Osmium
Osmium is a hard, blue-gray-white transition metal discovered in 1803, and it's the densest naturally occurring element on Earth. Its name comes from the harsh, distinctive smell of one of its compounds, and it's long been valued for extreme hardness and durability.
- Group · Period
- 8 · 6
- At room temp
- solid
- Melts at
- 3306 K
- Density
- 22.57 g/cm³
- Discovered
- 1803
Uses
Because osmium tetroxide vapor is hazardous to handle, pure osmium metal doesn’t see much everyday commercial use. Historically, though, osmium alloyed with other platinum-group metals — a combination sometimes called osmiridium — was valued for its extreme hardness and resistance to wear, and was used for things like fountain pen nib tips, phonograph needles, and the pivots inside precision instruments, applications where a tiny amount of an extraordinarily durable material went a long way. Osmium tetroxide, despite its toxicity, is put to careful, controlled use in biology and materials science laboratories, where it’s used to stain and fix fatty tissue samples so they can be clearly examined under an electron microscope.
History
Osmium was discovered in 1803 by English chemist Smithson Tennant, who found it — along with iridium — in the black residue left behind after dissolving crude platinum ore in acid. Other chemists had noticed this leftover residue before but hadn’t identified what it actually contained. Tennant named the new element osmium after the Greek word for smell, “osme,” inspired by the sharp, distinctive odor of osmium tetroxide, one of the compounds it readily forms.
Fun facts
- Osmium is the densest naturally occurring element, packing more mass into a given volume than any other element found on Earth.
- Its name comes from the Greek word for smell, 'osme,' because osmium tetroxide, one of its compounds, has a strong, harsh odor.
- Osmium tetroxide is used in biology labs to stain and preserve tissue samples for viewing under electron microscopes.
Frequently asked questions
Is osmium really the densest element on Earth?
Yes — osmium and its close neighbor iridium are the two densest naturally occurring elements, with osmium usually measured as very slightly denser. A block of osmium the size of a sugar cube weighs noticeably more than a similarly sized block of lead, even though it doesn't feel dramatically different to the eye.
Why is osmium named after a smell?
When English chemist Smithson Tennant discovered osmium in 1803, he noticed that one of its compounds, osmium tetroxide, had a sharp, unpleasant odor. He named the new element osmium after the Greek word "osme," meaning smell, based on that distinctive and rather harsh-smelling compound.
What is osmium actually used for today?
Pure osmium is rarely used on its own because osmium tetroxide vapor is hazardous, but osmium alloyed with other platinum-group metals has historically been prized for extreme hardness and wear resistance, once used in things like fountain pen nib tips and instrument pivots. Osmium tetroxide itself is carefully used in laboratories as a staining and fixing agent for biological tissue examined under electron microscopes.
Compounds
3 notable compounds containing Os
- OsO2oxide
Osmium dioxide
A black, chemically inert solid with a metallic-like electrical conductivity, formed when osmium sits in its intermediate +4 oxidation state.
Used for: Laboratory intermediate in osmium refining and research chemistry
- OsO4oxide
Osmium tetroxide
A pale yellow, volatile solid with a sharp odor and notoriously toxic vapor, famous for reacting readily with carbon-carbon double bonds.
Used for: Staining agent for lipids in electron microscopy and reagent for alkene dihydroxylation
- OsCl3halide
Osmium(III) chloride
A dark brown to black, water-insoluble solid commonly used as the starting point for making other osmium compounds and complexes.
Used for: Laboratory precursor for osmium coordination chemistry and catalysts
Isotopes
43 known isotopes
Swipe to see all columns →
| Isotope | Natural abundance | Half-life | Decay mode | Mass excess | Binding energy / nucleon | Decay width |
|---|---|---|---|---|---|---|
| Os-184 | 0.02% | 5.6E13 Y | Double beta-plus decay, Alpha decay | -44,252.57 keV | 7,988.68 keV | 2.58 × 10-37 eV |
| Os-186 | 1.59% | 2.0E+15 Y | Alpha decay (100%) | -43,000.03 keV | 7,982.83 keV | 7.23 × 10-39 eV |
