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. Not only was it 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 it was also a powerful tool for further research. At the time when Mendeleev compiled his table on the basis of the periodic law he 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 "The 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.
History of the discovery of the periodic law.
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 on studying cheese production from A. I. Khodnev, one of the leaders of the Free Economic Society.
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" (according to the old style ).
This is how 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 was then only 35 years old. 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.
Mendeleev still had a lot to do after the discovery of the Periodic Law. The reason for the periodic change in the properties of the elements remained unknown, and the very structure of the Periodic Table, where the properties were repeated through seven elements in the eighth, did not find an explanation. However, the first cover of mystery was removed from these numbers: in the second and third periods of the system, there were, then, just seven elements each.
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 atomic 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.
The most important thing in the discovery of the Periodic Law is the prediction of the existence of yet undiscovered chemical elements.
Under aluminum Al, Mendeleev left a place for its analogue "ekaaluminum", under boron B - for "ekabor", and under silicon Si - for "ekasilicon".
This is how Mendeleev called chemical elements that had not yet been discovered. He even gave them the symbols El, Eb and Es.
Regarding the element "ecasilicon", Mendeleev wrote: "It seems to me that the most interesting of the undoubtedly missing metals will be the one that belongs to the IV group of analogues of carbon, namely, to the III series. This will be the metal immediately following silicon, and therefore we will name his exacilitation." Indeed, this as yet undiscovered element was supposed to become a kind of "lock" connecting two typical non-metals - carbon C and silicon Si - with two typical metals - tin Sn and lead Pb.
Not all foreign chemists immediately appreciated the significance of Mendeleev's discovery. It changed a lot in the world of established ideas. Thus, the German physical chemist Wilhelm Ostwald, the future Nobel Prize winner, argued that it was not the law that was discovered, but the principle of classifying "something indefinite." The German chemist Robert Bunsen, who discovered two new alkaline elements in 1861, rubidium Rb and cesium Cs, wrote that Mendeleev was taking chemists "into a far-fetched world of pure abstractions."
Every year the Periodic Law won more and more supporters, and its discoverer - more and more recognition. High-ranking visitors began to appear in Mendeleev's laboratory, including even Grand Duke Konstantin Nikolayevich, head of the naval department.
Mendeleev accurately predicted the properties of ekaaluminum: its atomic mass, the density of the metal, the formula of oxide El 2 O 3 , chloride ElCl 3 , sulfate El 2 (SO 4) 3 . After the discovery of gallium, these formulas began to be written as Ga 2 O 3 , GaCl 3 and Ga 2 (SO 4) 3 .
Mendeleev predicted that it would be a very fusible metal, and indeed, the melting point of gallium turned out to be 29.8 °C. In terms of fusibility, gallium is second only to mercury Hg and cesium Cs.
In 1886, the professor of the Mining Academy in Freiburg, the German chemist Clemens Winkler, while analyzing the rare mineral argyrodite with the composition Ag 8 GeS 6, discovered another element predicted by Mendeleev. Winkler named the element he discovered germanium Ge in honor of his homeland, but for some reason this caused sharp objections from some chemists. They began to accuse Winkler of nationalism, of appropriating the discovery made by Mendeleev, who had already given the element the name "ecasilicon" and the symbol Es. Discouraged, Winkler turned to Dmitry Ivanovich himself for advice. He explained that it was the discoverer of the new element who should give it a name.
Mendeleev could not predict the existence of the group of noble gases, and at first they did not find a place in the Periodic system.
The discovery of argon Ar by the English scientists W. Ramsay and J. Rayleigh in 1894 immediately caused heated discussions and doubts about the Periodic Law and the Periodic Table of Elements. Mendeleev at first considered argon an allotropic modification of nitrogen and only in 1900, under the pressure of indisputable facts, agreed with the presence in the Periodic system of the "zero" group of chemical elements, which was occupied by other noble gases discovered after argon. Now this group is known under the number VIIIA.
In 1905, Mendeleev wrote: "Apparently, the future does not threaten the periodic law with destruction, but only promises superstructures and development, although as a Russian they wanted to erase me, especially the Germans."
The discovery of the Periodic Law accelerated the development of chemistry and the discovery of new chemical elements.
Structure of the periodic system:
periods, groups, subgroups.
