Opening history:
Predicted (as "eka-iodine") by D. I. Mendeleev in 1898. “... upon discovery of a halogen X with an atomic weight greater than iodine, it will still form KX, KXO3, etc., that its hydrogen compound HX will be a gaseous, very fragile acid, that the atomic weight will be ... 215”
Astatine was first obtained artificially in 1940 by D. Corson, C. R. Mackenzie, and E. Segre (University of California at Berkeley). To synthesize the 211 At isotope, they irradiated bismuth with alpha particles. In 1943-1946, astatine isotopes were discovered in the composition of natural radioactive series.
The name Astatium is derived from the Greek. words ( astatoz) meaning "unstable".
Receipt:
Short-lived astatine radionuclides (215 At, 218 At and 219 At) are formed during the radioactive decay of 235 U and 238 U, this is due to the constant presence of traces of astatine in nature (~ 1 g). Basically, astatine isotopes are obtained by irradiating metallic bismuth or thorium. a- high-energy particles with subsequent separation of astatine by co-precipitation, extraction, chromatography or distillation. The mass number of the most stable known isotope is 210.
Physical properties:
Due to its strong radioactivity, it cannot be obtained in macroscopic quantities sufficient for a deep study of its properties. According to calculations, the simple substance astatine under normal conditions is unstable dark blue crystals, consisting not of At 2 molecules, but of individual atoms. Melting point is about 230-240°C, boiling (sublimation) - 309°C.
Chemical properties:
In terms of chemical properties, astatine is close to both iodine (shows the properties of halogens) and polonium (metal properties).
Astatine in aqueous solution is reduced by sulfur dioxide; like metals, it is precipitated even from strongly acidic solutions by hydrogen sulfide, and is displaced from sulfuric acid solutions by zinc.
Like all halogens (except fluorine), astatine forms an insoluble salt of AgAt (silver astatide). It is able to oxidize to the state At (V), like iodine (for example, AgAtO 3 salt is identical in properties to AgIO 3). Astatine reacts with bromine and iodine to form interhalogen compounds - astatine iodide AtI and astatine bromide AtBr.
When an aqueous solution of astatine is exposed to hydrogen, gaseous hydrogen astatide HAt is formed at the time of the reaction, the substance is extremely unstable.
Application:
The instability of astatine makes the use of its compounds problematic, however, the possibility of using various isotopes of this element to combat cancer has been studied. See also: Astatine // Wikipedia. . Date of update: 05/02/2018. URL: https://ru.wikipedia.org/?oldid=92423599 (date of access: 08/02/2018).
The discovery of the elements and the origin of their names.
There are 94 chemical elements found in nature. To date, another 15 transuranium elements (elements 95 to 109) have been artificially obtained, the existence of 10 of them is indisputable.
The most common
Lithosphere. Oxygen (O), 46.60% by weight. Opened in 1771 by Karl Scheele (Sweden).
Atmosphere. Nitrogen (N), 78.09% by volume, 75.52% by mass. Opened in 1772 by Rutherford (Great Britain).
Universe. Hydrogen (H), 90% of the total substance. Opened in 1776 by Henry Cavendish (Great Britain).
The rarest (out of 94)
Lithosphere. Astatine (At): 0.16 g in the earth's crust. Opened in 1940 by Corson (USA) with employees. The naturally occurring isotope astatine 215 (215 At) (discovered in 1943 by B. Karlik and T. Bernert, Austria) exists in an amount of only 4.5 nanograms.
Atmosphere. Radon (Rn): only 2.4 kg (6 10 -20 volume of one part per 1 million). Opened in 1900 by Dorn (Germany). The concentration of this radioactive gas in the areas of deposits of granite rocks has allegedly caused a number of cancers. The total mass of radon located in the earth's crust, from which atmospheric gas reserves are replenished, is 160 tons.
The easiest
Gas. Hydrogen (H) has a density of 0.00008989 g/cm 3 at a temperature of 0°C and a pressure of 1 atm. Discovered in 1776 by Cavendish (Great Britain).
