are marked with question marks. The properties of three of them were predicted by D. I. Mendeleev with high accuracy (part of the Periodic Table of the times of D. I. Mendeleev in a more familiar form for us).
The principle used by D. I. Mendeleev to predict the properties of yet unknown elements is shown in Figure 11.
Based on the law of periodicity and practically applying the law of dialectics on the transition of quantitative changes into qualitative ones, Mendeleev already in 1869 pointed out the existence of four elements that had not yet been discovered. For the first time in the history of chemistry, the existence of new elements was predicted and even their atomic weights were roughly determined. At the end of 1870. Mendeleev, based on his system, described the properties of the still undiscovered element of group III, calling it "ekaaluminum". The scientist also suggested that the new element would be discovered using spectral analysis. Indeed, in 1875, the French chemist P.E. Lecoq de Boisbaudran, studying zinc blende with a spectroscope, discovered Mendeleev ekaaluminum in it. The exact coincidence of the supposed properties of the element with the experimentally determined ones was the first triumph and a brilliant confirmation of the predictive power of the periodic law. Descriptions of the properties of "ecaaluminum" predicted by Mendeleev and the properties of gallium discovered by Boisbaudran are given in Table 1.
| Predicted by D.I. Mendeleev |
Installed by Lecoq de Boisbaudran (1875) |
| Ekaaluminum Ea Atomic weight about 68 Simple body, must be low fusible Density close to 5.9 Atomic volume 11.5 Must not oxidize in air Must decompose water in red-hot heat Compound formulas: ЕаСl3, Еа2О3, Еа2(SO4)3 Must form Ea2(SO4)3 * M2SO4 * 24H2O alum, but more difficult than aluminum Oxide Ea2O3 should be easily reduced and give a metal more volatile than aluminum, and therefore it can be expected that EaCl3 will be discovered by spectral analysis - volatile. |
Atomic weight about 69.72 The melting point of pure gallium is 30 degrees C. The density of solid gallium is 5.904, and that of liquid gallium is 6.095 Atomic volume 11.7 Slightly oxidized only at red-hot temperatures Decomposes water at high temperature Compound formulas: GaCl3, Ga2O3, Ga2(SO4)3 Forms alum NH4Ga(SO4)2 * 12H2O Gallium is reduced from oxide by calcination in a stream of hydrogen; discovered using spectral analysis Boiling point GaCl3 215-220 degrees C |
In 1879 the Swedish chemist L. Nilson found the element scandium, which fully corresponds to the ekabor described by Mendeleev; in 1886, the German chemist K. Winkler discovered the element germanium, which corresponds to exasilicon; in 1898 French chemists Pierre Curie and Maria Sklodowska Curie discovered polonium and radium. Mendeleev considered Winkler, Lecoq de Boisbaudran and Nilsson "strengtheners of the periodic law".
The predictions made by Mendeleev were also justified: trimarganese was discovered - the current rhenium, dicesium - francium, etc.
After that, it became clear to scientists around the world that the Periodic Table of D. I. Mendeleev not only systematizes the elements, but is a graphic expression of the fundamental law of nature - the Periodic Law.
This law has predictive power. He allowed to conduct a targeted search for new, not yet discovered elements. The atomic weights of many elements, previously determined insufficiently accurately, were subjected to verification and refinement precisely because their erroneous values conflicted with the Periodic Law.
At one time, D. I. Mendeleev remarked with chagrin: "... we do not know the reasons for the periodicity." He did not manage to live to solve this mystery.
One of the important arguments in favor of the complex structure of atoms was the discovery of the periodic law of D. I. Mendeleev:
The properties of simple substances, as well as the properties and forms of compounds, are in a periodic dependence on the atomic masses of chemical elements.
When it was proved that the ordinal number of an element in the system is numerically equal to the charge of the nucleus of its atom, the physical essence of the periodic law became clear.
But why do the properties of chemical elements change periodically as the charge of the nucleus increases? Why is the system of elements constructed in this way and not otherwise, and why do its periods contain a strictly defined number of elements? There were no answers to these crucial questions.
Logical reasoning predicted that if there is a relationship between the chemical elements consisting of atoms, then the atoms have something in common and, therefore, they must have a complex structure.
The secret of the periodic system of elements was completely unraveled when it was possible to understand the most complex structure of the atom, the structure of its outer electron shells, the laws of motion of electrons around a positively charged nucleus, in which almost the entire mass of the atom is concentrated.
All chemical and physical properties of matter are determined by the structure of atoms. The periodic law discovered by Mendeleev is a universal law of nature, because it is based on the law of the structure of the atom.
The founder of the modern theory of the atom is the English physicist Rutherford, who convincing experiments showed that almost all the mass and positively charged matter of the atom is concentrated in a small part of its volume. He called this part of the atom core. The positive charge of the nucleus is compensated by the electrons revolving around it. In this model of the atom electrons resemble the planets of the solar system, as a result of which it was called planetary. Later, Rutherford managed to use experimental data to calculate the charges of nuclei. They turned out to be equal to the serial numbers of the elements in the table of D. I. Mendeleev. After the work of Rutherford and his students, Mendeleev's periodic law received a clearer meaning and a slightly different formulation:
The properties of simple substances, as well as the properties and forms of the combination of elements, are in a periodic dependence on the charge of the nucleus of the atoms of the elements.
Thus, the serial number of a chemical element in the periodic system received a physical meaning.
In 1913, G. Moseley studied the X-ray emission of a number of chemical elements in Rutherford's laboratory. For this purpose, he designed the anode of an X-ray tube from materials consisting of certain elements. It turned out that the wavelengths of the characteristic X-ray radiation increase with an increase in the serial number of the elements that make up the cathode. G. Moseley derived an equation relating the wavelength and the serial number Z:
This mathematical expression is now called Moseley's law. It makes it possible to determine the serial number of the element under study from the measured X-ray wavelength.
The simplest atomic nucleus is the nucleus of the hydrogen atom. Its charge is equal and opposite in sign to the charge of an electron, and its mass is the smallest of all nuclei. The nucleus of the hydrogen atom was recognized as an elementary particle, and in 1920 Rutherford gave it the name proton . The mass of a proton is approximately one atomic mass unit.
However, the mass of all atoms, except for hydrogen, numerically exceeds the charges of the nuclei of atoms. Already Rutherford assumed that in addition to protons, nuclei should contain some neutral particles with a certain mass. These particles were discovered in 1932 by Bothe and Becker. Chadwick established their nature and named neutrons . A neutron is an uncharged particle with a mass almost equal to that of a proton, i.e. also 1 AU. eat.
In 1932, the Soviet scientist D. D. Ivanenko and the German physicist Heisenberg independently developed the proton-neutron theory of the nucleus, according to which the nuclei of atoms consist of protons and neutrons.