So, we found out that the periodic system is a graphical expression of the periodic law.
Each element occupies a certain place (cell) in the periodic system and has its own ordinal (atomic) number. For example:
The horizontal rows of elements, within which the properties of the elements change sequentially, Mendeleev called periods(begin with an alkali metal (Li, Na, K, Rb, Cs, Fr) and end with a noble gas (He, Ne, Ar, Kr, Xe, Rn)). Exceptions: the first period, which begins with hydrogen, and the seventh period, which is incomplete. Periods are divided into small And large. Small periods are one horizontal row. The first, second and third periods are small, they contain 2 elements (1st period) or 8 elements (2nd, 3rd periods).
Large periods consist of two horizontal rows. The fourth, fifth and sixth periods are large, they contain 18 elements (4th, 5th periods) or 32 elements (6th, 7th periods). Top rows long periods are called even, the bottom rows are odd.
In the sixth period, the lanthanides and in the seventh period, the actinides are located at the bottom of the periodic table. In each period, from left to right, the metallic properties of the elements weaken, and the non-metallic properties increase. Only metals are found in even rows of long periods. As a result, the table has 7 periods, 10 rows and 8 vertical columns, named groups –
this is a set of elements that have the same highest valency in oxides and in other compounds. This valency is equal to the group number.
Exceptions:
In group VIII, only Ru and Os have the highest valency VIII.
Groups are vertical sequences of elements, they are numbered with Roman numerals from I to VIII and Russian letters A and B. Each group consists of two subgroups: main and secondary. The main subgroup - A, contains elements of small and large periods. The secondary subgroup, B, contains elements of only large periods. They include elements of periods starting from the fourth.
In the main subgroups, from top to bottom, the metallic properties are enhanced rather than the non-metallic properties are weakened. All elements of the secondary subgroups are metals.
At the gymnasium, D. I. Mendeleev studied mediocre at first. There are many satisfactory grades in the quarterly statements preserved in his archive, and there are more of them in the lower and middle grades. In high school, D. I. Mendeleev became interested in the physical and mathematical sciences, as well as in history and geography, he was also interested in the structure of the universe. Gradually, the success of the young schoolboy grew in the graduation certificate received on July 14, 1849. there were only two satisfactory marks: according to the law of God (a subject that he did not like) and in Russian literature (a good mark on this subject could not be, since Mendeleev did not know Church Slavonic well). The gymnasium left in the soul of D. I. Mendeleev many bright memories of teachers: about Pyotr Pavlovich Ershov - (author of the fairy tale “The Little Humpbacked Horse”), who was first a mentor, then director of the Tobolsk gymnasium; about I. K. Rummel - (teacher of physics and mathematics), who opened before him the ways of knowing nature. Summer 1850 went through trouble. First, D. I. Mendeleev submitted documents to the Medical and Surgical Academy, but he did not pass the first test - the presence in the anatomical theater. Mother suggested another way - to become a teacher. But in the Main Pedagogical Institute, recruitment was made a year later and just in 1850. there was no reception. Fortunately, the petition had an effect, He was enrolled in the institute on state support. Dmitry Ivanovich already in his second year was carried away by classes in laboratories, interesting lectures.
In 1855, D. I. Mendeleev brilliantly graduated from the institute with a gold medal. He was awarded the title of senior teacher. August 27, 1855 Mendeleev received documents on his appointment as a senior teacher in Simferopol. Dmitry Ivanovich works a lot: he teaches mathematics, physics, biology, physical geography. In two years, he published 70 articles in the Journal of the Ministry of National Education.
In April 1859, the young scientist Mendeleev was sent abroad "for improvement in the sciences." He meets with the Russian chemist N. N. Beketov, with the famous chemist M. Berthelot.
In 1860, D. I. Mendeleev participated in the first International Congress of Chemists in the German city of Karlsruhe.
In December 1861, Mendeleev became the rector of the university.
Mendeleev saw three circumstances that, in his opinion, contributed to the discovery of the periodic law:
First, the atomic weights of most of the known chemical elements have been 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 was studied, without knowledge of which it would be 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.
In September 1869 D. I. Mendeleev showed that the atomic volumes of simple substances are in a periodic dependence on atomic weights, and in October he discovered the valencies of elements in salt-forming oxides.