Metal. Lithium (Li), having a density of 0.5334 g/cm3, is the lightest of all solids. Discovered in 1817 by Arfvedson (Sweden).
Maximum Density
Osmium (Os), having a density of 22.59 g/cm3, is the heaviest of all solids. Opened in 1804 by Tennant (Great Britain).
The heaviest gas
It is radon (Rn), the density of which is 0.01005 g/cm 3 at 0°C. Opened in 1900 by Dorn (Germany).
Last received
Element 108, or unnilocty (Uno). This provisional name is given by the International Union of Pure and Applied Chemistry (IUPAC). Obtained in April 1984 by G. Münzenberg and colleagues (West Germany), who observed only 3 atoms of this element in the laboratory of the Society for the Study of Heavy Ions in Darmstadt. In June of the same year, a message appeared that this element was also received by Yu.Ts. Oganesyan with collaborators at the Joint Institute for Nuclear Research, Dubna, USSR.
A single unionium atom (Une) was obtained by bombarding bismuth with iron ions in the laboratory of the Society for the Study of Heavy Ions, Darmstadt, West Germany, on August 29, 1982. It has the largest serial number (element 109) and the largest atomic mass (266) . According to the most preliminary data, Soviet scientists observed the formation of an isotope of element 110 with an atomic mass of 272 (tentative name - ununnylium (Uun)).
The cleanest
Helium-4 (4He), obtained in April 1978 by P.V. McLintock of Lancaster University, USA, has less than 2 parts of impurities per 10 15 parts by volume.
The hardest
Carbon (C). In its allotropic form, the diamond has a Knoop hardness of 8400. It has been known since prehistoric times.
Dearest
Californium (Cf) was sold in 1970 for $10 per microgram. Opened in 1950 by Seaborg (USA) with employees.
The most plastic
Gold (Au). From 1 g it is possible to draw a wire 2.4 km long. Known since 3000 BC
Highest tensile strength
Boron (B) - 5.7 GPa. Opened in 1808 by Gay-Lussac and Tenard (France) and X. Davy (Great Britain).
Melting/boiling point
Lowest. Among non-metals, helium-4 (4He) has the lowest melting point of -272.375°C at a pressure of 24.985 atm and the lowest boiling point of -268.928°C. Helium was discovered in 1868 by Lockyer (Great Britain) and Jansen (France). Monatomic hydrogen (H) must be an incompressible superfluid gas. Among metals, the corresponding parameters for mercury (Hg) are –38.836°C (melting point) and 356.661°C (boiling point).
The tallest. Among non-metals, the highest melting point and boiling point of carbon known from prehistoric times (C): 530 ° C and 3870 ° C. However, it seems debatable that graphite is stable at high temperatures. Passing at 3720°C from a solid to a vapor state, graphite can be obtained as a liquid at a pressure of 100 atm and a temperature of 4730°C. Among metals, the corresponding parameters for tungsten (W): 3420°C (melting point) and 5860°C (boiling point). Opened in 1783 H.Kh. and F. d "Eluyarami (Spain).
isotopes
The largest number of isotopes (36 each) is found in xenon (Xe), discovered in 1898 by Ramsay and Travers (Great Britain), and in cesium (Cs), discovered in 1860 by Bunsen and Kirchhoff (Germany). The smallest amount (3: protium, deuterium and tritium) in hydrogen (H), discovered in 1776 by Cavendish (Great Britain).
The most stable. Tellurium-128 (128 Te), according to double beta decay, has a half-life of 1.5 10 24 years. Tellurium (Te) was discovered in 1782 by Müller von Reichenstein (Austria). The isotope 128 Te was first discovered in the natural state in 1924 by F. Aston (Great Britain). The data on its superstability were again confirmed in 1968 by the studies of E. Alexander Jr., B. Srinivasan and O. Manuel (USA). The alpha decay record belongs to samarium-148 (148 Sm) - 8 10 15 years. The beta decay record belongs to the cadmium isotope 113 (113 Cd) - 9 10 15 years. Both isotopes were discovered in their natural state by F. Aston, respectively, in 1933 and 1924. The radioactivity of 148 Sm was discovered by T. Wilkins and A. Dempster (USA) in 1938, and the radioactivity of 113 Cd was discovered in 1961 by D. Watt and R. Glover (Great Britain).
