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Osmium (Os)

Osmium is a chemical element of the periodic table with chemical symbol Os and atomic number 76 with an atomic weight of 190.233 u and is classed as transition metal and is part of group 8 (iron group). Osmium is solid at room temperature.

Osmium in the periodic table

Atomic number76
Group8 (Iron group)
ClassificationTransition Metal
AppearanceSilvery, blue cast
Color SlateGray
Number of protons76 p+
Number of neutrons114 n0
Number of electrons76 e-
From Wikipedia, the free encyclopediaOsmium (from Greek osme (ὀσμή) meaning "smell") is a chemical element with 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 a density of 22.59 g/cm3.

Physical properties

Phase at STPSolid
Density22.59 g/cm3
Atomic weight190.233 u

Thermal properties

Melting point3306 K
3032.85 °C
5491.13 °F
Boiling point5285 K
5011.85 °C
9053.33 °F
Heat of vaporization627.6 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)2.2
Electron affinity103.99 kJ/mol
Oxidation states−4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8
(a mildly acidic oxide)
Ionization energies
  1. 840 kJ/mol
  2. 1600 kJ/mol

Electron configuration for osmium

Electron configuration
Shorthand configuration
[Xe] 4f14 5d6 6s2
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d6 6s2
Electron configuration chart
Electrons per shell2, 8, 18, 32, 14, 2
Valence electrons 2
Valency electrons 2,3,4
Bohr model
OsmiumElectron shell for Osmium, created by Injosoft ABOs
Figure: Shell diagram of Osmium (Os) atom.
Orbital Diagram

The history of Osmium

Discovery and first isolationSmithson Tennant (1803)
Named bySmithson Tennant
Discovery of osmium
Osmium was discovered in 1803 by Smithson Tennant and William Hyde Wollaston in London, England. The discovery of osmium is intertwined with that of platinum and the other metals of the platinum group. Platinum reached Europe as platina ("small silver"), first encountered in the late 17th century in silver mines around the Chocó Department, in Colombia. The discovery that this metal was not an alloy, but a distinct new element, was published in 1748. Chemists who studied platinum dissolved it in aqua regia (a mixture of hydrochloric and nitric acids) to create soluble salts. They always observed a small amount of a dark, insoluble residue. Joseph Louis Proust thought that the residue was graphite. Victor Collet-Descotils, Antoine François, comte de Fourcroy, and Louis Nicolas Vauquelin also observed iridium in the black platinum residue in 1803, but did not obtain enough material for further experiments. In 1803, Smithson Tennant analyzed the insoluble residue and concluded that it must contain a new metal. Vauquelin treated the powder alternately with alkali and acids and obtained a volatile new oxide, which he believed was of this new metal—which he named ptene, from the Greek word πτηνος (ptènos) for winged. However, Tennant, who had the advantage of a much larger amount of residue, continued his research and identified two previously undiscovered elements in the black residue, iridium and osmium. He obtained a yellow solution by reactions with sodium hydroxide at red heat. After acidification he was able to distill the formed OsO4. He named it osmium after Greek osme meaning "a smell", because of the ashy and smoky smell of the volatile osmium tetroxide. Discovery of the new elements was documented in a letter to the Royal Society on June 21, 1804.


List of unique identifiers for Osmium in various chemical registry databases
CAS Number7440-04-2
ChemSpider ID22379
EC number231-114-0
PubChem CID Number23937