Astatine

    Astatine is the heaviest member of group 17 and is known only in the form of radioactive isotopes, all of which have short half-lives. The longest lived isotope is ²¹⁰At (t_1/2= 8.1 h). Several isotopes are present naturally as transient products of the decay of uranium and thorium minerals; ²¹⁸At is formed from the β-decay of ²¹⁸Po, but the path competes with decay to ²¹⁴Pb.  

     Other isotopes are artificially prepared, e.g. ²¹¹At (an α emitter) from the nuclear reaction ²⁰⁹₈₃Bi(α,2n)²¹¹₈₅At, and may be separated by vacuum distillation. In general, At is chemically similar to iodine. Tracer studies (which are the only sources of information about the element) show that At₂ is less volatile than I₂, is soluble in organic solvents, and is reduced by SO₂ to At^- which can be coprecipitated with AgI or TlI. Hypochlorite, [ClO]^-, or peroxodisulfate, [S₂O₈]^2-, oxidizes astatine to an anion that is carried by [IO₃]^- (e.g. coprecipitation with AgIO₃) and is therefore probably [AtO₃]^-. Less powerful oxidizing agents such as Br₂ also oxidize astatine, probably to [AtO]^- or [AtO₂]^-.

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