Most unstable. The lifetime of lithium-5 (5 Li) is limited to 4.4 10 -22 s. The isotope was first discovered by E. Titterton (Australia) and T. Brinkley (Great Britain) in 1950.
Liquid range
Considering the difference between melting point and boiling point, the element with the shortest liquid series is the inert gas neon (Ne) at only 2.542 degrees (-248.594°C to -246.052°C), while the longest liquid series (3453 degrees) characteristic of the radioactive transuranic element neptunium (Np) (from 637°C to 4090°C). However, if we take into account the true series of liquids - from the melting point to the critical point, then the element helium (He) has the shortest period - only 5.195 degrees (from absolute zero to -268.928 ° C), and the longest - 10200 degrees - for tungsten (from 3420°С to 13620°С).
The most poisonous
Among non-radioactive substances, the most stringent restrictions are set for beryllium (Be) - the maximum permissible concentration (MPC) of this element in the air is only 2 μg / m 3. Among the radioactive isotopes that exist in nature or produced by nuclear installations, the most stringent limits on the content in the air are set for thorium-228 (228 Th), which was first discovered by Otto Hahn (Germany) in 1905 (2.4 10 -16 g / m 3), and in terms of content in water - for radium-228 (228 Ra), discovered by O. Gan in 1907 (1.1 10 -13 g / l). From an ecological point of view, they have significant half-lives (i.e. over 6 months).
Guinness World Records, 1998
Astat), At, non-metallic radioactive chemical element, atomic number 85, atomic mass 210.1. General description
Has isotopes with at. V. 202-219, of which At 211 (7.5 hours) and At 210 (8.3 hours) have the most half-lives. A. is not found in nature; it was first obtained artificially by bombarding Bismuth with α-particles. A. for chem. properties similar to halogens and to metals.
2. History
Astatine was first obtained artificially in 1940 by D. Corson, K. R. Mackenzie, and E. Segre (University of California at Berkeley). To synthesize the 211 At isotope, they irradiated bismuth with alpha particles.
In 1943 - 1946 isotopes of astatine were discovered in the composition of natural radioactive elements.
3. Origin of the name
Melting point 302? C, boiling (sublimation) 337 ? C.
6.2. Chemical properties
In terms of properties, astatine resembles iodine in everything: it is distilled, extracted with carbon tetrachloride CCl 4 from aqueous solutions, reduced with zinc or sulfur dioxide to the astatide ion At -:
,which with silver ions forms insoluble silver astatide AgAt. The latter is quantitatively spiked with silver iodide as a carrier. Astatate Ion AtO - 3 is formed during the oxidation of the astatide ion with iodic acid H 5 IO 6 or cerium Ce (IV):
The formalized record of this equation corresponds to the condition of electroneutrality. In fact, Ce (IV) ions exist in the form of hydrated ions 4, which form a hydrogen ion and, with the exception of very acidic solutions (pH ~ 1), then undergo hydrolysis and polymerization. Ions AtO 3 - quantitatively precipitate with water-insoluble Pb (IO 3) 2.
Astatine (from other Greek ἄστατος - “unstable”) is an element of the 17th group of the periodic table of chemical elements (according to the outdated classification, an element of the main subgroup of group VII), of the sixth period, with atomic number 85. It is designated by the symbol At (lat. astatium).
Radioactive. A simple substance astatine (CAS number: 7440-68-8) under normal conditions - unstable crystals of black-blue color. The astatine molecule is apparently diatomic (formula At 2).