Consider the structure of an atom of some element, for example, sodium, from the standpoint of the proton-neutron theory. The serial number of sodium in the periodic system is 11, the mass number is 23. In accordance with the serial number, the charge of the nucleus of the sodium atom is + 11. Therefore, there are 11 electrons in the sodium atom, the sum of the charges of which is equal to the positive charge of the nucleus. If the sodium atom loses one electron, then the positive charge will be one more than the sum of the negative charges of the electrons (10), and the sodium atom will become an ion with a charge of 1+. The charge of the nucleus of an atom is equal to the sum of the charges of 11 protons in the nucleus, the mass of which is 11 AU. e. m. Since the mass number of sodium is 23 a.m. e.m., then the difference 23 - 11 \u003d 12 determines the number of neutrons in the sodium atom.
Protons and neutrons are called nucleons . The nucleus of the sodium atom consists of 23 nucleons, of which 11 are protons and 12 are neutrons. The total number of nucleons in the nucleus is written at the top left of the element designation, and the number of protons at the bottom left, eg Na.
All atoms of a given element have the same nuclear charge, i.e., the same number of protons in the nucleus. The number of neutrons in the nuclei of atoms of elements can be different. Atoms that have the same number of protons and different numbers of neutrons in their nuclei are called isotopes .
Atoms of different elements whose nucleus contains the same number of nucleons are called isobars .
Science owes the establishment of a real connection between the structure of the atom and the structure of the periodic system, first of all, to the great Danish physicist Niels Bohr. He was also the first to explain the true principles of the periodic change in the properties of elements. Bohr began by making Rutherford's model of the atom viable.
Rutherford's planetary model of the atom reflected the obvious truth that the main part of the atom is contained in a negligible part of the volume - the atomic nucleus, and electrons are distributed in the rest of the volume of the atom. However, the nature of the motion of an electron in orbit around the nucleus of an atom contradicts the theory of motion of electric charges of electrodynamics.
First, according to the laws of electrodynamics, an electron rotating around a nucleus must fall onto the nucleus as a result of energy loss for radiation. Secondly, when approaching the nucleus, the wavelengths emitted by the electron must continuously change, forming a continuous spectrum. However, atoms do not disappear, which means that electrons do not fall on the nucleus, and the radiation spectrum of atoms is not continuous.
If the metal is heated to the evaporation temperature, then its vapor will begin to glow, and the vapor of each metal has its own color. The radiation of a metal vapor decomposed by a prism forms a spectrum consisting of individual luminous lines. Such a spectrum is called a line spectrum. Each line of the spectrum is characterized by a certain frequency of electromagnetic radiation.
In 1905, Einstein, explaining the phenomenon of the photoelectric effect, suggested that light propagates in the form of photons or energy quanta, which have a very definite meaning for each type of atom.
In 1913, Bohr introduced a quantum representation into Rutherford's planetary model of the atom and explained the origin of the line spectra of atoms. His theory of the structure of the hydrogen atom is based on two postulates.
First postulate:
The electron revolves around the nucleus, without radiating energy, along strictly defined stationary orbits that satisfy the quantum theory.
In each of these orbits, the electron has a certain energy. The farther from the nucleus the orbit is located, the more energy the electron located on it has.
The movement of an object around a center in classical mechanics is determined by the angular momentum m´v´r, where m is the mass of the moving object, v is the speed of the object, r is the radius of the circle. According to quantum mechanics, the energy of this object can only have certain values. Bohr believed that the angular momentum of an electron in a hydrogen atom can only be equal to an integer number of action quanta. Apparently, this ratio was Bohr's conjecture, later it was derived mathematically by the French physicist de Broglie.
Thus, the mathematical expression of Bohr's first postulate is the equality:
(1)
In accordance with equation (1), the minimum radius of the electron orbit, and, consequently, the minimum potential energy of the electron corresponds to the value of n equal to unity. The state of the hydrogen atom, which corresponds to the value n=1, is called normal or basic. A hydrogen atom whose electron is in any other orbit corresponding to the values n=2, 3, 4, ¼ is called excited.
Equation (1) contains the electron velocity and the radius of the orbit as unknowns. If we make another equation, which will include v and r, then we can calculate the values of these important characteristics of the electron in the hydrogen atom. Such an equation is obtained by taking into account the equality of the centrifugal and centripetal forces acting in the "nucleus of a hydrogen atom - electron" system.
The centrifugal force is . The centripetal force, which determines the attraction of an electron to the nucleus, according to Coulomb's law is . Taking into account the equality of the charges of the electron and the nucleus in the hydrogen atom, we can write:
(2)
Solving the system of equations (1) and (2) with respect to v and r, we find:
(3)
Equations (3) and (4) make it possible to calculate the orbital radii and electron velocities for any value of n. At n=1, the radius of the first orbit of the hydrogen atom, the Bohr radius, is equal to 0.053 nm. The speed of the electron in this orbit is 2200 km/s. equations (3) and (4) show that the radii of the electron orbits of the hydrogen atom are related to each other as the squares of natural numbers, and the speed of the electron decreases with increasing n.
Second postulate:
When moving from one orbit to another, an electron absorbs or emits a quantum of energy.
When an atom is excited, i.e., when an electron moves from an orbit closest to the nucleus to a more distant one, an energy quantum is absorbed and, conversely, when an electron moves from a distant orbit to a nearby one, quantum energy E 2 - E 1 \u003d hv is emitted. After finding the radii of the orbits and the energy of the electron on them, Bohr calculated the energy of photons and their corresponding lines in the line spectrum of hydrogen, which corresponded to the experimental data.
The number n, which determines the size of the radii of quantum orbits, the speed of movement of electrons and their energy, is called principal quantum number .
Sommerfeld further improved Bohr's theory. He proposed that in an atom there can be not only circular, but also elliptical orbits of electrons, and on the basis of this he explained the origin of the fine structure of the hydrogen spectrum.
Rice. 12. An electron in a Bohr atom describes not only circular, but also elliptical orbits. Here's what they look like for different values l at P =2, 3, 4.
However, the Bohr-Sommerfeld theory of the structure of the atom combined classical and quantum mechanical concepts and, thus, was built on contradictions. The main disadvantages of the Bohr–Sommerfeld theory are as follows:
1. The theory is not capable of explaining all the details of the spectral characteristics of atoms.
2. It does not make it possible to quantitatively calculate the chemical bond even in such a simple molecule as a hydrogen molecule.
But the fundamental position was firmly established: the filling of electron shells in the atoms of chemical elements occurs starting from the third, M - shells are not sequential, gradually to full capacity (i.e., as it was with TO- And L - shells), but stepwise. In other words, the construction of electron shells is temporarily interrupted due to the fact that electrons appear in atoms that belong to other shells.
These letters are designated as follows: n , l , m l , m s – and in the language of atomic physics are called quantum numbers. Historically, they were introduced gradually, and their emergence is largely associated with the study of atomic spectra.
So it turns out that the state of any electron in an atom can be written in a special code, which is a combination of four quantum numbers. These are not just some abstract quantities used to record electronic states. On the contrary, they all have a real physical content.
Number P is included in the formula for the capacitance of the electron shell (2 P 2), i.e. the given quantum number P corresponds to the number of the electron shell; in other words, this number determines whether an electron belongs to a given electron shell.
