A nuclear isomer may also be called a "meta-state", meaning the system has more internal energy than the "ground state" (the state with the lowest possible internal energy), making the former likely to decay into the latter. The reactions involved have been typically tested with dilute solutions of astatine mixed with larger amounts of iodine. Astatine-211 has potential for targeted alpha-particle therapy, since it decays either via emission of an alpha particle (to bismuth-207),[134] or via electron capture (to an extremely short-lived nuclide, polonium-211, which undergoes further alpha decay), very quickly reaching its stable granddaughter lead-207. In early 1947, Nature published the discoverers' suggestions; a letter from Corson, MacKenzie, and Segrè suggested the name "astatine"[93] coming from the Greek astatos (αστατος) meaning "unstable", because of its propensity for radioactive decay, with the ending "-ine", found in the names of the four previously discovered halogens. Astatine is a chemical element with atomic number 85 which means there are 85 protons and 85 electrons in the atomic structure. [61] As mentioned, there are grounds for instead referring to this compound as astatine hydride. The astatine electronic configuration is given by [Xe] 4f145d106s26p5. Astatine-211 has a significantly higher energy than the previous isotope, because it has a nucleus with 126 neutrons, and 126 is a magic number corresponding to a filled neutron shell. Unlike iodine, astatine also shows a tendency to be taken up by the lungs and spleen, possibly because of in-body oxidation of At– to At+. This element exhibits similar chemical properties that of the element iodine. The marked reduction for At was predicted as being due to spin–orbit interactions.[41]. [97], Corson and his colleagues classified astatine as a metal on the basis of its analytical chemistry. [133] It must be used quickly as it decays with a half-life of 7.2 hours; this is long enough to permit multistep labeling strategies. Therefore, astatine-211 is very much less stable toward alpha decay than astatine-210. Unlike iodine, astatine shows a tendency to dehalogenate from molecular carriers such as these, particularly at sp3 carbon sites[p] (less so from sp2 sites). [43][44] It forms complexes with EDTA, a metal chelating agent,[45] and is capable of acting as a metal in antibody radiolabeling; in some respects astatine in the +1 state is akin to silver in the same state. At + e – → At – – ∆H = Affinity = 270.1 kJ/mol. Even though only one bismuth isotope is used (bismuth-209), the reaction may occur in three possible ways, producing astatine-209, astatine-210, or astatine-211. [8][j] The two following isotopes release even more energy, with astatine-213 releasing the most energy. Characteristic Electronic Configuration of Halogens: All halogens contain seven electrons in their outermost shell. Despite this shortcoming, the Allred-Rochow scale has achieved a relatively high degree of acceptance. In total, only five isotopes have half-lives exceeding one hour (astatine-207 to -211). [57][72], In 1869, when Dmitri Mendeleev published his periodic table, the space under iodine was empty; after Niels Bohr established the physical basis of the classification of chemical elements, it was suggested that the fifth halogen belonged there. This half-vaporization period grows to 16 hours if it is instead put on a gold or a platinum surface; this may be caused by poorly understood interactions between astatine and these. All other shells are completely filled. [8], Astatine has 24 known nuclear isomers, which are nuclei with one or more nucleons (protons or neutrons) in an excited state. [98] Subsequent investigators reported iodine-like,[99][100] cationic,[101][102] or amphoteric behavior. Electron Configuration Chart for All Elements in the Periodic Table. Astatine is a halogen and it is quite possible that it accumulates in the human thyroid just like iodine. The number may be dropped if there is only one well-established meta state, such as astatine-216m. In this regard, what's the end of the electron configuration for zirconium? [122][138][q], Animal studies show that astatine, similarly to iodine – although to a lesser extent, perhaps because of its slightly more metallic nature[109]  – is preferentially (and dangerously) concentrated in the thyroid gland. Astatine's most stable isotope, astatine-210, has a half-life of 8.1 hours. [46] If administered in the form of a radiocolloid it tends to concentrate in the liver. [l] The total amount of astatine in the Earth's crust (quoted mass 2.36 × 1025 grams)[108] is estimated by some to be less than one gram at any given time. [136], P Durbin, Human Radiation Studies: Remembering the Early Years, 1995, Several obstacles have been encountered in the development of astatine-based radiopharmaceuticals for cancer treatment. Bismuth oxide can be used instead; this is forcibly fused with a copper plate. 2. The reason for this was that at the time, an element created synthetically in "invisible quantities" that had not yet been discovered in nature was not seen as a completely valid one; in addition, chemists were reluctant to recognize radioactive isotopes as legitimately as stable ones. Metallic bismuth may be used as a target material. As per the astatine definition, it is the 85th element in the periodic table that has a symbol At. It is mainly formed by the decaying of the thorium and uranium elements. Karlik and Bernert were unsuccessful in reproducing his experiments, and subsequently attributed Minder's results to contamination of his radon stream (radon-222 is the parent isotope of polonium-218). Following this first step, the acid can be distilled away to leave behind a white residue that contains both bismuth and the desired astatine product. Considerations. [89] He had also been involved in an earlier false claim as to the discovery of element 87 (francium) and this is thought to have caused other researchers to downplay his work. [139] Early research suggested that injection of astatine into female rodents caused morphological changes in breast tissue;[140] this conclusion remained controversial for many years. Chlorine monofluoride, chlorine, and tetrafluorosilane were formed. [106] Lighter astatine isotopes have quite high energies of alpha decay, which become lower as the nuclei become heavier. The astatine atomic number is 85. [83], The first claimed discovery of eka-iodine was made by Fred Allison and his associates at the Alabama Polytechnic Institute (now Auburn University) in 1931. [88], In 1936, the team of Romanian physicist Horia Hulubei and French physicist Yvette Cauchois claimed to have discovered element 85 via X-ray analysis. Several methods are available, "but they generally follow one of two approaches—dry distillation or [wet] acid treatment of the target followed by solvent extraction." There may be more than one isomer for each isotope. Astatine atoms have 85 electrons and the shell structure is 2.8.18.32.18.7. the atomic number of astatine is 85. Higher temperatures of up to around 850 °C may increase the yield, at the risk of bismuth contamination from concurrent volatilization. Due to the small amounts produced and its short half-life, there are currently no uses for astatine outside of basic scientific research. 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