Story
Predicted (as "eka-iodine") by D. I. Mendeleev. In 1931, F. Allison and coworkers (Alabama Polytechnic Institute) reported the discovery of this element in nature and proposed the name alabamine (Ab) for it, but this result was not confirmed. Astatine was first obtained artificially in 1940 by D. Corson, C. R. Mackenzie, and E. Segre (University of California at Berkeley). To synthesize the 211 At isotope, they irradiated bismuth with alpha particles.
In 1943-1946, astatine isotopes were discovered in the composition of natural radioactive series.
In Russian terminology, the element was called "astatine" until 1962.
The names "Helvetin" (in honor of Helvetia - the ancient name of Switzerland) and "leptin" (from the Greek "weak, shaky") were also proposed.
Receipt
Astatine is obtained only artificially. Basically, astatine isotopes are obtained by irradiating metallic bismuth or thorium with high-energy α-particles, followed by separation of astatine by co-precipitation, extraction, chromatography or distillation.
Physical properties
Due to the small amount of matter available for study, the physical properties of this element are poorly understood and, as a rule, are built on analogies with more accessible elements.
Astatine is a blue-black solid, similar in appearance to iodine. It is characterized by a combination of properties of non-metals (halogens) and metals (polonium, lead and others). Like iodine, astatine dissolves well in organic solvents and is easily extracted by them. In terms of volatility, it is slightly inferior to iodine, but it can also easily sublimate.
Melting point 302 °C, boiling point (sublimation) 337 °C.
Chemical properties
Halogen. In positive oxidation states, astatine forms an oxygen-containing form, which is conventionally designated as At τ+ (astatine-tau-plus).
When an aqueous solution of astatine is exposed to hydrogen, gaseous hydrogen astatide HAt is formed at the time of the reaction. Astatine in aqueous solution is reduced by SO 2 and oxidized by Br 2 . Astatine, like metals, precipitates from hydrochloric acid solutions with hydrogen sulfide (H 2 S). Displaced from the solution by zinc (metal properties).
Interhalogen compounds of astatine are also known - astatine iodide AtI and astatine bromide AtBr. Hydrogen astatide HAt has also been obtained.
However, due to the same electronegativity of hydrogen and astatine, astatine is extremely unstable, and in aqueous solutions there are not only protons, but also At + ions, which is not the case for all other hydrohalic acids.
With metals, astatine forms compounds in which it exhibits an oxidation state of −1, like all other halogens (NaAt, for example, is called sodium astatide). Like other halogens, astatine can replace hydrogen in a methane molecule to produce tetraastatmethane CAt 4 . In this case, astatmethane, diastatmethane, astatoform are formed first.
Astatine, the fifth halogen, is the least common element on our planet, except, of course, for the transuranium elements. An approximate calculation shows that the entire earth's crust contains only about 30 g of astatine, and this estimate is the most optimistic. Element No. 85 has no stable isotopes, and the longest-lived radioactive isotope has a half-life of 8.3 hours, i.e. not even half of the astatine received in the morning remains by the evening.
Thus, the name astatine - and in Greek αστατος means "unstable" - successfully reflects the nature of this element. What then can astatine be interesting for and is it worth studying it? It is worth it, because astatine (just like promethium, technetium and francium) was created by man in the full sense of the word, and the study of this element gives a lot of instructive information - primarily for understanding the patterns in changing the properties of the elements of the periodic system. Showing metallic properties in some cases, and non-metallic properties in others, astatine is one of the most peculiar elements.
Until 1962, in the Russian chemical literature, this element was called astatine, and now the name “astatine” has stuck to it, and this is apparently correct: neither in the Greek nor in the Latin name of this element (in Latin astatium) is there a suffix “in ".
The search for ecaiod
D. I. Mendeleev called the last halogen not only ecaiod, but also halogen X. He wrote in 1898: KX, KXO 3, etc., that its hydrogen compound will be a gaseous, very unstable acid, that the atomic one will be ... about 215.
In 1920, the German chemist E. Wagner again drew attention to the still hypothetical fifth member of the halogen group, arguing that this element must be radioactive.
Then an intensive search for element No. 85 in natural objects began.
