Thallium
Chemical element
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Thallium is a chemical element; it has symbol Tl and atomic number 81. It is a gray post-transition metal that is not found free in nature. When isolated, thallium resembles tin, but discolors when exposed to air. Wikipedia
Symbol: Tl
Atomic number: 81
Atomic mass: 204.3833 u
Discovered: 1861
Melting point: 578.9°F (303.8°C)
Discoverer: William Crookes
Boiling point: 2,683°F (1,473°C)