Name: thallium
Symbol: Tl
Atomic number: 81
Atomic weight: 204.3833 (2)
Group in periodic table: 13
Group name:
Period in periodic table: 6
Block in periodic table: p-block
CAS registry ID: 7440-28-0
When freshly exposed to air, thallium exhibits a metallic lustre, but soon develops a bluish-grey tinge, resembling lead in appearance. A heavy oxide builds up on thallium if left in air, and in the presence of water the hydroxide is formed. The metal is very soft and malleable. It can be cut with a knife.