| Os-187 stable | 1.96% | Stable | — | -41,219.02 keV | 7,973.78 keV | — |
| Os-188 stable | 13.24% | Stable | — | -41,137.3 keV | 7,973.87 keV | — |
| Os-189 stable | 16.15% | Stable | — | -38,986.8 keV | 7,963 keV | — |
| Os-190 stable | 26.26% | Stable | — | -38,707.83 keV | 7,962.1 keV | — |
| Os-192 stable | 40.78% | Stable | — | -35,882.3 keV | 7,948.53 keV | — |
Show all 43 isotopes
| Os-161 | — | 0.64 ms | Alpha decay (100%) | -10,196 keV | 7,765 keV | 7.13 × 10-13 eV |
| Os-162 | — | 2.1 ms | Alpha decay (99%) | -14,500 keV | 7,794 keV | 2.17 × 10-13 eV |
| Os-163 | — | 5.5 ms | Alpha decay (100%), Electron capture / beta-plus decay | -16,336 keV | 7,807 keV | 8.30 × 10-14 eV |
| Os-164 | — | 21 ms | Alpha decay (96%), Electron capture / beta-plus decay (4%) | -20,424.72 keV | 7,833.31 keV | 2.17 × 10-14 eV |
| Os-165 | — | 71 ms | Alpha decay (90%), Electron capture / beta-plus decay (10%) | -21,747 keV | 7,843 keV | 6.43 × 10-15 eV |
| Os-166 | — | 213 ms | Alpha decay (72%), Electron capture / beta-plus decay (28%) | -25,431.53 keV | 7,866.34 keV | 2.14 × 10-15 eV |
| Os-167 | — | 0.81 s | Alpha decay (57%), Electron capture / beta-plus decay (43%) | -26,498.86 keV | 7,873.96 keV | 5.63 × 10-16 eV |
| Os-168 | — | 2.1 s | Electron capture / beta-plus decay (57%), Alpha decay (43%) | -29,995 keV | 7,895.94 keV | 2.17 × 10-16 eV |
| Os-169 | — | 3.43 s | Electron capture / beta-plus decay (86.3%), Alpha decay (13.7%) | -30,722.98 keV | 7,901.29 keV | 1.33 × 10-16 eV |
| Os-170 | — | 7.37 s | Electron capture / beta-plus decay (90.5%), Alpha decay (9.5%) | -33,925.69 keV | 7,921.13 keV | 6.19 × 10-17 eV |
| Os-171 | — | 8.3 s | Electron capture / beta-plus decay (98.2%), Alpha decay (1.8%) | -34,297.24 keV | 7,924.18 keV | 5.50 × 10-17 eV |
| Os-172 | — | 19.2 s | Electron capture / beta-plus decay (99.8%), Alpha decay (0.2%) | -37,243.64 keV | 7,942.16 keV | 2.38 × 10-17 eV |
| Os-173 | — | 22.4 s | Electron capture / beta-plus decay (99.6%), Alpha decay (0.4%) | -37,438.25 keV | 7,944.03 keV | 2.04 × 10-17 eV |
| Os-174 | — | 44 s | Electron capture (100%), Alpha decay (0.02%) | -39,995.38 keV | 7,959.46 keV | 1.04 × 10-17 eV |
| Os-175 | — | 1.4 m | Electron capture / beta-plus decay (100%) | -40,105.36 keV | 7,960.73 keV | 5.43 × 10-18 eV |
| Os-176 | — | 3.6 m | Electron capture / beta-plus decay (100%) | -42,131.18 keV | 7,972.87 keV | 2.11 × 10-18 eV |
| Os-177 | — | 3.0 m | Electron capture / beta-plus decay (100%) | -41,956.45 keV | 7,972.44 keV | 2.53 × 10-18 eV |
| Os-178 | — | 5.0 m | Electron capture / beta-plus decay (100%), Alpha decay (0%) | -43,544.24 keV | 7,981.91 keV | 1.52 × 10-18 eV |
| Os-179 | — | 6.5 m | Electron capture / beta-plus decay (100%) | -43,020.14 keV | 7,979.48 keV | 1.17 × 10-18 eV |
| Os-180 | — | 21.5 m | Electron capture / beta-plus decay (100%) | -44,356.2 keV | 7,987.42 keV | 3.54 × 10-19 eV |
| Os-181 | — | 105 m | Electron capture / beta-plus decay (100%) | -43,549.97 keV | 7,983.43 keV | 7.24 × 10-20 eV |
| Os-182 | — | 21.84 h | Electron capture (100%) | -44,609.11 keV | 7,989.73 keV | 5.80 × 10-21 eV |
| Os-183 | — | 13.0 h | Electron capture / beta-plus decay (100%) | -43,663.76 keV | 7,985.01 keV | 9.75 × 10-21 eV |
| Os-185 | — | 93.6 d | Electron capture (100%) | -42,805.91 keV | 7,981.3 keV | 5.64 × 10-23 eV |
| Os-191 | — | 15.4 d | Beta-minus decay (100%) | -36,395.24 keV | 7,950.57 keV | 3.43 × 10-22 eV |
| Os-193 | — | 29.830 h | Beta-minus decay (100%) | -33,394.4 keV | 7,936.27 keV | 4.25 × 10-21 eV |
| Os-194 | — | 6.0 Y | Beta-minus decay (100%) | -32,435.18 keV | 7,932.02 keV | 2.41 × 10-24 eV |
| Os-195 | — | 6.5 m | Beta-minus decay | -29,511.6 keV | 7,917.74 keV | 1.17 × 10-18 eV |
| Os-196 | — | 34.9 m | Beta-minus decay (100%) | -28,277.12 keV | 7,912.23 keV | 2.18 × 10-19 eV |
| Os-197 | — | 2.8 m | Beta-minus decay (100%) | -25,080 keV | 7,897 keV | 2.72 × 10-18 eV |
| Os-198 | — | — | Beta-minus decay (100%) | -23,600 keV | 7,890 keV | — |
| Os-199 | — | 5 s | Beta-minus decay (100%) | -20,270 keV | 7,874 keV | 9.12 × 10-17 eV |
| Os-200 | — | 6 s | Beta-minus decay (100%) | -18,550 keV | 7,867 keV | 7.60 × 10-17 eV |
| Os-201 | — | — | Beta-minus decay (100%) | -14,840 keV | 7,849 keV | — |
| Os-202 | — | 160 ns | Beta-minus decay | -12,530 keV | 7,839 keV | 2.85 × 10-9 eV |
| Os-203 | — | — | Beta-minus decay (100%), Beta-minus, neutron emission | -7,270 keV | 7,814 keV | — |