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Osmium,  76Os
Osmium crystals.jpg
Osmium
Pronunciation/ˈɒzmiəm/ (OZ-mee-əm)
Appearancesilvery, blue cast
Standard atomic weight Ar, std(Os)190.23(3)
Osmium in the periodic table
Hydrogen
Helium
Lithium Beryllium
Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium
Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium
Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium

Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Ru

Os

Hs
rheniumosmiumiridium
Atomic number (Z)76
Groupgroup 8
Periodperiod 6
Blockd-block
Element category  Transition metal
Electron configuration[Xe] 4f14 5d6 6s2
Electrons per shell
2, 8, 18, 32, 14, 2
Physical properties
Phase at STPsolid
Melting point3306 K ​(3033 °C, ​5491 °F)
Boiling point5285 K ​(5012 °C, ​9054 °F)
Density (near r.t.)22.59 g/cm3
when liquid (at m.p.)20 g/cm3
Heat of fusion31 kJ/mol
Heat of vaporization378 kJ/mol
Molar heat capacity24.7 J/(mol·K)
Vapor pressure
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 3160 3423 3751 4148 4638 5256
Atomic properties
Oxidation states−4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8 (a mildly acidic oxide)
ElectronegativityPauling scale: 2.2
Ionization energies
  • 1st: 840 kJ/mol
  • 2nd: 1600 kJ/mol

Atomic radiusempirical: 135 pm
Covalent radius144±4 pm
Color lines in a spectral range
Spectral lines of osmium
Other properties
Natural occurrenceprimordial
Crystal structurehexagonal close-packed (hcp)
Hexagonal close packed crystal structure for osmium
Speed of sound thin rod4940 m/s (at 20 °C)
Thermal expansion5.1 µm/(m·K) (at 25 °C)
Thermal conductivity87.6 W/(m·K)
Electrical resistivity81.2 nΩ·m (at 0 °C)
Magnetic orderingparamagnetic
Magnetic susceptibility11·10−6 cm3/mol
Shear modulus222 GPa
Bulk modulus462 GPa
Poisson ratio0.25
Mohs hardness7.0
Vickers hardness300 MPa
Brinell hardness293 MPa
CAS Number7440-04-2
History
Discovery and first isolationSmithson Tennant (1803)
Main isotopes of osmium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
184Os 0.02% stable
185Os syn 93.6 d ε 185Re
186Os 1.59% 2.0×1015 y α 182W
187Os 1.96% stable
188Os 13.24% stable
189Os 16.15% stable
190Os 26.26% stable
191Os syn 15.4 d β 191Ir
192Os 40.78% stable
193Os syn 30.11 d β 193Ir
194Os syn 6 y β 194Ir

Osmium (from Greek ὀσμή osme, "smell") is a chemical element with the 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, with an experimentally measured (using x-ray crystallography) density of 22.59 g/cm3. 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. The element's abundance in the Earth's crust is among the rarest.

Characteristics