In the summer of 1870 Mendeleev found it necessary to change the incorrectly determined atomic weights of indium, cerium, yttrium, thorium, and uranium, and in connection with this he changed the placement of these elements in the system. So, uranium turned out to be the last element in the natural series, the heaviest in terms of atomic weight.
As new chemical elements were discovered, the need for their systematization was felt more and more acutely. In 1869, D. I. Mendeleev created the periodic system of elements and discovered the law underlying it. This discovery was a theoretical synthesis of all previous developments of the 10th century. : Mendeleev compared the physical and chemical properties of all the then known 63 chemical elements with their atomic weights and revealed the relationship between the two most important quantitatively measured properties of atoms, on which all chemistry was built - atomic weight and valence.
Many years later, Mendeleev described his system as follows: “This is the best set of my views and considerations on the periodicity of elements.” Mendeleev for the first time gave the canonical formulation of the periodic law, which existed before its physical justification: “The properties of the elements, and therefore the properties of the simple and complex bodies formed by them, stand in a periodic relationship with their atomic weight.
In less than six years, the news spread around the world: in 1875. The young French spectroscopist P. Lecoq de Boisbaudran isolated a new element from a mineral mined in the Pyrenees. Boisbaudran was traced by a faint violet line in the spectrum of the mineral, which could not be attributed to any of the known chemical elements. In honor of his homeland, which in ancient times was called Gaul, Boisbaudran named the new element gallium. Gallium is a very rare metal, and Boisbaudran had more difficulty in extracting it in quantities little more than a pinhead. What was Boisbaudran's surprise when, through the Paris Academy of Sciences, he received a letter with a Russian stamp, which stated: in the description of the properties of gallium, everything is correct, except for the density: gallium is heavier than water not 4.7 times, as Boisbaudran claimed, but 5, 9 times. Has anyone else discovered gallium before? Boisbaudran re-determined the density of gallium by subjecting the metal to a more thorough purification. And it turned out that he was mistaken, and the author of the letter - it was, of course, Mendeleev, who did not see gallium - was right: the relative density of gallium was not 4.7, but 5.9.
And 16 years after Mendeleev's prediction, the German chemist K. Winkler discovered a new element (1886) and named it germanium. This time, Mendeleev himself did not have to point out that this newly discovered element had also been predicted by him earlier. Winkler noted that germanium fully corresponds to Mendeleev's evasilience. Winkler wrote in his work: “It is hardly possible to find another more striking proof of the validity of the doctrine of periodicity, as in a newly discovered element. This is not just confirmation of a bold theory, here we see an obvious expansion of the chemical outlook, a powerful step in the field of knowledge.
The existence in nature of more than ten new elements unknown to anyone was predicted by Mendeleev himself. For a dozen elements, he predicted
correct atomic weight. All subsequent searches for new elements in nature were carried out by researchers using the periodic law and the periodic system. They not only helped scientists in their search for truth, but also contributed to the correction of errors and misconceptions in science.
Mendeleev's predictions were brilliantly justified - three new elements were discovered: gallium, scandium, germanium. The riddle of beryllium, which has long tormented scientists, has been resolved. Its atomic weight was finally precisely determined, and the place of the element next to lithium was confirmed once and for all. By the 90s of the 19th century. , according to Mendeleev, "periodic legality has been strengthened." In textbooks on chemistry in different countries, no doubt, Mendeleev's periodic system began to be included. The great discovery received universal recognition.
The fate of great discoveries is sometimes very difficult. On their way there are tests that sometimes even cast doubt on the truth of the discovery. So it was with the periodic table of elements.
It was associated with the unexpected discovery of a set of gaseous chemical elements, called inert or noble gases. The first of these is helium. Almost all reference books and encyclopedias date the discovery of helium in 1868. and associate this event with the French astronomer J. Jansen and the English astrophysicist N. Lockyer. Jansen was present at the total solar eclipse in India in August 1868. And his main merit is that he was able to observe solar prominences after the eclipse ended. They were observed only during an eclipse. Lockyer also observed prominences. Without leaving the British Isles, in mid-October of that year. Both scientists sent descriptions of their observations to the Paris Academy of Sciences. But since London is much closer to Paris than Calcutta, the letters almost simultaneously reached the addressee on October 26th. Not about any new element allegedly present on the Sun. There was not a word in these letters.
