Osmium
Element 76 · Transition Metal
Osmium is a hard, bluish-white metal with a remarkable density of 22.59 g/cm³ — the highest of any naturally occurring element. It is brittle, has a high melting point, and forms the +8 oxide, osmium tetroxide, in which it reaches its maximum oxidation state.
Its hardness suits fountain pen tips and instrument pivots that must never wear down, and osmium tetroxide — intensely toxic, used only by specialists — stains biological samples for electron microscopy and develops fingerprints.
Key facts
| Atomic number | 76 |
|---|---|
| Atomic weight | 190.23 |
| Category | Transition Metal |
| Group / Period | 8 / 6 |
| Block | d |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d6 |
| Common oxidation states | +4, +8 |
| State at STP | Solid |
| Electronegativity | 2.20 |
| Density | 22.59 g/cm³ |
| Melting point | 3033 °C |
| Boiling point | 5012 °C |
Occurrence
Osmium is one of the rarest stable elements, found in platinum ores and nickel deposits, usually alloyed with iridium as osmiridium.
Applications
Fountain pen tips and instrument pivots
Electrical contacts
Fingerprint detection (osmium tetroxide)
Electron microscopy staining
Common compounds
- osmium tetroxide
- osmium dioxide
Osmium tetroxide has a pungent smell — the element's name comes from the Greek osme, meaning ‘smell’. The compound is highly toxic and used only by specialists.
Data source: IUPAC standard atomic weights 2021