Osmium (Os)
Transition metal
Osmium is the densest naturally occurring element — a litre of it would weigh more than 22 kg. This brittle, blue-tinged metal hardens alloys for fountain-pen tips, instrument pivots and electrical contacts.
Position on the periodic table
Atomic properties
| Atomic number | 76 |
|---|---|
| Atomic mass | 190.233 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d6 |
| Noble gas shorthand | [Xe] 4f14 5d6 6s2 |
| Electrons per shell | 2, 8, 18, 32, 14, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +4, +3, +8 |
| Electronegativity (Pauling) | 2.2 |
| Covalent radius (approx.) | 144 pm |
| First ionization energy | 840 kJ/mol |
| Electron affinity | 104 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 22.59 g/cm³ |
| Melting point | 3032.8 °C (3306 K) |
| Boiling point | 5011.9 °C (5285 K) |
| Appearance | silvery, blue cast |
| Radioactive | No |
| Origin | Occurs naturally |
Electron configuration of osmium
Osmium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d6, usually shortened to [Xe] 4f14 5d6 6s2. Its electrons occupy 6 shells (2, 8, 18, 32, 14, 2), placing it in period 6 of the d-block. Explore it interactively in the electron configuration calculator.
Uses of osmium
- Ultra-hard alloy tips for fountain pens and instruments
- Electrical contacts
- Staining agent in electron microscopy (OsO₄)
Biological role: None known.
Occurrence: Extremely rare; recovered from platinum ores.
Common compounds of osmium
OsO4
Osmium tetroxide
History and discovery
Discovered: 1803 — Smithson Tennant. Name origin: From Greek osme, “smell”, after the sharp odour of its volatile oxide.
Smithson Tennant discovered osmium (and iridium) in 1803 in the black residue left when platinum dissolves in aqua regia.
Safety notes
The metal is safe, but osmium tetroxide vapour is severely toxic to eyes and lungs — a strict fume-hood chemical.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Osmium
1. What is the chemical symbol of Osmium?
2. What is the atomic number of Osmium?
3. Which category does Osmium belong to?
4. What is the state of Osmium at room temperature?
5. Which period of the periodic table is Osmium in?
Osmium FAQs
What is the atomic number of osmium?
Osmium's atomic number is 76 — every osmium atom has 76 protons in its nucleus.
What is the symbol for osmium?
Os. From Greek osme, “smell”, after the sharp odour of its volatile oxide.
Is osmium a metal, nonmetal, or metalloid?
Osmium is classified as a transition metal.
What state is osmium at room temperature?
At about 25 °C, osmium is a solid. It melts at 3032.8 °C.
What is osmium used for?
Key uses include: ultra-hard alloy tips for fountain pens and instruments; electrical contacts; staining agent in electron microscopy (oso₄).
Related elements
Keep working with this element
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