Scientists began to study in detail the spectra of prominences. And soon there were reports that they contain a line that cannot belong to the spectrum of any of the elements existing on Earth. In January 1869 the Italian astronomer A. Secchi designated it as. In such a record, it entered the history of science as a spectral "continent". On August 3, 1871, the physicist V. Thomson spoke publicly about the new solar element at the annual meeting of British scientists.
This is the true story of the discovery of helium in the Sun. For a long time, no one could say what this element is, what properties it has. Some scientists generally rejected the existence of helium on earth, since it could only exist at high temperatures. Helium was found on Earth only in 1895.
Such is the nature of the origin of the table of D. I. Mendeleev.
The approval of the atomic-molecular theory at the turn of the 119th - 19th centuries was accompanied by a rapid growth in the number of known chemical elements. In the first decade of the 19th century alone, 14 new elements were discovered. The record holder among the discoverers was the English chemist Humphry Davy, who in one year obtained 6 new simple substances (sodium, potassium, magnesium, calcium, barium, strontium) using electrolysis. And by 1830, the number of known elements reached 55.
The existence of such a number of elements, heterogeneous in their properties, puzzled chemists and required ordering and systematization of elements. Many scientists have been looking for patterns in the list of elements and have made some progress. There are three most significant works that challenged the priority of the discovery of the periodic law by D.I. Mendeleev.
Mendeleev formulated the periodic law in the form of the following main provisions:
- 1. Elements arranged by atomic weight represent a distinct periodicity of properties.
- 2. We must expect the discovery of many more unknown simple bodies, for example, elements similar to Al and Si with an atomic weight of 65 - 75.
- 3. The value of the atomic weight of an element can sometimes be corrected by knowing its analogies.
Some analogies are revealed by the magnitude of the weight of their atom. The first position was known even before Mendeleev, but it was he who gave it the character of a universal law, predicting on its basis the existence of yet undiscovered elements, changing the atomic weights of a number of elements and arranging some elements in the table contrary to their atomic weights, but in full accordance with their properties. (mainly valency). The remaining provisions were discovered only by Mendeleev and are logical consequences of the periodic law. The correctness of these consequences was confirmed by many experiments over the next two decades and made it possible to speak of the periodic law as a strict law of nature.
Using these provisions, Mendeleev compiled his version of the periodic table of elements. The first draft of the table of elements appeared on February 17 (March 1, according to the new style), 1869.
And on March 6, 1869, Professor Menshutkin made an official announcement of Mendeleev's discovery at a meeting of the Russian Chemical Society.
The following confession was put into the mouth of the scientist: I see a table in a dream, where all the elements are arranged as needed. I woke up, immediately wrote it down on a piece of paper - only in one place did it later turn out to be the necessary amendment. How simple everything is in legends! The development and correction took more than 30 years of the scientist's life.
The process of discovering the periodic law is instructive, and Mendeleev himself spoke about it this way: “The idea involuntarily arose that there must be a connection between mass and chemical properties.
And since the mass of a substance, although not absolute, but only relative, is finally expressed in the form of the weights of atoms, 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 is impossible to admit an accident.
In the very first periodic table, all elements up to and including calcium are the same as in the modern table, with the exception of noble gases. This can be seen from a page fragment from an article by D.I. Mendeleev, containing the periodic system of elements.
Based on the principle of increasing atomic weights, then the next elements after calcium should have been vanadium, chromium and titanium. But Mendeleev put a question mark after calcium, and then placed titanium, changing its atomic weight from 52 to 50.
The unknown element, indicated by a question mark, was assigned an atomic weight of A = 45, which is the arithmetic mean between the atomic weights of calcium and titanium. Then, between zinc and arsenic, Mendeleev left room for two elements that had not yet been discovered at once. In addition, he placed tellurium in front of iodine, although the latter has a lower atomic weight. With such an arrangement of elements, all horizontal rows in the table contained only similar elements, and the periodicity of changes in the properties of elements was clearly manifested. The next two years, Mendeleev significantly improved the system of elements. In 1871, the first edition of Dmitry Ivanovich's textbook "Fundamentals of Chemistry" was published, in which the periodic system is given in an almost modern form.
