Osmium
Osmium is the chemical element with symbol Os and atomic number 76.
Properties
Chemical properties
Osmium forms compounds with oxidation state from -2 to 8. It is slightly attacked by aqua regia, and by fuming nitric acid, and it is attacked by molten hydroxides. It forms the toxic osmium tetroxide (OsO4), the most common compound with +8 oxidation state, in contact with air. A lower oxide, osmium dioxide, is known. It forms coordination complexes easily.
Physical properties
Osmium is a hard, brittle, and bluish transition metal and usually is found in traces in platinum ores. It is the densest element known, with a density of 22.6 g/cm3, slightly denser than iridium. It's almost twice as dense as lead. It melts at 3033 Cº, which makes it unfeasible for the amateur chemist to cast.
Availability
It is one of the rarest elements so it is quite expensive. It can be bought online from Metallium.
Safety
Osmium tetroxide is toxic and a powerful oxidant, and it slowly forms through oxidation of fine osmium powder. Osmium powder is also pyrophoric. The bulk metal, however, is safe to keep in air.