Number P accepts only integer values: 1, 2, 3, 4, 5, 6, 7,…, corresponding to shells respectively: K, L, M, N, O, P, Q.
Because the P is included in the formula for the energy of an electron, then they say that the main quantum number determines the total energy of an electron in an atom.
Another letter of our alphabet - the orbital (side) quantum number - is denoted as l . It was introduced to emphasize the non-equivalence of all electrons belonging to a given shell.
Each shell is subdivided into certain subshells, and their number is equal to the number of the shell. i.e. K-shell ( P =1) consists of one subshell; L-shell ( P =2) - out of two; M-shell ( P =3) - from three subshells ...
And each subshell of this shell is characterized by a certain value l . The orbital quantum number also takes integer values, but starting from zero, i.e. 0, 1, 2, 3, 4, 5, 6 ... Thus, l always less P . It is easy to understand that when P =1 l =0; at n =2 l =0 and 1; at n = 3 l = 0, 1 and 2, etc. Number l , so to speak, has a geometric image. After all, the orbits of electrons belonging to one shell or another can be not only circular, but also elliptical.
different meanings l and characterize different types of orbits.
Physicists love traditions and prefer old letter designations to designate electron subshells. s ( l =0), p ( l =1), d ( l =2), f ( l =3). These are the first letters of German words characterizing the features of the series of spectral lines due to electron transitions: sharp, main, diffuse, fundamental.
Now you can briefly write down which electron subshells are contained in the electron shells (Table 2).
To know how many electrons the various electron subshells contain, help determine the third and fourth quantum numbers - m l and m s, which are called magnetic and spin.
Magnetic quantum number m l closely related to l and determines, on the one hand, the direction of location of these orbits in space, and on the other hand, their number possible for a given l . From some laws of atomic theory it follows that for a given l quantum number m l, takes 2 l +1 integer values: from - l to + l , including zero. For example, for l =3 this is the sequence m l we have: - 3, - 2, - 1, 0, +1, +2, +3, i.e. seven values in total.
Why m l called magnetic? Each electron, revolving in orbit around the nucleus, is essentially one turn of the winding, through which an electric current flows. There is a magnetic field, so each orbit in the atom can be considered as a flat magnetic sheet. When an external magnetic field is found, each electron orbit will interact with this field and tend to occupy a certain position in the atom.
The number of electrons in each orbit is determined by the value of the spin quantum number m s .
The behavior of atoms in strong non-uniform magnetic fields has shown that each electron in an atom behaves like a magnet. And this indicates that the electron rotates around its own axis, like a planet in orbit. This property of the electron is called "spin" (translated from English - to rotate). The rotational motion of an electron is constant and unchanging. The rotation of an electron is completely unusual: it cannot be slowed down, accelerated, or stopped. It is the same for all electrons in the world.
But although spin is a common property of all electrons, it is also the reason for the difference between electrons in an atom.
Two electrons, revolving in the same orbit around the nucleus, have the same spin in magnitude, and yet they can differ in the direction of their own rotation. In this case, the sign of the angular momentum and the sign of the spin change.
Quantum calculation leads to two possible values of the spin quantum numbers inherent in an electron in orbit: s=+ and s= - . There can be no other values. Therefore, in an atom, either only one or two electrons can rotate in each orbit. There can be no more.
Each electron subshell can accommodate 2(2 l + 1) - electrons, namely (table 3):
From here, by simple addition, the capacities of successive shells are obtained.
The simplicity of the basic law, to which the initial infinite complexity of the structure of the atom was reduced, is amazing. All the whimsical behavior of electrons in its outer shell, which governs all its properties, can be expressed with extraordinary simplicity: There are not and cannot be two identical electrons in an atom. This law is known in science as the Pauli principle (after the Swiss theoretical physicist).
Knowing the total number of electrons in an atom, which is equal to its serial number in the Mendeleev system, you can "build" an atom: you can calculate the structure of its outer electron shell - determine how many electrons are in it and what kind they are in it.
As you grow Z similar types of electronic configurations of atoms are periodically repeated. In fact, this is also a formulation of the periodic law, but in relation to the process of distribution of electrons over shells and subshells.
Knowing the law of the structure of the atom, you can now build a periodic system and explain why it is built that way. Only one small terminological clarification is needed: those elements in whose atoms the construction of s-, p-, d-, f-subshells occurs are usually called s-, p-, d-, f-elements, respectively.
It is customary to write the formula of an atom in this form: the main quantum number is the corresponding number, the secondary quantum number is the letter, the number of electrons is marked on the top right.
The first period contains 1 s-elements - hydrogen and helium. Schematic representation of the first period is as follows: 1 s 2 . The second period can be represented as follows: 2 s 2 2 p 6 , i.e., it includes elements in which 2 s-, 2 p-subshells are filled. And the third one (3 s-, 3p-subshells are built in it): 3 s 2 3p 6 . Obviously, similar types of electronic configurations are repeated.
At the beginning of the 4th period, there are two 4 s-elements, i.e., the filling of the N-shell begins earlier than the construction of the M-shell was completed. It contains 10 more vacancies, which are filled in the next ten elements (3 d-elements). The filling of the M-shell has ended, the filling of the N-shell continues (with six 4 p-electrons). Consequently, the structure of the 4th period is as follows: 4 s 2 3 d 10 4 p 6 . The fifth period is filled in the same way:
5 s 2 4 d 10 5 p 6 .
There are 32 elements in the sixth period. Its schematic representation is as follows: 6 s 2 4 f 14 5 d 10 6 p 6 .
And, finally, the next, 7th period: 7 s 2 5 f 14 6 d 10 7 p 6 . It should be borne in mind that not all elements of the 7th period are known yet.
Such stepwise filling of shells is a strict physical regularity. It turns out that instead of occupying the levels of the 3 d subshell, it is more profitable for electrons (from the energy point of view) to first populate the levels of the 4 s subshell. It is these energy "swings" "more profitable - more unprofitable" and explain the situation that in chemical elements the filling of electron shells goes in ledges.
In the mid 20s. French physicist L. de Broglie expressed a bold idea: all material particles (including electrons) have not only material, but also wave properties. Soon it was possible to show that electrons, like light waves, can also go around obstacles.
Since an electron is a wave, its motion in an atom can be described using the wave equation. Such an equation was derived in 1926 by the Austrian physicist E. Schrödinger. Mathematicians call it a second-order partial differential equation. For physicists, this is the basic equation of quantum mechanics.
Here's what that equation looks like:
+++ y=0
Where m is the electron mass; r – the distance of an electron from the nucleus; e is the electron charge; E is the total energy of the electron, which is equal to the sum of the kinetic and potential energies; Z is the serial number of the atom (for a hydrogen atom it is equal to 1); h- "quantum of action"; x , y , z – electron coordinates; y - wave function (abstract abstract quantity characterizing the degree of probability).