8 groups of elements were formed in the table, the group numbers indicate the highest valency of the elements of those series that are included in these groups, and the periods become closer to modern ones, divided into 12 series. Now each period begins with an active alkali metal and ends with a typical non-metal halogen. The second version of the system made it possible for Mendeleev to predict the existence of not 4, but 12 elements and, challenging the scientific world, described with amazing accuracy the properties of three unknown elements, which he called ekabor (eka on Sanskrit means "one and the same"), ekaaluminum and ekasilicon. (Gallia is the ancient Roman name for France). The scientist managed to isolate this element in its pure form and study its properties. And Mendeleev saw that the properties of gallium coincide with the properties of ekaaluminum predicted by him, and informed Lecoq de Boisbaudran that he had incorrectly measured the density of gallium, which should be equal to 5.9-6.0 g/cm3 instead of 4.7 g/cm3. Indeed, more accurate measurements led to the correct value of 5.904 g/cm3. The final recognition of the periodic law of D.I. Mendeleev achieved after 1886, when the German chemist K. Winkler, analyzing silver ore, received an element that he called germanium. It turns out to be an exacilium.
Periodic law and the periodic system of elements.
The periodic law is one of the most important laws of chemistry. Mendeleev believed that the main characteristic of an element is its atomic mass. Therefore, he arranged all the elements in one row in order of increasing their atomic mass.
If we consider a number of elements from Li to F, we can see that the metallic properties of the elements are weakened, and the non-metallic properties are enhanced. The properties of elements in the series from Na to Cl change similarly. The next sign K, like Li and Na, is a typical metal.
The highest valency of the elements increases from I y Li to V y N (oxygen and fluorine have constant valence II and I, respectively) and from I y Na to VII y Cl. The next element K, like Li and Na, has valence I. In the series of oxides from Li2O to N2O5 and hydroxides from LiOH to HNO3, the basic properties are weakened, and the acidic properties are enhanced. The properties of oxides change similarly in the series from Na2O and NaOH to Cl2O7 and HClO4. Potassium oxide K2O, like lithium and sodium oxides Li2O and Na2O, is a basic oxide, and potassium hydroxide KOH, like lithium and sodium hydroxides LiOH and NaOH, is a typical base.
The shapes and properties of nonmetals change similarly from CH4 to HF and from SiH4 to HCl.
This nature of the properties of elements and their compounds, which is observed with an increase in the atomic mass of elements, is called periodic change. The properties of all chemical elements change periodically with increasing atomic mass.
This periodic change is called the periodic dependence of the properties of elements and their compounds on the magnitude of the atomic mass.
Therefore, D.I. Mendeleev formulated the law he discovered as follows:
· The properties of the elements, as well as the forms and properties of the compounds of the elements are in a periodic dependence on the value of the atomic mass of the elements.
Mendeleev arranged the periods of the elements under each other and as a result compiled the periodic table of elements.
He said that the table of elements was the fruit not only of his own work, but also of the efforts of many chemists, among whom he especially noted the "strengtheners of the periodic law" who discovered the elements he predicted.
To create a modern table, it took many years of hard work of thousands and thousands of chemists and physicists. If Mendeleev were alive now, he, looking at the modern table of elements, could well repeat the words of the English chemist JW Mellor, the author of the classic 16-volume encyclopedia on inorganic and theoretical chemistry. Having finished his work in 1937, after 15 years of work, he wrote with gratitude on the title page: “Dedicated to the rank and file of a huge army of chemists. Their names are forgotten, their works remain"...
The periodic system is a classification of chemical elements that establishes the dependence of various properties of elements on the charge of the atomic nucleus. The system is a graphical expression of the periodic law. As of October 2009, 117 chemical elements are known (with serial numbers from 1 to 116 and 118), of which 94 are found in nature (some are only in trace amounts). The rest23 were obtained artificially as a result of nuclear reactions - this is the process of transformation of atomic nuclei, which occurs when they interact with elementary particles, gamma quanta and with each other, usually leading to the release of an enormous amount of energy. The first 112 elements have permanent names, the rest are temporary.
The discovery of the 112th element (the heaviest of the official ones) is recognized by the International Union of Theoretical and Applied Chemistry.
