Osmium
Osmium is a very dense platinum-group metal; its volatile tetroxide compound is highly toxic.
Osmium packs a remarkable amount of mass into a small volume.
Explore Osmium's atom- Atomic number
- 76
- Standard atomic weight
- 190.23(3)
- Family
- Transition metal
- Period
- 6
- Group
- 8
- Standard state
- Solid
In everyday life
Osmium has niche uses in hard alloys and chemical research.
Something to remember
Osmium is among the densest elements under ordinary conditions.
Meet its electrons
[Xe] 6s2 4f14 5d6
Published neutral-atom ground-state configuration; excited atoms and ions can differ.
Electrons per shell: 2 · 8 · 18 · 32 · 14 · 2.
The playground shows an illustrative shell model. Real electrons are described by quantum orbitals, rather than tiny planets traveling along fixed paths.
A connection to explore
Osmium and iridium form very hard alloys for specialised wear-resistant applications.
Meet Iridium (Ir)Properties and conditions
- Standard atomic weight
- 190.23(3)CIAAW 2024 standard atomic weight (dimensionless). Parentheses give uncertainty in the last quoted digits. Source flags: g.CIAAW standard atomic weights ↗ · Retrieved 2026-10-15
- Standard state
- SolidPubChem classification, including explicit predictions where stated. Reference temperature and pressure are not supplied in the table.PubChem periodic table ↗ · Retrieved 2026-10-15
- First ionisation energy
- 8.7 eVEnergy to remove the first electron from an isolated neutral gas-phase atom. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electronegativity
- 2.2 Pauling scaleA dimensionless relative measure; values depend on the chosen scale. Uncertainty is not supplied.PubChem periodic table ↗ · Retrieved 2026-10-15
- Melting point
- 3306 KPubChem reported value. Pressure, allotrope and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Boiling point
- 5285 KPubChem reported value. Pressure and measurement uncertainty are not specified in the table; consult the cited source.PubChem periodic table ↗ · Retrieved 2026-10-15
- Density
- 22.57 g/cm³PubChem reported value. Temperature, pressure, allotrope and measurement uncertainty are not specified in the table; gas densities are especially condition-dependent.PubChem periodic table ↗ · Retrieved 2026-10-15
- Oxidation states
- +4, +3Selected PubChem oxidation states; formal electron bookkeeping, not a list of stable free-ion charges or every possible compound.PubChem periodic table ↗ · Retrieved 2026-10-15
- Discovery
- 1803PubChem discovery attribution. Ancient knowledge and competing priority claims cannot always be represented by a single year.PubChem periodic table ↗ · Retrieved 2026-10-15
- Atomic radius
- 216 pmPubChem tabulated radius. Radius definitions depend on bonding and convention; measurement definition and uncertainty are not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
- Electron affinity
- 1.1 eVPubChem reported gas-phase electron affinity. Sign conventions and electronic states matter; uncertainty is not supplied in this table.PubChem periodic table ↗ · Retrieved 2026-10-15
Isotopes, abundance and decay
Isotopes share a proton count but have different neutron counts. This selection includes naturally tabulated compositions and a reference isotope for other elements. It is not a list of every known isotope.
Explore 7 isotopes of Os
| Isotope | Relative atomic mass | Natural fraction | Half-life | Decay |
|---|---|---|---|---|
| Os-184 | 183.9524885(14) | 0.0002(1) | 11.2 Ty (uncertainty 2.3) | ;A ?;2β+ ? |
| Os-186 | 185.9538350(16) | 0.0159(3) | 2.0 Py (uncertainty 1.1) | ;α=100 |
| Os-187 | 186.9557474(16) | 0.0196(2) | No decay observed | ; A ? |
| Os-188 | 187.9558352(16) | 0.1324(8) | No decay observed | ;A ? |
| Os-189 | 188.9581442(17) | 0.1615(5) | No decay observed | ; A ? |
| Os-190 | 189.9584437(17) | 0.2626(2) | No decay observed | ;A ? |
| Os-192 | 191.9614770(29) | 0.4078(19) | No decay observed | ;2β− ?;A ? |
Fractions use NIST’s terrestrial isotopic compositions, which can vary by sample. Parentheses denote uncertainty in the last digits. Half-lives and decay branches use NUBASE2020; # marks estimates, >/< mark limits. “No decay observed” follows that evaluation and does not prove permanent stability. Decay branch intensities are percentages; SF means spontaneous fission, EC electron capture, IT an isomeric transition.
Follow the science
Use these original references to explore the data and context. Atomic weights can vary with isotope composition; values for elements without stable isotopes may describe a representative isotope rather than a standard atomic weight.