The degree of probability that an electron is located in a certain place in the space around the nucleus. If y \u003d 1, then, therefore, the electron must really be in this very place; if y = 0, then there is no electron there at all.
The concept of the probability of finding an electron is central to quantum mechanics. And the value of the y (psi)-function (more precisely, the square of its value) expresses the probability of an electron being at one or another point in space.
There are no definite electron orbits in the quantum mechanical atom, which are so clearly outlined in the Bohr model of the atom. The electron is as if smeared in space in the form of a cloud. But the density of this cloud is different: as they say, where it is dense, and where it is empty. A higher cloud density corresponds to a higher probability of finding an electron.
From the abstract quantum-mechanical model of the atom, one can move on to Bohr's visual and visible model of the atom. To do this, you need to solve the Schrödinger equation. It turns out that the wave function is associated with three different quantities, which can only take integer values. Moreover, the sequence of changes in these quantities is such that they cannot be anything other than quantum numbers. Main, orbital and magnetic. But they were introduced specifically to designate the spectra of various atoms. Then they very organically migrated to the Bohr model of the atom. Such is scientific logic - even the most severe skeptic will not undermine it.
All this means that the solution of the Schrödinger equation ultimately leads to the derivation of the sequence of filling the electron shells and subshells of atoms. This is the main advantage of the quantum mechanical atom over the Bohr atom. And the concepts familiar to the planetary atom can be revised from the point of view of quantum mechanics. We can say that the orbit is a certain set of probable positions of a given electron in an atom. It corresponds to a certain wave function. Instead of the term "orbit" in modern atomic physics and chemistry, the term "orbital" is used.
So, the Schrödinger equation is like a magic wand that eliminates all the shortcomings contained in the formal theory of the periodic system. Turns "formal" into "actual".
In reality, this is far from the case. Because the equation only has an exact solution for the hydrogen atom, the simplest of atoms. For the helium atom and subsequent ones, it is impossible to solve the Schrödinger equation exactly, since the forces of interaction between electrons are added. And taking into account their influence on the final result is a mathematical problem of unimaginable complexity. It is inaccessible to human abilities; only high-speed electronic computers, carrying out hundreds of thousands of operations per second, can be compared with it. And even then only on condition that the program for calculations is developed with numerous simplifications and approximations.
For 40 years, the list of known chemical elements has increased by 19. And all 19 elements were synthesized, prepared artificially.
The synthesis of elements can be understood as obtaining from an element with a lower nuclear charge, a lower atomic number of an element with a higher atomic number. And the process of obtaining is called a nuclear reaction. Its equation is written in the same way as the equation of an ordinary chemical reaction. The reactants are on the left, the products are on the right. The reactants in a nuclear reaction are the target and the bombarding particle.
Almost any element of the periodic system (in free form or in the form of a chemical compound) can serve as a target.
The role of bombarding particles is played by a-particles, neutrons, protons, deuterons (nuclei of the heavy isotope of hydrogen), as well as the so-called multiply charged heavy ions of various elements - boron, carbon, nitrogen, oxygen, neon, argon and other elements of the periodic system.
For a nuclear reaction to occur, the bombarding particle must collide with the nucleus of the target atom. If the particle has a sufficiently high energy, then it can penetrate so deeply into the nucleus that it merges with it. Since all the particles listed above, except for the neutron, carry positive charges, then, merging with the nucleus, they increase its charge. And changing the value of Z means the transformation of elements: the synthesis of an element with a new value of the nuclear charge.
In order to find a way to accelerate the bombarding particles, to give them a large energy sufficient to merge them with the nuclei, a special particle accelerator, the cyclotron, was invented and constructed. Then they built a special factory of new elements - a nuclear rector. Its direct purpose is to generate nuclear energy. But since there are always intense neutron fluxes in it, they are easy to use for the purposes of artificial synthesis. The neutron has no charge, and therefore it is not necessary (and impossible) to accelerate. On the contrary, slow neutrons turn out to be more useful than fast ones.
Chemists had to rack their brains and show genuine miracles of ingenuity in order to develop ways to separate negligible amounts of new elements from the target substance. To learn to study the properties of new elements when only a few of their atoms were available...
By the work of hundreds and thousands of scientists, 19 new cells were filled in the periodic system. Four are within its old boundaries: between hydrogen and uranium. Fifteen - for uranium. Here's how it all happened...
4 places in the periodic system remained empty for a long time: cells with No. 43, 61, 85 and 87.
These 4 elements were elusive. The efforts of scientists aimed at searching for them in nature remained unsuccessful. With the help of the periodic law, all other places in the periodic table were filled long ago - from hydrogen to uranium.
More than once in scientific journals there were reports of the discovery of these four elements. But all these discoveries were not confirmed: each time an exact check showed that a mistake had been made and random insignificant impurities were mistaken for a new element.
A long and difficult search finally led to the discovery in nature of one of the elusive elements. It turned out that ecacesium No. 87 occurs in the chain of decay of the natural radioactive isotope uranium-235. it is a short-lived radioactive element.
Rice. 13. Scheme of the formation of element No. 87 - France. Some radioactive isotopes can decay in two ways, for example, through both a- and b-decay. This phenomenon is called a radioactive fork. All natural radioactive families contain forks.
Element 87 deserves to be told in more detail. Now in chemistry encyclopedias we read: francium (serial number 87) was discovered in 1939 by the French scientist Marguerite Perey.
How did Perey manage to capture the elusive element? In 1914, three Austrian radiochemists - S. Meyer, W. Hess and F. Panet - began to study the radioactive decay of the actinium isotope with a mass number of 227. It was known that it belongs to the actinouranium family and emits b-particles; hence its decay product is thorium. However, scientists had vague suspicions that actinium-227, in rare cases, also emits a-particles. In other words, one of the examples of a radioactive fork is observed here. In the course of such a transformation, an isotope of element 87 should be formed. Meyer and his colleagues actually observed a-particles. Further studies were required, but they were interrupted by the First World War.
Marguerite Perey followed the same path. But she had at her disposal more sensitive instruments, new, improved methods of analysis. so she was successful.
Francium is one of the artificially synthesized elements. But still, the element was first discovered in nature. It is an isotope of francium-223. Its half-life is only 22 minutes. It becomes clear why there is so little France on Earth. Firstly, because of its fragility, it does not have time to concentrate in any noticeable quantities, and secondly, the process of its formation itself is characterized by a low probability: only 1.2% of actinium-227 nuclei decays with the emission of a-particles.
In this regard, francium is more profitable to prepare artificially. Already received 20 isotopes of francium, and the longest-lived of them - francium-223. working with very small amounts of francium salts, chemists were able to prove that its properties are extremely similar to cesium.
Studying the properties of atomic nuclei, physicists came to the conclusion that elements with atomic numbers 43, 61, 85 and 87 cannot have stable isotopes. They can only be radioactive, with short half-lives, and should disappear quickly. Therefore, all these elements were created by man artificially. The paths for creating new elements were indicated by the periodic law. Element 43 was the first artificially created.
