Astatine properties

All isotopes of element 85, astatine, are intensely radioactive with very short half-lives (p. 795). As a consequence weighable amounts of the element or its compounds cannot be prepared and no bulk properties are known. The chemistry of the element must, of necessity, be studied by tracer techniques on extremely dilute solutions, and this introduces the risk of experimental errors and the consequent possibility of erroneous... 

PROPERTY FLUORINE CHLORINE BROMINE IODINE ASTATINE... 

Astatine is a radioactive element that occurs in nature in uranium and thorium ores, but only to a minute extent. Samples are made by bombarding bismuth with a particles in a cyclotron, which accelerates the particles to a very high speed. Astatine isotopes do not exist long enough for its properties to be studied, but it is thought from spectroscopic measurements to have properties similar to those of iodine. 

The element exists as an intermediate in uranium and thorium minerals through their decay. There is no stable isotope. The longest-living isotope has a half-life of 8.3 hours. In the crust of the Earth, the total steady-state mass is estimated at a few tens of grams. Thus astatine is the rarest element (record ). A few atoms of this relative of iodine can be found in all uranium ore. It exhibits certain metallic properties. 

Astatine is located just below iodine, which suggests that it should have some of the same chemical properties as iodine, even though it also acts more hke a metal or semimetal than does iodine. It is a fairly heavy element with an odd atomic number, which assisted chemists in learning more about this extremely rare element. The 41 isotopes are man-made in atomic reactors, and most exist for fractions of a second. The elements melting point is about 302°C, its boiling point is approximately 337°C, and its density is about 7g/cm. ... 

Astatine is the heaviest and densest of the elements in group 17 (VIIA). It is difficult to determine the chemical and physical properties and characteristics of astatine because it is present in such small quantities that exist for extremely short periods of time. Many of its characteristics are inferred through experiments rather than by direct observations. 

In water solution astatine resembles iodine in some of its chemical and physical properties. Both are powerful oxidizing agents. 

Astatine, generally speaking, is a difficult isotope to study from a chemical viewpoint because no stable isotopes exist. Although the study of the chemical properties of astatine began over 40 years ago (44), the element s precise behavior is still in doubt. The chemical similarity between astatine and its nearest halogenic neighbor, iodine, is not always obvious. In many cases the astatine tracer has not... 

Astatine, regardless of its electronic state vide infra), appears to possess many physiobiochemical properties similar to those of its nearest homolog, iodine 34, 57, 60, 119, 176). However, astatine also exhibits a proclivity to accumulate in macrophage-laden tissue, such as lungs, liver, and spleen 37, 60, 119) this has been attributed to its amphoteric character. 

Astatine-211 (ti/2 = 7.21 hours) possesses many of the desired physical (Fig. 5), chemical, and radiobiological properties thought pertinent to its possible application in cancer therapy (26,33,34,36,40). Astatine-211 decays along two branches (1) by direct a-particle decay (41.94 + 0.50% 5.87 MeV) to (tj/j = 38 years), which decays by electron... 

Aminosulfur trifluorides, 19 192 syntheses and properties of, 14 347-348 Aminotroponeimines, 32 29 5-Aminouracil, astatination, 31 75 Aminousulfanuryl fluoride ions, 19 226,... 

Astatine, 6 207-223, 31 43-88 as astatate ion, 6 219-220 as astatide ion, properties of, 6 217-218 biochemical compounds of, 6 222 biochemical fate, 31 78 biological behavior, 6 222 31 77-78 biomedical applications, 31 79-83 therapeutic studies, 31 80-81 chemical properties of, 6 216 diatomic, 31 50 distallation, 31 47-48 elementary, 6 218-219 embryotoxicity, 31 78 extraction techniques, 31 47 identification, 31 49 in intermediate oxidation state, 6 219 iodide, 6 218-219 isotopes, 31 43-49 decay, 31 44 half-lives, 31 44 decay and half-lives of, 6 210 experimental methods for, 6 213-216 production and measurement of, 6 209-216... 