In assumptions about the properties of the 85th element, chemists proceeded from its location in the periodic system and from data on the properties of the neighbors of this element according to the periodic table. Considering the properties of other members of the halogen group, it is easy to notice the following pattern: fluorine and chlorine are gases, bromine is already a liquid, and iodine is a solid substance that exhibits, albeit to a small extent, the properties of metals. Ecaiodine is the heaviest halogen. Obviously, it must be even more metal-like than iodine, and, having many of the properties of halogens, one way or another similar to its neighbor on the left - polonium ... Together with other halogens, ecaiodus, apparently, should be in the water of the seas, oceans , boreholes. They tried to look for it, like iodine, in seaweed, brines, etc. The English chemist I. Friend tried to find the current astatine and francium in the waters of the Dead Sea, in which, as was known, both halogens and alkali metals are more than enough. To extract ecaiodine from a solution of chlorides, silver chloride was precipitated; Friend believed that the sediment would also carry away traces of the 85th element. However, neither X-ray spectral analysis nor mass spectrometry gave a positive result.
In 1932, chemists at the Alabama Polytechnic Institute (USA), headed by F. Allison, reported that they had isolated a product from monazite sand that contained about 0.000002 g of one of the compounds of element No. 85. In honor of their state, they named it "alabamium" and even described its combination with hydrogen and oxygen-containing acids. The name alabamium for element 85 appeared in chemistry textbooks and reference books until 1947.
However, soon after this message, several scientists had doubts about the reliability of Allison's discovery. The properties of alabamium diverged sharply from the predictions of the periodic law. In addition, by this time it became clear that all elements heavier than bismuth do not have stable isotopes. Assuming the stability of element No. 85, science would be faced with an inexplicable anomaly. Well, if element No. 85 is not stable, then it can be found on Earth only in two cases: if it has an isotope with a half-life greater than the age of the Earth, or if its isotopes are formed during the decay of long-lived radioactive elements.
The suggestion that element 85 could be a radioactive decay product of other elements became the starting point for another large group of researchers looking for ecaiod. The first in this group should be called the famous German radiochemist Otto Hahn, who as early as 1926 suggested the possibility of the formation of isotopes of the 85th element during the beta decay of polonium.
For 19 years, from 1925 to 1943, at least half a dozen reports about the discovery of ecaiod appeared in the periodical press. He was credited with certain chemical properties, given sonorous names: Helvetium (in honor of Switzerland), Anglo-Helvetium (in honor of England and Switzerland), Dakin (from the name of the ancient country of the Dacians in Central Europe), Leptin (translated from Greek “weak”, “shaky ”, “dispossessed”), etc. However, the first reliable message about the discovery and identification of element No. 85 was made by physicists involved in the synthesis of new elements.
At the University of California cyclotron, D. Corson, C. McKenzie, and E. Segre irradiated a bismuth target with alpha particles. The energy of the particles was 21 MeV, and the nuclear reaction for obtaining element #85 was as follows:
209 83 Bi + 4 2 He → 211 85 At + 2 1 0 n.
The new synthetic element was named only after the war, in 1947. But even earlier, in 1943, it was proved that astatine isotopes are formed in all three rows of radioactive decay. Therefore, astatine is found in nature.
Astatine in nature
Astatine in nature was the first to be found by Austrian chemists B. Karlik and T. Bernert. Studying the radioactivity of the daughter products of radon, they found that a small part of radium-A (the so-called then, and still called, the 218 Po isotope) decays in two ways (the so-called radioactive fork):
In a freshly isolated sample of RaA, along with alpha particles generated by polonium-218, alpha particles with other characteristics were also detected. Just such particles could, according to theoretical estimates, emit nuclei of the isotope 218 85.