The most stable known isotope of this element has a half-life of 34 seconds. At the beginning of June 2009, it bears the unofficial name ununbium, and was first synthesized in February 1996 at the heavy ion accelerator at the Heavy Ion Institute in Darmstadt. The discoverers have half a year to propose a new official name to add to the table (they have already proposed Wickshausius, Helmholtius, Venusius, Frisch, Strassmanius and Heisenberg). At present, transuranium elements with numbers 113-116 and 118, obtained at the Joint Institute for Nuclear Research in Dubna, are known, but they have not yet been officially recognized. More common than others are 3 forms of the periodic table: “short” (short-period), “long” (long-period) and “extra-long”. In the "extra-long" version, each period occupies exactly one line. In the "long" version, lanthanides (a family of 14 chemical elements with serial numbers 58--71, located in the VI period of the system) and actinides (a family of radioactive chemical elements, consisting of actinium and 14 similar in their chemical properties) are taken out of the general table making it more compact. In the "short" form of entry, in addition to this, the fourth and subsequent periods occupy 2 lines; the symbols of the elements of the main and secondary subgroups are aligned relative to different edges of the cells. The short form of the table containing eight groups of elements was officially abolished by IUPAC in 1989. Despite the recommendation to use the long form, the short form continued to be given in a large number of Russian reference books and manuals after that time. From modern foreign literature, the short form is completely excluded; instead, the long form is used. Some researchers associate this situation, among other things, with the seemingly rational compactness of the short form of the table, as well as with stereotyped thinking and a lack of perception of modern (international) information.
In 1969, Theodor Seaborg proposed an extended periodic table of elements. Niels Bohr developed the ladder (pyramidal) form of the periodic system.
There are many other, rarely or not used at all, but very original, ways to graphically display the Periodic Law. Today, there are several hundred versions of the table, while scientists offer more and more new options.
Periodic law and its justification.
The periodic law made it possible to bring into the system and generalize a huge amount of scientific information in chemistry. This function of the law is called integrative. It manifests itself especially clearly in the structuring of the scientific and educational material of chemistry.
Academician A.E. Fersman said that the system united all chemistry within the framework of a single spatial, chronological, genetic, energy connection.
The integrative role of the Periodic Law was also manifested in the fact that some data on the elements, allegedly falling out of general patterns, were verified and refined both by the author himself and by his followers.
This happened with the characteristics of beryllium. Prior to Mendeleev's work, it was considered a trivalent analogue of aluminum due to their so-called diagonal similarity. Thus, in the second period there were two trivalent elements and not a single divalent element. It was at this stage that Mendeleev suspected a mistake in researching the properties of beryllium, he found the work of the Russian chemist Avdeev, who claimed that beryllium is divalent and has an atomic weight of 9. Avdeev’s work remained unnoticed by the scientific world, the author died early, apparently having been poisoned with extremely poisonous beryllium compounds. The results of Avdeev's research were established in science thanks to the Periodic Law.
Such changes and refinements of the values of both atomic weights and valences were made by Mendeleev for nine more elements (In, V, Th, U, La, Ce and three other lanthanides).
Ten more elements had only atomic weights corrected. And all these refinements were subsequently confirmed experimentally.
The prognostic (predictive) function of the Periodic Law received the most striking confirmation in the discovery of unknown elements with serial numbers 21, 31 and 32.
Their existence was first predicted on an intuitive level, but with the formation of the system, Mendeleev was able to calculate their properties with a high degree of accuracy. The well-known story of the discovery of scandium, gallium and germanium was the triumph of Mendeleev's discovery. He made all his predictions on the basis of the universal law of nature discovered by himself.
In total, twelve elements were predicted by Mendeleev. From the very beginning, Mendeleev pointed out that the law describes the properties not only of the chemical elements themselves, but also of many of their compounds. It suffices to give an example to confirm this. Since 1929, when Academician P. L. Kapitsa first discovered the non-metallic conductivity of germanium, the development of the theory of semiconductors began in all countries of the world.
It immediately became clear that elements with such properties occupy the main subgroup of group IV.
Over time, the understanding came that compounds of elements located in periods equally distant from this group (for example, with a general formula like AzB) should have semiconductor properties to a greater or lesser extent.