There must be 43 positive charges in the nucleus of element 43, and 43 electrons must revolve around the nucleus. The empty space for element 43, which is in the middle of the fifth period, has manganese in the fourth period, and rhenium in the sixth. Therefore, the chemical properties of element 43 should be similar to those of manganese and rhenium. To the left of cell 43 is molybdenum #42, to the right is ruthenium #44. Therefore, to create element 43, it is necessary to increase the number of charges in the nucleus of an atom, which has 42 charges, by one more elementary charge. Therefore, for the synthesis of a new element 43, molybdenum must be taken as a feedstock. The lightest element, hydrogen, has one positive charge. So, we can expect that element 43 can be obtained as a result of a nuclear reaction between molybdenum and a proton.
Rice. 14. Scheme for the synthesis of element No. 43 - technetium.
The properties of element 43 should be similar to those of manganese and rhenium, and in order to detect and prove the formation of this element, one must use chemical reactions similar to those by which chemists determine the presence of small amounts of manganese and rhenium.
This is how the periodic system makes it possible to chart the way for the creation of artificial elements.
In exactly the same way, the first artificial chemical element was created in 1937. He received the significant name of technetium - the first element made by technical, artificial means. This is how technetium was synthesized. The plate of molybdenum was subjected to intense bombardment by nuclei of the heavy isotope of hydrogen - deuterium, which were dispersed in the cyclotron to great speed.
Heavy hydrogen nuclei, which received very high energy, penetrated the molybdenum nuclei. After irradiation in the cyclotron, the molybdenum plastic was dissolved in acid. An insignificant amount of a new radioactive substance was isolated from the solution using the same reactions that are necessary for the analytical determination of manganese (analogous to element 43). This was a new element - technetium. They correspond exactly to the position of the element in the periodic table.
Now technetium has become quite affordable: it is formed in fairly large quantities in nuclear reactors. Technetium has been well studied and is already being used in practice.
The method by which element 61 was created is very similar to the method by which technetium is obtained. Element 61 was isolated only in 1945 from fragmentation elements formed in a nuclear reactor as a result of the fission of uranium.
Rice. 15. Scheme for the synthesis of element No. 61 - promethium.
The element received the symbolic name "promethium". This name was not given to him with a simple reason. It symbolizes the dramatic path of science stealing the energy of nuclear fission from nature and mastering this energy (according to legend, the titan Prometheus stole fire from the sky and gave it to people; for this he was chained to a rock and a huge eagle tormented him every day), but it also warns people from a terrible military danger.
Promethium is now produced in considerable quantities: it is used in atomic batteries - direct current sources that can operate without interruption for many years.
The heaviest halogen, ecaiod, element 85 was synthesized in a similar way. It was first obtained by bombarding bismuth (No. 83) with helium nuclei (No. 2), accelerated in a cyclotron to high energies. The new element is named astatine (unstable). It is radioactive and disappears quickly. Its chemical properties also turned out to correspond exactly to the periodic law. It is similar to iodine.
Rice. 16. Scheme for the synthesis of element No. 85 - astatine.
Transuranium elements are artificially synthesized chemical elements that are located in the periodic system after uranium. How many more of them will be synthesized in the future, while no one can definitely answer.
Uranium was the last in the natural series of chemical elements for a long 70 years.
And all this time, scientists, of course, were worried about the question: do elements heavier than uranium exist in nature? Dmitry Ivanovich believed that if transuranium elements could ever be found in the bowels of the earth, then their number should be limited. After the discovery of radioactivity, the absence of such elements in nature was explained by the fact that their half-lives are short and they all decayed, turned into lighter elements, a very long time ago, at the earliest stages of the evolution of our planet. But uranium, which turned out to be radioactive, had such a long lifespan that it survived to our time. Why, at least for the nearest transuranics, nature could not release such a generous time for existence? There were many reports of the discovery of supposedly new elements within the system - between hydrogen and uranium, but almost never in scientific journals did they write about the discovery of transurans. Scientists only argued what was the reason for the break in the periodic system on uranium.
Only nuclear fusion made it possible to establish interesting circumstances that could not even be suspected before.
The first studies on the synthesis of new chemical elements were aimed at the artificial production of transurans. The first artificial transuranium element was talked about three years before technetium appeared. The stimulating event was the discovery of the neutron. an elementary particle, devoid of charge, had an enormous penetrating power, could reach the atomic nucleus without encountering any obstacles, and cause transformations of various elements. Neutrons began to fire at targets from a variety of substances. The outstanding Italian physicist E. Fermi became the pioneer of research in this area.
Uranium irradiated with neutrons showed unknown activity with a short half-life. Uranium-238, having absorbed a neutron, turns into an unknown isotope of the element uranium-239, which is b-radioactive and should turn into an isotope of an element with serial number 93. A similar conclusion was made by E. Fermi and his colleagues.
In fact, it took a lot of effort to prove that the unknown activity really corresponds to the first transuranium element. Chemical operations led to the conclusion: the new element is similar in its properties to manganese, that is, it belongs to the VII b-subgroup. This argument turned out to be impressive: at that time (in the 30s), almost all chemists believed that if transuranium elements existed, then at least the first of them would be similar d-elements from previous periods. It was a mistake that undoubtedly affected the course of the history of the discovery of elements heavier than uranium.
In a word, in 1934, E. Fermi confidently announced the synthesis of not only element 93, to which he gave the name "ausonium", but also its right neighbor in the periodic table - "hesperium" (No. 94). The latter was a b-decay product of ausonium:
There were scientists who "pulled" this chain even further. Among them: German researchers O. Hahn, L. Meitner and F. Strassmann. In 1937, they already spoke, as if about something real, of element No. 97:
But none of the new elements was obtained in any noticeable quantities, was not isolated in a free form. Their synthesis was judged by various indirect signs.
Ultimately, it turned out that all these ephemeral substances, taken for transuranium elements, are in fact elements belonging ... to the middle of the periodic system, that is, artificial radioactive isotopes of long-known chemical elements. This became clear when O. Hahn and F. Strassmann made on December 22, 1938 one of the greatest discoveries of the 20th century. - the discovery of uranium fission under the action of slow neutrons. Scientists have irrefutably established that uranium irradiated with neutrons contains isotopes of barium and lanthanum. They could be formed only under the assumption that neutrons, as it were, disintegrate uranium nuclei into several smaller fragments.
The division mechanism was explained by L. Meitner and O. Frisch. The so-called drop model of the nucleus already existed: the atomic nucleus was likened to a drop of liquid. If sufficient energy is given to the drop, if it is excited, then it can be divided into smaller drops. Likewise, the nucleus, brought into an excited state by a neutron, is capable of disintegrating, splitting into smaller parts - the nuclei of atoms of lighter elements.
In 1940, Soviet scientists G. N. Flerov and K. A. Petrzhak proved that the fission of uranium can occur spontaneously. Thus, a new type of radioactive transformations occurring in nature, the spontaneous fission of uranium, was discovered. This was an extremely important discovery.
However, it is wrong to declare research on transuraniums in the 1930s as erroneous.
