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Astatine is a chemical element; it has symbol At and atomic number 85. ... [35] Many values have been predicted for the melting and boiling points of astatine, ...
The Gmelin rare earths handbook lists 1522 °C and 1550 °C as two melting points given in the literature, the most recent reference [Handbook on the chemistry and physics of rare earths, vol.12 (1989)] is given with 1529 °C.
Analytical Chemistry of Technetium, Promethium, Astatine, and Francium. Translated by R. Kondor. Ann Arbor–Humphrey Science Publishers. p. 269. ... Melting points ...
It has a melting point of 450 °C and a boiling point of 988 °C. Tellurium has a polyatomic (CN 2) hexagonal crystalline structure. It is a semiconductor with a band gap of 0.32 to 0.38 eV. Tellurium has a moderate ionisation energy (869.3 kJ/mol), high electron affinity (190 kJ/mol), and moderate electronegativity (2.1).
Astatine-212 and astatine-216 are expected to decay either way. The most stable isotope of astatine is astatine-210, which has a half-life of about 8.1 hours. This isotope's primary decay mode is positron emission to the relatively long-lived alpha emitter, polonium-210. In total, only five isotopes of astatine have half-lives exceeding one ...
It is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal; it probably has a higher melting point than iodine. Chemically, several anionic species of astatine are known and most of its compounds resemble those of iodine.
Astatine is a radioactive element that has never been seen; a visible quantity would immediately be vaporised due to its intense radioactivity. [172] It may be possible to prevent this with sufficient cooling. [173] Astatine is commonly regarded as a nonmetal, [174] less commonly as a metalloid [175] and occasionally as a metal.
Astatine chloride Astatine bromide Astatine iodide. Iodine monofluoride (IF) is unstable and decomposes at 0 °C, disproportionating into elemental iodine and iodine pentafluoride. Bromine monochloride (BrCl) is a yellow-brown gas with a boiling point of 5 °C.