This immediately made the search for new practically important semiconductors purposeful and predictable. Almost all modern electronics is based on such connections.
It is important to note that predictions within the framework of the Periodic System were made even after its universal recognition. In 1913
Moseley discovered that the wavelength of X-rays, which are obtained from anticathodes made from different elements, varies regularly depending on the ordinal number conventionally assigned to the elements in the Periodic Table. The experiment confirmed that the atomic number of an element has a direct physical meaning.
Only later were serial numbers associated with the value of the positive charge of the nucleus. On the other hand, Moseley's law made it possible to immediately experimentally confirm the number of elements in periods and, at the same time, to predict the places of hafnium (No. 72) and rhenium (No. 75) that had not yet been discovered by that time.
For a long time there was a dispute: to separate inert gases into an independent zero group of elements or to consider them the main subgroup of group VIII.
Based on the position of the elements in the Periodic Table, theoretical chemists led by Linus Pauling have long doubted the complete chemical passivity of inert gases, directly pointing to the possible stability of their fluorides and oxides.
But only in 1962, the American chemist Neil Bartlett for the first time carried out the reaction of platinum hexafluoride with oxygen under the most ordinary conditions, obtaining xenon hexafluoroplatinate XePtF ^, and after it other gas compounds, which are now more correctly called noble, and not inert.
The discovery by Dmitri Mendeleev of the periodic table of chemical elements in March 1869 was a real breakthrough in chemistry. The Russian scientist managed to systematize knowledge about chemical elements and present them in the form of a table, which schoolchildren still study in chemistry classes now. The periodic table became the foundation for the rapid development of this complex and interesting science, and the history of its discovery is shrouded in legends and myths. For all those who are fond of science, it will be interesting to know the truth about how Mendeleev discovered the table of periodic elements.
The history of the periodic table: how it all began
Attempts to classify and systematize known chemical elements were made long before Dmitri Mendeleev. Their systems of elements were proposed by such famous scientists as Debereiner, Newlands, Meyer and others. However, due to the lack of data on the chemical elements and their correct atomic masses, the proposed systems were not entirely reliable.
The history of the discovery of the periodic table begins in 1869, when a Russian scientist at a meeting of the Russian Chemical Society told his colleagues about his discovery. In the table proposed by the scientist, the chemical elements were arranged depending on their properties, provided by the value of their molecular weight.
An interesting feature of the periodic table was also the presence of empty cells, which in the future were filled with discovered chemical elements predicted by the scientist (germanium, gallium, scandium). After the discovery of the periodic table, additions and amendments were made to it many times. Together with the Scottish chemist William Ramsay, Mendeleev added a group of inert gases (zero group) to the table.
In the future, the history of Mendeleev's periodic table was directly related to discoveries in another science - physics. Work on the table of periodic elements is still ongoing, with modern scientists adding new chemical elements as they are discovered. The importance of the periodic system of Dmitri Mendeleev is difficult to overestimate, because thanks to it:
- Knowledge about the properties of already discovered chemical elements was systematized;
- It became possible to predict the discovery of new chemical elements;
- Such branches of physics as the physics of the atom and the physics of the nucleus began to develop;
There are many options for depicting chemical elements according to the periodic law, but the most famous and common option is the periodic table familiar to everyone.
Myths and facts about the creation of the periodic table
The most common misconception in the history of the discovery of the periodic table is that the scientist saw it in a dream. In fact, Dmitri Mendeleev himself refuted this myth and stated that he had been thinking about the periodic law for many years. To systematize the chemical elements, he wrote each of them on a separate card and repeatedly combined them with each other, arranging them in rows depending on their similar properties.
The myth about the "prophetic" dream of a scientist can be explained by the fact that Mendeleev worked on the systematization of chemical elements for days on end, interrupted by a short sleep. However, only the hard work and natural talent of the scientist gave the long-awaited result and provided Dmitri Mendeleev with worldwide fame.
Many students at school, and sometimes at the university, are forced to memorize or at least roughly navigate the periodic table. To do this, a person must not only have a good memory, but also think logically, linking elements into separate groups and classes. Studying the table is easiest for those people who constantly keep their brain in good shape by taking trainings on BrainApps.
