76. Osmium
Name: Osmium
Symbol: Os
Atomic Number: 76
Atomic Mass: 190.23 amu
Melting Point: 3045.0 °C (3318.15 °K, 5513.0 °F)
Boiling Point: 5027.0 °C (5300.15 °K, 9080.6 °F)
Number of Protons/Electrons: 76
Number of Neutrons: 114
Classification: Transition Metal
Crystal Structure: Hexagonal
Density(293 K): 22.4 g/cm3
Color: silvery
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.
Osmium (Greek osme meaning "a smell") was discovered in 1803 by Smithson Tennant in London, England along with iridium in the residue of dissolving platinum in aqua regia.
Osmium tetroxide is highly toxic. Airborne concentrations of osmium as low as 10-7 g/m3 can cause lung congestion, skin or eye damage.
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