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Osmium General

Name:Osmium Symbol:Os
Type:Transition Metal Atomic weight:190.2
Density @ 293 K: 22.61 g/cm3 Atomic volume:8.49 cm3/mol

Osmium was discovered in 1803 by Smithson Tennant in the residue left when crude platinum was dissolved by aqua regia (a mixture of hydrochloric acid and nitric acid). Smithson Tennant also discovered iridium at the same time. Osmium's name comes from the Greek word 'osme' meaning a smell associated with toxic osmium tetroxide (OsO4), released by the powdered metal in air.

Osmium States

State (s, l, g): solid
Melting point:3303 K (3030 °C) Boiling point:5285 K (5012 °C)

Osmium Energies

Specific heat capacity:0.13 J g-1 K-1 Heat of atomization:789 kJ mol-1
Heat of fusion:31.80 kJ mol-1 Heat of vaporization :627.6 kJ mol-1
1st ionization energy:840 kJ mol-1 2nd ionization energy:1600 kJ mol-1
3rd ionization energy:kJ mol-1 Electron affinity:104 kJ mol-1

Osmium Oxidation & Electrons

Shells: 2,8,18,32,14,2 Electron configuration:[Xe] 4f14 5d6 6s2
Minimum oxidation number:-2 Maximum oxidation number:8
Min. common oxidation no.:0 Max. common oxidation no.:4
Electronegativity (Pauling Scale): 2.2 Polarizability volume: 8.5 Å3

Osmium Appearance & Characteristics

Structure:hcp: hexagonal close pkd Color:bluish-white
Hardness:7.0 mohs
Harmful effects:

Powdered osmium in air forms the pungent, highly toxic osmium tetroxide (OsO4) which can cause lung, skin and eye damage.


Osmium is a rare, lustrous, very hard, brittle, bluish-white metal. It is the densest of all the elements. (Although osmium's density is very similar to iridiums, osmium's is slightly higher - both measured and calculated. Calculated: Osmium 22.587 ± 0.009 g/cm3   &   Iridium: 22.562 ± 0.009 g/cm3 at 20 °C. See data source.) Osmium has the highest melting point and the lowest vapor pressure of the platinum group (ruthenium, rhodium, palladium, iridium, and platinum).


Osmium is principally used alloyed with other metals in the platinum group to produce very hard alloys. An alloy of 90% platinum and 10% osmium is used in surgical implants such as pacemakers and replacement heart valves. Osmium tetroxide is used in microscopy as a stain for fatty tissue and in fingerprint detection.

Osmium Reactions

Reaction with air:mild, ⇒ OsO4 Reaction with 6 M HCl:none
Reaction with 15 M HNO3:mild, ⇒ OsO2 Reaction with 6 M NaOH:none

Osmium Compounds

Oxide(s):OsO2, OsO4 Chloride(s):OsCl3, OsCl4, OsCl5

Osmium Radius

Atomic radius:135 pm Ionic radius (1+ ion):pm
Ionic radius (2+ ion):pm Ionic radius (3+ ion):pm
Ionic radius (2- ion):pm Ionic radius (1- ion):pm

Osmium Conductivity

Thermal conductivity:87.6 W m-1 K-1 Electrical conductivity:12.3 x 106 S m-1

Osmium Abundance & Isotopes

Abundance earth's crust: 1.5 parts per billion by weight, 0.2 parts per billion by moles
Abundance solar system: 2 parts per billion by weight, 20 parts per trillion by moles
Cost, pure:$7700 per 100g
Cost, bulk:$ per 100g

Osmium is found in platinum ores and in the mineral osmiridium (an alloy of osmium and iridium). Commercially, osmium is recovered as a by-product of nickel refining.


Osmium has 34 isotopes whose half-lives are known, with mass numbers from 162 to 196. Of these, five are stable: 187Os, 188Os, 189Os, 190Os and 192Os. Naturally the most common isotope is 192Os, with an abundance of 40.1%.

Osmium Other



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