Later, short-lived isotopes 215 At, 216 At, and 217 At were discovered in other experiments. And in 1953, the American radiochemists E. Hyde and A. Ghiorso isolated the 219 At isotope from francium-223 by chemical means. This is the only case of chemical identification of an isotope of astatine from a naturally occurring isotope. It is much easier and more convenient to obtain astatine artificially.
discover, identify, find out
The above reaction of irradiation of bismus with alpha particles can also be used for the synthesis of other isotopes of astatine. It is enough to increase the energy of the bombarding particles to 30 MeV, as the reaction proceeds with the emission of three neutrons and astatine-210 is formed instead of astatine-211. The higher the energy of alpha particles, the more secondary neutrons are produced and the smaller, consequently, the mass number of the resulting isotope. As targets for irradiation, metallic bismuth or its oxide is used, which is deposited or deposited onto an aluminum or copper substrate.
Rice. 6.
Another method for the synthesis of astatine is to irradiate a gold target with accelerated carbon ions. In this case, in particular, the following reaction occurs:
197 79 Au + 12 6 C → 205 85 At + 4 1 0 n.
To isolate the resulting astatine from bismuth or gold targets, a rather high volatility of astatine is used - it is still a halogen! Distillation occurs in a stream of nitrogen or in vacuum when the target is heated to 300...600°C. Astatine condenses on the surface of a glass trap cooled with liquid nitrogen or dry ice.
Another way to obtain astatine is based on the reactions of fission of uranium or thorium nuclei when they are irradiated with alpha particles or high-energy protons. So, for example, when 1 g of metallic thorium is irradiated with protons with an energy of 680 MeV at the synchrocyclotron of the Joint Institute for Nuclear Research in Dubna, about 20 microcuries (otherwise 3 10 13 atoms) of astatine are obtained. However, in this case it is much more difficult to isolate astatine from a complex mixture of elements. This difficult problem was solved by a group of radiochemists from Dubna headed by V.A. Khalkin.
Now 20 isotopes of astatine with mass numbers from 200 to 219 are already known. The longest-lived of them is the 210 At isotope (half-life 8.3 hours), and the shortest-lived is 214 At (2 10 -6 seconds).
Since astatine cannot be obtained in significant quantities, its physical and chemical properties are not fully understood, and physicochemical constants are most often calculated by analogy with more accessible neighbors in the periodic system. In particular, the melting and boiling points of astatine were calculated as 411 and 299°C, i.e. astatine, like iodine, should sublime more easily than melt.
All studies on the chemistry of astatine were carried out with ultra-small amounts of this element, on the order of 10–9 ... 10–13 g per liter of solvent. And the point is not even that it is impossible to obtain more concentrated solutions. If they could be obtained, it would be extremely difficult to work with them. The alpha radiation of astatine leads to the radiolysis of solutions, their strong heating and the formation of large amounts of by-products.
And yet, despite all these difficulties, despite the fact that the number of astatine atoms in solution is comparable to random (albeit carefully avoided) pollution, some progress has been made in studying the chemical properties of astatine. It has been established that astatine can exist in six valence states - from 1 - to 7+. In this, it manifests itself as a typical analogue of iodine. Like iodine, it dissolves well in most organic solvents, but it acquires a positive electric charge more easily than iodine.
The properties of a number of interhalogen compounds of astatine, for example, AtBr, AtI, CsAtI 2 , have been obtained and studied.
An attempt with suitable means
The first attempts to apply astatine in practice were made as early as 1940, immediately after obtaining this element. A group of employees at the University of California found that astatine, like iodine, is selectively concentrated in the thyroid gland. Experiments have shown that the use of 211 At for the treatment of thyroid diseases is more beneficial than radioactive 131 I.
Astatine-211 emits only alpha rays - very energetic at short distances, but not able to go far. As a result, they act only on the thyroid gland, without affecting the neighboring - parathyroid. The radiobiological effect of astatine alpha particles on the thyroid gland is 2.8 times stronger than that of beta particles emitted by iodine-131. This suggests that astatine is very promising as a therapeutic agent in the treatment of the thyroid gland. A reliable means of removing astatine from the body has also been found. The rhodanide ion blocks the accumulation of astatine in the thyroid gland, forming a strong complex with it. So element number 85 can no longer be called practically useless.
