Name thallium
Symbol Tl
Atomic Weight 204.3833
Atomic Number 81
CAS ID 7440-28-0
Group Number 13
Group Name (none)
Period Number 6
Origin of Name Greek, thallos = "green twig."
Year Discovered 1861
Discovery Credits Discovered by W. Crookes at London, UK; isolated in 1862 by C. A. Lamy at Paris, France.
Class Metallic
Color Silvery White
Standard State Solid at 77 F & 298 K
Description Soft, silvery-gray metal. Tarnishes readily in moist air and with steam reacts to form TlOH. Attacked by acids, rapidly by HNO3. Little used because of its toxicity, but still employed in special glasses.

Diagnostic tests: 
Thallium and its salts are quite volatile when heated with the blowpipe and impart an intense green color to the flame.

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