Uranium has two main natural isotopes: uranium-238 (significantly predominant) and uranium-235. The second is mainly fissioned under the action of slow neutrons, while the first, absorbing a neutron, only turns into a heavier isotope - uranium-239, and this absorption is the more intense, the faster the bombarding neutrons. Therefore, in the first attempts to synthesize transuraniums, the effect of slowing down neutrons led to the fact that when “shelling” a target made of natural uranium containing and , the fission process prevailed.
But the uranium-238 that absorbed the neutron was bound to give rise to the chain of formation of transuranium elements. It was necessary to find a reliable way to trap the atoms of element 93 in the most complex mess of fission fragments. Comparatively smaller in mass, these fragments in the process of bombarding uranium should have flown away over long distances (have a longer path) than the very massive atoms of element 93.
These considerations were based on the American physicist E. Macmillan, who worked at the University of California, as the basis for his experiments. In the spring of 1939, he began to carefully study the distribution of uranium fission fragments along the length of the runs. He managed to separate a small portion of fragments with an insignificant path length. It was in this portion that he found traces of a radioactive substance with a half-life of 2.3 days and a high radiation intensity. Such activity was not observed in other fragment fractions. Macmillan was able to show that this substance X is a decay product of the uranium-239 isotope:
The chemist F. Ableson joined the work. It turned out that a radioactive substance with a half-life of 2.3 days can be chemically separated from uranium and thorium and has nothing to do with rhenium. Thus collapsed the assumption that element 93 must be an excarnation.
The successful synthesis of neptunium (the new element was named after a planet in the solar system) was announced by the American journal Physical Review at the beginning of 1940. Thus began the era of the synthesis of transuranium elements, which turned out to be very important for the further development of Mendeleev's theory of periodicity.
Rice. 17. Scheme for the synthesis of element No. 93 - neptunium.
Even the periods of the longest-lived isotopes of transuranium elements, as a rule, are significantly inferior to the age of the Earth, and therefore their existence in nature is now practically excluded. Thus, the reason for the break in the natural series of chemical elements on uranium, element 92, is clear.
Neptunium was followed by plutonium. It was synthesized by a nuclear reaction:
winter 1940-1941 by the American scientist G. Seaborg and co-workers (several more new transuranium elements were subsequently synthesized in the laboratory of G. Seaborg). But the most important isotope of plutonium turned out to be with a half-life of 24,360 years. In addition, plutonium-239 under the action of slow neutrons fissions much more intensively than
Rice. 18. Scheme for the synthesis of element No. 94 - plutonium.
In the 40s. three more elements heavier than uranium were synthesized: americium (in honor of America), curium (in honor of M. and P. Curie) and berkelium (in honor of Berkeley in California). The target in nuclear reactors was plutonium-239, bombarded by neutrons and a-particles, and americium (its irradiation led to the synthesis of berkelium):
.
50s started with the synthesis of californium (No. 98). It was obtained when the long-lived curium-242 isotope was accumulated in significant quantities and a target was made from it. Nuclear reaction: 
led to the synthesis of the new element 98.
In order to move towards elements 99 and 100, care had to be taken to accumulate weight amounts of berkelium and californium. The bombardment of targets made from them with a-particles provided grounds for synthesizing new elements. But the half-lives (hours and minutes) of the synthesized isotopes of elements 97 and 98 were too short, and this turned out to be an obstacle to their accumulation in the required quantities. Another way was also proposed: long-term irradiation of plutonium with an intense neutron flux. But one would have to wait for the results for many years (in order to obtain one of the isotopes of berkelium in its pure form, the plutonium target was irradiated for as long as 6 years!). There was only one way to significantly reduce the synthesis time: to sharply increase the power of the neutron beam. In laboratories, this was not possible.
A thermonuclear explosion came to the rescue. On November 1, 1952, the Americans detonated a thermonuclear device on the Eniwetok Atoll in the Pacific Ocean. At the site of the explosion, several hundred kilograms of soil were collected, samples were examined. As a result, it was possible to detect isotopes of elements 99 and 100, named respectively einsteinium (in honor of A. Einstein) and fermium (in honor of E. Fermi).
The neutron flux formed during the explosion turned out to be very powerful, so that the uranium-238 nuclei were able to absorb a large number of neutrons in a very short period of time. These superheavy isotopes of uranium, as a result of chains of successive -decays, turned into isotopes of einsteinium and fermium (Figure 19).
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Rice. 19. Scheme for the synthesis of elements No. 99 - einsteinium and No. 100 - fermium.
Mendeleev named chemical element No. 101, synthesized by American physicists led by G. Seaborg in 1955. The authors of the synthesis named the new element "in recognition of the merits of the great Russian chemist, who was the first to use the periodic system to predict the properties of undiscovered chemical elements." Scientists managed to accumulate enough einsteinium to prepare a target from it (the amount of einsteinium was measured in a billion atoms); irradiating it with a-particles, it was possible to calculate for the synthesis of the nuclei of element 101 (Figure 20):
Rice. 20. Scheme for the synthesis of element No. 101 - mendeleevium.
The half-life of the resulting isotope turned out to be much longer than theorists thought. And although a few atoms of mendeleevium were obtained as a result of synthesis, it turned out to be possible to study their chemical properties by the same methods that were used for previous transurans.
A worthy assessment of the periodic law was given by William Razmay, who argued that the periodic law is a true compass for researchers.
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It is impossible to study chemistry except on the basis of this omnipresent law. How ridiculous would a chemistry textbook look without the periodic table! You need to understand how the different elements are related and why they are so connected. Only then will the periodic system turn out to be the richest repository of information about the properties of elements and their compounds, such a repository with which little can be compared.
An experienced chemist, just by looking at the place occupied by any element in the system, can tell a lot about it: a given element is a metal or a non-metal; whether or not it forms compounds with hydrogen - hydrides; what oxides are characteristic of this element; what valencies it can show when entering into chemical compounds; which compounds of this element will be stable, and which, on the contrary, will be fragile; from which compounds and in what way it is most convenient and profitable to obtain this element in a free form. And if a chemist is able to extract all this information from the periodic system, then this means that he has mastered it well.
The periodic system is the basis for obtaining new materials and substances with new, unusual, predetermined properties, such substances that are unknown to nature. They are being created now in large numbers. It also became a guiding thread for the synthesis of semiconductor materials. Scientists have found in many examples that compounds of elements that occupy certain places in the periodic table (mainly in its III-V groups) have or should have the best semiconductor properties.
It is impossible to set the task of obtaining new alloys, ignoring the periodic system. After all, the structure and properties of alloys are determined by the position of the metals in the table. Currently, thousands of different alloys are known.
Perhaps in any branch of modern chemistry one can notice a reflection of the periodic law. But not only chemists bow their heads before his greatness. In the difficult and fascinating business of synthesizing new elements, it is impossible to do without the periodic law. A gigantic natural process of synthesis of chemical elements takes place in stars. Scientists call this process nucleosynthesis.
