Symbol	Os
Atomic number	76
Group	8 (Iron group)
Period	6
Block	d
Classification	Transition Metal

Appearance	Silvery, blue cast
Color	SlateGray

Number of protons	76 p+
Number of neutrons	114 n0
Number of electrons	76 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.

Phase at STP	Solid
Density	22.59 g/cm3
Atomic weight	190.233 u

Melting point	3306 K 3032.85 °C 5491.13 °F
Boiling point	5285 K 5011.85 °C 9053.33 °F
Heat of vaporization	627.6 kJ/mol

Electronegativity (Pauling Scale)	2.2
Electron affinity	103.99 kJ/mol
Oxidation states	−4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8 (a mildly acidic oxide)
Ionization energies	840 kJ/mol 1600 kJ/mol

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	1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d6 6s2
Electrons per shell	2, 8, 18, 32, 14, 2
Valence electrons	2
Valency electrons	2,3,4
Bohr model	Figure: Shell diagram of Osmium (Os) atom.
Orbital Diagram 1s 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 6s

Discovery and first isolation	Smithson Tennant (1803)
Named by	Smithson 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.

CAS Number	7440-04-2
ChemSpider ID	22379
EC number	231-114-0
PubChem CID Number	23937