* Thallium is a member of the main group metals family:
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THALLIUM / Tl / 81
A soft, silvery-white metal that corrodes easily. Two isotopes are
found in nature: Tl<205/81> (70%) and Tl<203/81> (30%). Both are
stable.
atomic weight: 204.3833
abundance: 59th
density: 11.85 gm/cc
melting point: 304 C
boiling point: 1,457 C
valence: <1> 3
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Thallium is not all that rare, but it has few practical applications, with some use in manufacturing highly refractive glasses, photoelectric cells, and infrared detectors. Production is only a few tens of tonnes a year. It is toxic even in fairly small doses.
