Name: osmium
Symbol: Os
Atomic number: 76
Atomic weight: 190.23 (3) g
Group in periodic table: 8
Group name: Precious metal
Period in periodic table: 6
Block in periodic table: d-block
CAS registry ID: 7440-04-2
Osmium metal is lustrous, bluish white, extremely hard, and brittle even at high temperatures. It has the highest melting point and lowest vapour pressure of the platinum group. The metal is very difficult to fabricate, but the powder can be sintered in a hydrogen atmosphere at a temperature of 2000°C. The solid metal is not affected by air at room temperature, but the powdered or spongy metal slowly gives off osmium tetroxide, which is a powerful oxidising agent and has a strong smell. The tetroxide is highly toxic, and boils at 130°C (760 mm). Concentrations in air as low as 10-7 g m-3 can cause lung congestion, skin damage, or eye damage.