So far, scientists have no idea in what ways, as a result of which successive nuclear reactions, the chemical elements known to us were formed. There are many hypotheses of nucleosynthesis, but there is no complete theory yet. But it is safe to say that even the most timid assumptions about the ways of the origin of elements would be impossible without taking into account the sequential arrangement of elements in the periodic system. Regularities of nuclear periodicity, structure and properties of atomic nuclei underlie various reactions of nucleosynthesis.
It would take a long time to enumerate those areas of human knowledge and practice where the Great Law and the system of elements play an important role. And, in truth, we do not even imagine the full scale of Mendeleev's theory of periodicity. Many times it will still flash before scientists with its unexpected facets.
Mendeleev is undoubtedly one of the greatest chemists in the world. Although more than a hundred years have passed since his law, no one knows when the entire content of the famous periodic table will be fully understood.
Rice. 21. Photo by Dmitry Ivanovich Mendeleev.
Rice. 22. Russian Chemical Society chaired by
1. Petryanov I. V., Trifonov D. N. “The Great Law”
Moscow, Pedagogy, 1984
2. Kedrov B. M. “Forecasts of D. I. Mendeleev in atomistics”
Moscow, Atomizdat, 1977
3. Agafoshin N. P. "Periodic law and the periodic system of elements of D. I. Mendeleev" Moscow, "Enlightenment", 1973
4. "D. I. Mendeleev in the memoirs of contemporaries "Moscow," Atomizdat ", 1973
5. Volkov V. A. Biographical reference book "Outstanding chemists of the world" Moscow, "Higher School", 1991
6. Bogolyubova L. N. "Biographies of great chemists" Moscow, "Enlightenment", 1997
7. Ivanova L. F., Egorova E. N. desktop encyclopedia "Everything about everything" Moscow, "Mnemozina", 2001
8. Summ L. B. children's encyclopedia “I know the world. Chemistry" Moscow, "Olimp", 1998
The discovery of the table of periodic chemical elements was one of the important milestones in the history of the development of chemistry as a science. The pioneer of the table was the Russian scientist Dmitry Mendeleev. An extraordinary scientist with the broadest scientific horizons managed to combine all ideas about the nature of chemical elements into a single coherent concept.
About the history of the discovery of the table of periodic elements, interesting facts related to the discovery of new elements and folk tales that surrounded Mendeleev and the table of chemical elements he created, M24.RU will tell in this article.
Table opening history
By the middle of the 19th century, 63 chemical elements had been discovered, and scientists around the world have repeatedly attempted to combine all the existing elements into a single concept. The elements were proposed to be placed in ascending order of atomic mass and divided into groups according to the similarity of chemical properties.
In 1863, the chemist and musician John Alexander Newland proposed his theory, who proposed a layout of chemical elements similar to that discovered by Mendeleev, but the work of the scientist was not taken seriously by the scientific community due to the fact that the author was carried away by the search for harmony and the connection of music with chemistry.
In 1869, Mendeleev published his scheme of the periodic table in the journal of the Russian Chemical Society and sent out a notice of the discovery to the leading scientists of the world. In the future, the chemist repeatedly refined and improved the scheme until it acquired its familiar form.
The essence of Mendeleev's discovery is that with an increase in the atomic mass, the chemical properties of elements do not change monotonously, but periodically. After a certain number of elements with different properties, the properties begin to repeat. Thus, potassium is similar to sodium, fluorine is similar to chlorine, and gold is similar to silver and copper.
In 1871, Mendeleev finally united the ideas into the Periodic Law. Scientists predicted the discovery of several new chemical elements and described their chemical properties. Subsequently, the chemist's calculations were fully confirmed - gallium, scandium and germanium fully corresponded to the properties that Mendeleev attributed to them.
Tales about Mendeleev
There were many tales about the famous scientist and his discoveries. People at that time had little idea of chemistry and believed that doing chemistry was something like eating soup from babies and stealing on an industrial scale. Therefore, the activities of Mendeleev quickly acquired a mass of rumors and legends.
One of the legends says that Mendeleev discovered the table of chemical elements in his sleep. The case is not the only one, August Kekule, who dreamed of the formula of the benzene ring, spoke in the same way about his discovery. However, Mendeleev only laughed at the critics. “I’ve been thinking about it for maybe twenty years, and you say: I was sitting in suddenly ... ready!”, The scientist once said about his discovery.
Another story credits Mendeleev with the discovery of vodka. In 1865, the great scientist defended his dissertation on the topic “Discourse on the combination of alcohol with water” and this immediately gave rise to a new legend. The contemporaries of the chemist laughed, saying that the scientist “does well under the influence of alcohol combined with water”, and the next generations already called Mendeleev the discoverer of vodka.
They also laughed at the way of life of the scientist, and especially at the fact that Mendeleev equipped his laboratory in the hollow of a huge oak.
Also, contemporaries teased Mendeleev's passion for suitcases. The scientist, at the time of his involuntary inaction in Simferopol, was forced to pass the time weaving suitcases. In the future, he independently made cardboard containers for the needs of the laboratory. Despite the clearly "amateur" nature of this hobby, Mendeleev was often called a "suitcase master."
Discovery of radium
One of the most tragic and at the same time famous pages in the history of chemistry and the appearance of new elements in the periodic table is associated with the discovery of radium. A new chemical element was discovered by the spouses Marie and Pierre Curie, who discovered that the waste remaining after the separation of uranium from uranium ore is more radioactive than pure uranium.
Since no one knew what radioactivity was then, the rumor quickly attributed healing properties and the ability to cure almost all diseases known to science to the new element. Radium was included in food products, toothpaste, face creams. The rich wore watches whose dial was painted with paint containing radium. The radioactive element was recommended as a means to improve potency and relieve stress.
Such "production" continued for twenty whole years - until the 30s of the twentieth century, when scientists discovered the true properties of radioactivity and found out how detrimental the effect of radiation on the human body.
Marie Curie died in 1934 from radiation sickness caused by long-term exposure to radium.
Nebulium and Coronium
The periodic table not only ordered the chemical elements into a single coherent system, but also made it possible to predict many discoveries of new elements. At the same time, some chemical "elements" were declared non-existent on the basis that they did not fit into the concept of the periodic law. The most famous story is the "discovery" of new elements of nebulium and coronium.
When studying the solar atmosphere, astronomers discovered spectral lines that they could not identify with any of the chemical elements known on earth. Scientists have suggested that these lines belong to a new element, which was called coronium (because the lines were discovered during the study of the "crown" of the Sun - the outer layer of the star's atmosphere).
A few years later, astronomers made another discovery by studying the spectra of gaseous nebulae. The discovered lines, which again could not be identified with anything terrestrial, were attributed to another chemical element - nebulium.
The discoveries were criticized, since Mendeleev's periodic table no longer had room for elements with the properties of nebulium and coronium. After checking, it was found that nebulium is ordinary terrestrial oxygen, and coronium is highly ionized iron.
