Osmium
transition metalProperties
| Property | Value |
|---|---|
| Atomic Mass | 190.23 amu |
| Category | transition metal |
| Group | 8 |
| Period | 6 |
| Electron Configuration | [Xe] 4f14 5d6 6s2 |
| Electronegativity | 2.2 (Pauling) |
| Oxidation States | 8, 6, 4, 3, 2, -2 |
| Melting Point | 3306 K (3032.8 °C) |
| Boiling Point | 5285 K (5011.9 °C) |
| Density | 22.59 g/cm³ |
| Discovered By | Smithson Tennant (1803) |
About Osmium
Osmium is the densest stable element you can put on a balance — 22.59 g/cm³, a hair denser than iridium depending on which crystallographic measurement you trust. That density comes from lanthanide contraction packing the 5d shell tight, not from anything exotic about the nucleus. The element was pulled out of platinum-ore residues by Smithson Tennant in 1803 along with iridium, and it took its name from the Greek osme — smell — because tetroxide formation in air gives off a pungent, eye-watering vapor that you remember the first time you encounter it. OsO₄ is the workhorse compound in synthetic chemistry: it dihydroxylates alkenes via the [3+2] cycloaddition Sharpless turned into an asymmetric reaction, sharing the 2001 Nobel for it. Electron microscopists rely on the same volatility and electron density to fix and stain biological tissue. The bulk metal is hard but brittle and almost never machined; you see it mostly as the hard tip in osmiridium fountain-pen nibs.
Fun Fact
Osmium is so dense that if you could fill a standard milk jug with osmium, it would weigh about 85 kilograms (187 pounds) — roughly the weight of an adult person.
Common Uses
- OsO₄ as the standard dihydroxylation reagent for alkenes (Upjohn, Sharpless)
- Heavy-metal fixative and electron-dense stain in transmission electron microscopy
- Osmiridium tips on fountain-pen nibs and precision instrument pivots
- Catalyst in selected ammonia-synthesis and hydrogenation studies
- Latent-fingerprint development via OsO₄ vapor in forensic labs