Osmium (from Ancient Greek ὀσμή (osmḗ) 'smell') is a chemical element; it has symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mostly in platinum ores. Osmium is the densest naturally occurring element. When experimentally measured using X-ray crystallography, it has a density of 22.59 g/cm3.[10] Manufacturers use its alloys with platinum, iridium, and other platinum-group metals to make fountain pen nib tipping, electrical contacts, and in other applications that require extreme durability and hardness.
Quick Facts Pronunciation, Appearance ...
Osmium, 76Os |
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Pronunciation | (OZ-mee-əm) |
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Appearance | silvery, blue cast |
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Atomic number (Z) | 76 |
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Group | group 8 |
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Period | period 6 |
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Block | d-block |
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Electron configuration | [Xe] 4f14 5d6 6s2 |
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Electrons per shell | 2, 8, 18, 32, 14, 2 |
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Phase at STP | solid |
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Melting point | 3306 K (3033 °C, 5491 °F)[3] |
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Boiling point | 5281 K (5008 °C, 9046 °F)[4] |
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Density (at 20° C) | 22.587 g/cm3[5] |
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when liquid (at m.p.) | 20 g/cm3 |
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Heat of fusion | 31 kJ/mol |
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Heat of vaporization | 378 kJ/mol |
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Molar heat capacity | 24.7 J/(mol·K) |
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Vapor pressure
P (Pa) |
1 |
10 |
100 |
1 k |
10 k |
100 k |
at T (K) |
3160 |
3423 |
3751 |
4148 |
4638 |
5256 |
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Oxidation states | −4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8 (a mildly acidic oxide) |
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Electronegativity | Pauling scale: 2.2 |
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Ionization energies | - 1st: 840 kJ/mol
- 2nd: 1600 kJ/mol
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Atomic radius | empirical: 135 pm |
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Covalent radius | 144±4 pm |
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Spectral lines of osmium |
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Natural occurrence | primordial |
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Crystal structure | hexagonal close-packed (hcp) (hP2) |
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Lattice constants | a = 273.42 pm c = 431.99 pm (at 20 °C)[6] |
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Thermal expansion | 4.99×10−6/K (at 20 °C)[lower-alpha 1] |
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Thermal conductivity | 87.6 W/(m⋅K) |
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Electrical resistivity | 81.2 nΩ⋅m (at 0 °C) |
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Magnetic ordering | paramagnetic |
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Molar magnetic susceptibility | 11×10−6 cm3/mol |
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Shear modulus | 222 GPa |
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Bulk modulus | 462 GPa |
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Speed of sound thin rod | 4940 m/s (at 20 °C) |
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Poisson ratio | 0.25 |
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Mohs hardness | 7.0 |
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Vickers hardness | 4137 MPa |
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Brinell hardness | 3920 MPa |
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CAS Number | 7440-04-2 |
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Discovery and first isolation | Smithson Tennant (1803) |
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Category: Osmium | references |
Close
Osmium is among the rarest elements in the Earth's crust, making up only 50 parts per trillion (ppt).[12][13]