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Astatine                               

Standard Sate: solid at 298k

Color: Metallic                                                                                                                        

The longest-lived isotope, ²¹⁰At, has a half-life of only 8.3 hours. There are about 20 isotopes known, all of which are radioactive. Astatine is a halogen and possibly accumulates in the thyroid like iodine.

(AT), radioactive chemical element, heaviest member of the halogen
elements, or Group VIIa of the periodic table. Astatine, which has no
stable isotopes, was first synthetically produced (1940) at the
University of California by Dale R. Corson, K.R. MacKenzie, and
Emilio Segr�, who bombarded bismuth with accelerated alpha
particles (helium nuclei) to yield astatine and neutrons. Naturally
occurring astatine isotopes have subsequently been found in minute
amounts in the three natural radioactive decay series in which they
occur by minor branching (astatine-218 in the uranium series,
astatine-216 in the thorium series, and astatine-215 and
astatine-219 in the actinium series). About 20 isotopes are known;
astatine-210, with a half-life of 8.3 hours, is the longest lived.

Because of the short half-lives of astatine isotopes, only very small
quantities have been available for study. By the use of astatine-210
and astatine-211 and the tracer methods of radiochemistry, some of
the chemical properties of the element have been established. It
generally resembles iodine (thus, like iodine, it concentrates in the
thyroid gland of higher animals). It is somewhat soluble in water and
much more soluble in benzene and carbon tetrachloride. Astatine can
be reduced to the astatide ion, At-, and has been oxidized to positive
oxidation states that appear to be +1 (AtO-) and +5 (AtO-3). atomic
number 85 stablest isotope 210 oxidation states -1, +1, +3(?), +5,
+7(?) electronic config. 2-8-18-32-18-7 or (Xe)4f 145d106s26p5

"astatine" Encyclop�dia Britannica Online.

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