Chloroxytrifluoromethane, 26 137-139 reactions, 26 140-143 addition to alkenes, 26 145-146 oxidative addition, 26 141-145 vibrational spectra, 26 139 Chloryl cation, 18 356-359 internal force constants of, 18 359 molecular structure of, 18 358, 359 properties of, 18 357, 358 synthesis of, 18 357, 358 vibrational spectra of, 18 358, 359 Chloryl compounds, reactions of, 5 61 Chloryl fluoride, 18 347-356 chemical properties of, 18 353-356 fluoride complexes of, 5 59 molecular structure of, 18 349-352 physical properties of, 18 352, 353 preparation, 5 55-57 and reactions, 27 176 properties of, 5 48 reactions, 5 58-61, 18 356 synthesis of, 18 347-349 thermal decomposition of, 18 354, 355 vapor pressures, 5 57, 18 353 vibrational spectra of, 18 349-352 Chloryl ion, 9 277 Cholegobin, 46 529 Cholesterol, astatination, 31 7 Cholorofluorphosphine, 13 378-380 h CHjPRj complexes, osmium, 37 274 Chromatium, HiPIP sequence, 38 249 Chromatium vinosum HiPIP, 38 108, 133 Fe4S4 + core, 33 60 Chromato complexes, osmium, 37 287... 

Astatine has properties very similar to those of iodine, but has a more metallic character. The oxidation of astatide to astatine occurs at a potential ca. 0.4 V less positive compared to that for the oxidation of iodine. Fundamental information about the redox chemistry of astatine is available in an earlier review [158] and standard data collections [14]. A summary of the approximate standard potentials and known redox states is given in Scheme 8. 

Only limited information about the electrochemical properties of astatine is available. The formation of a singly positively charged cation, At+, in aqueous and other solvent environments has been observed. A study in a nitric acid environment investigated the adsorption into ion exchange materials of this cation [206]. In a similar study in aqueous perchloric acid, the mobility of At+ was found to change with pH and the presence of a strongly water bound species, At(H20)2", with a pA of ca. 1.5 was proposed [207]. 

In 1940 D. R. Corson, K. R. Mackenzie, and E. Segre at the University of California bombarded bismuth with alpha particles (26, 27). Preliminary tracer studies indicated that they had obtained element 85, which appeared to possess metallic properties. The pressure of war work prevented a continuation of these studies at the time. After the war, the investigators resumed their work, and in 1947 proposed the name astatine, symbol At, for their element. The name comes from the Greek word for unstable, since this element is the only halogen without stable isotopes (28). The longest lived isotope is At210 with a half-life of 8.3 hours and a very high activity. 

Tracer studies of the chemical properties showed that astatine was soluble in organic solvents, could be reduced to the —1 state, and had at least two positive oxidation states. These studies were made on solutions of 10-11 to KL15 molar astatine (29). The similarity between astatine and iodine was found to be less close than that between technetium and rhenium or that between promethium and the other rare earths (30). 

Elements bordering the staircase (boron, silicon, germanium, arsenic, antimony, tellurium, polonium, and astatine) are called metalloids because they have properties between those of metals and nonmetals. Chemists debate the membership of certain elements (especially polonium and astatine) within the metalloids, but the list here reflects an inclusive view. You can find these elements in Groups lllA, IVA, VA, VIA, and VllA. 

Given that astatine (At) is similar in properties to chlorine (Cl), and that gallium (Ga) is similar to aluminum (Al), write the formulas for the following compounds. 

This review will attempt to deal with the chemistry of the halogens appropriate to those compounds considered as coordination compounds. It will not include reference to astatine, which is covered by the general reviews listed above and for which little chemistry is known at all, and almost none as a coordinated ligand. Since the chemistry of the halides of individual elements is treated in the chapters for those elements, this section will be concerned with an overview of the general properties of the group. 

Semimetals Seven of the nine elements adjacent to the zigzag boundary between metals and nonmetals—boron, silicon, germanium, arsenic, antimony, tellurium, and astatine—are known as semimetals, or metalloids, because their properties are intermediate between those of their metallic and nonmetallic neighbors. Though most are silvery in appearance and all are solid at room temperature, semimetals are brittle rather than malleable and tend to be poor conductors of heat and electricity. Silicon, for example, is a widely used semiconductor, a substance whose electrical conductivity is intermediate between that of a metal and an insulator. 

The quantity of astatine produced in this manner was extremely small but nevertheless sufficient to permit study of some of the chemical properties of this element and unequivocally establish its identity. 

Astatine is an exception to many of these properties because it is an artificial metalloid. 

The decade that has elapsed since the previous survey on the organic chemistry of astatine was published in this series1 has seen a considerable increase of knowledge. The most important results that have been achieved are those concerning the preparation and identification of astatine-labelled organic compounds utilizable for biomedical purposes and those from studying their chemical and biochemical properties. Much less has been... 

---