Osmium

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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, though bulk metal is less prone to forming the oxide than the powder. A lower oxide, osmium dioxide, is known. It forms coordination complexes easily.

Physical properties

Osmium is a hard, brittle, white-bluish transition metal and usually is found in traces in platinum ores. It is the densest non-radioactive element known, with a density of 22.6 g/cm3 (22.59 g/cm3 according to most sources), slightly denser than iridium. It's almost twice as dense as lead. It melts at 3033 ºC, 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 and sometimes from eBay.

Projects

  • Osmium tetroxide synthesis (Dangerous! Toxic!)
  • Organoosmium compounds
  • Element collection

Handling

Safety

Osmium metal poses very little toxicity as it does not react with most reagents. Osmium powder, however, will slowly oxidize in air to form osmium tetroxide, which is toxic and a powerful oxidant. Osmium powder is also pyrophoric. The bulk metal, however, is safe to keep in air.

Storage

Bulk osmium does not require any special storage. Osmium powder should be kept in closed containers, in a well ventilated area, preferable under a gas other than air (such as carbon dioxide).

Disposal

Due to osmium's high price, it's best to try and recycle it as much possible.

References

Relevant Sciencemadness threads