The material was created on the basis of information from open sources. Prepared by Vasily Makagonov @vmakagonov
DISCOVERY OF THE PERIODIC LAW
The periodic law was discovered by D. I. Mendeleev while working on the text of the textbook "Fundamentals of Chemistry", when he encountered difficulties in systematizing the factual material. By mid-February 1869, thinking over the structure of the textbook, the scientist gradually came to the conclusion that the properties of simple substances and the atomic masses of elements are connected by a certain pattern.
The discovery of the periodic table of elements was not made by chance, it was the result of enormous work, long and painstaking work, which was spent both by Dmitry Ivanovich himself and by many chemists from among his predecessors and contemporaries. “When I began to finalize my classification of the elements, I wrote on separate cards each element and its compounds, and then, arranging them in the order of groups and rows, I received the first visual table of the periodic law. But this was only the final chord, the result of all previous work ... "- said the scientist. Mendeleev emphasized that his discovery was the result that completed twenty years of thinking about the relationships between elements, thinking from all sides of the relationship of elements.
On February 17 (March 1), the manuscript of the article, containing a table entitled "An experiment on a system of elements based on their atomic weight and chemical similarity," was completed and submitted for printing with notes for compositors and with the date "February 17, 1869." The report on the discovery of Mendeleev was made by the editor of the Russian Chemical Society, Professor N. A. Menshutkin, at a meeting of the society on February 22 (March 6), 1869. Mendeleev himself was not present at the meeting, since at that time, on the instructions of the Free Economic Society, he examined the cheese factories of Tverskaya and Novgorod provinces.
In the first version of the system, the elements were arranged by scientists in nineteen horizontal rows and six vertical columns. On February 17 (March 1), the discovery of the periodic law was by no means completed, but only began. Dmitry Ivanovich continued its development and deepening for almost three more years. In 1870, Mendeleev published the second version of the system (The Natural System of Elements) in Fundamentals of Chemistry: horizontal columns of analogous elements turned into eight vertically arranged groups; the six vertical columns of the first version turned into periods beginning with an alkali metal and ending with a halogen. Each period was divided into two rows; elements of different rows included in the group formed subgroups.
The essence of Mendeleev's discovery was that with an increase in the atomic mass of chemical elements, their properties do not change monotonously, but periodically. After a certain number of elements of different properties, arranged in ascending atomic weight, the properties begin to repeat. The difference between Mendeleev's work and the works of his predecessors was that Mendeleev had not one, but two bases for classifying elements - atomic mass and chemical similarity. In order for the periodicity to be fully respected, Mendeleev corrected the atomic masses of some elements, placed several elements in his system contrary to the then accepted ideas about their similarity with others, left empty cells in the table where elements that were not yet discovered should have been placed.
In 1871, on the basis of these works, Mendeleev formulated the Periodic Law, the form of which was somewhat improved over time.
The Periodic Table of the Elements had a great influence on the subsequent development of chemistry. It was not only the first natural classification of the chemical elements, which showed that they form a coherent system and are in close connection with each other, but was also a powerful tool for further research. At the time when Mendeleev compiled his table on the basis of the periodic law he had discovered, many elements were still unknown. Mendeleev was not only convinced that there must be elements yet unknown to fill these places, but he also predicted the properties of such elements in advance, based on their position among other elements of the periodic system. Over the next 15 years, Mendeleev's predictions were brilliantly confirmed; all three expected elements were discovered (Ga, Sc, Ge), which was the greatest triumph of the periodic law.
DI. Mendeleev handed over the manuscript "Experience of a system of elements based on their atomic weight and chemical similarity" // Presidential Library // A day in history http://www.prlib.ru/History/Pages/Item.aspx?itemid=1006
RUSSIAN CHEMICAL SOCIETY
The Russian Chemical Society is a scientific organization founded at St. Petersburg University in 1868 and was a voluntary association of Russian chemists.
The need to create the Society was announced at the 1st Congress of Russian Naturalists and Doctors, held in St. Petersburg in late December 1867 - early January 1868. At the Congress, the decision of the participants in the Chemical Section was announced:
The Chemistry Section declared a unanimous desire to unite in the Chemical Society for the communication of the already established forces of Russian chemists. The section believes that this society will have members in all cities of Russia, and that its publication will include the works of all Russian chemists, printed in Russian.
By this time, chemical societies had already been established in several European countries: the London Chemical Society (1841), the Chemical Society of France (1857), the German Chemical Society (1867); The American Chemical Society was founded in 1876.
The charter of the Russian Chemical Society, drawn up mainly by D. I. Mendeleev, was approved by the Ministry of Education on October 26, 1868, and the first meeting of the Society was held on November 6, 1868. Initially, it included 35 chemists from St. Petersburg, Kazan, Moscow, Warsaw , Kiev, Kharkov and Odessa. The first President of the RCS was N. N. Zinin, the secretary was N. A. Menshutkin. Members of the society paid membership fees (10 rubles per year), the admission of new members was carried out only on the recommendation of three existing ones. In the first year of its existence, the RCS grew from 35 to 60 members and continued to grow smoothly in subsequent years (129 in 1879, 237 in 1889, 293 in 1899, 364 in 1909, 565 in in 1917).
In 1869, the Russian Chemical Society got its own printed organ - the Journal of the Russian Chemical Society (ZhRHO); the magazine was published 9 times a year (monthly, except for the summer months). From 1869 to 1900, the editor of the ZhRHO was N. A. Menshutkin, and from 1901 to 1930 - A. E. Favorsky.
In 1878, the RCS merged with the Russian Physical Society (founded in 1872) to form the Russian Physical and Chemical Society. The first Presidents of RFHO were A. M. Butlerov (in 1878–1882) and D. I. Mendeleev (in 1883–1887). In connection with the merger, in 1879 (from the 11th volume) the Journal of the Russian Chemical Society was renamed into the Journal of the Russian Physical and Chemical Society. The periodicity of the publication was 10 issues per year; The journal consisted of two parts - chemical (LRHO) and physical (LRFO).
For the first time, many works of the classics of Russian chemistry were published on the pages of the ZhRHO. We can especially note the works of D. I. Mendeleev on the creation and development of the periodic system of elements and A. M. Butlerov, connected with the development of his theory of the structure of organic compounds; research by N. A. Menshutkin, D. P. Konovalov, N. S. Kurnakov, and L. A. Chugaev in the field of inorganic and physical chemistry; V. V. Markovnikov, E. E. Vagner, A. M. Zaitsev, S. N. Reformatsky, A. E. Favorsky, N. D. Zelinsky, S. V. Lebedev and A. E. Arbuzov in the field of organic chemistry. During the period from 1869 to 1930, 5067 original chemical studies were published in the ZhRHO, abstracts and review articles on certain problems of chemistry, and translations of the most interesting works from foreign journals were also published.
RFHO became the founder of the Mendeleev Congresses on General and Applied Chemistry; the first three congresses were held in St. Petersburg in 1907, 1911 and 1922. In 1919, the publication of the ZhRFKhO was suspended and resumed only in 1924.
