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Osmium - Os

General Information


Osmium was discovered by S. Tennant in 1803 in London.


Osmium is lustrous, bluish-white, extremely hard and has a pungent smell.


Osmium occurs in the free state and in the mineral osmiridium, but commercial recovery is from the wastes of nickel refining.


Osmium is almost entirely used to produce very hard alloys for fountain pen tips, instrument pivots, needles and electrical contacts.

Biological Role

Osmium has no known biological role, but is very toxic, and can cause lung, skin and eye damage.

General Information

Osmium metal is unaffected by air, water and acids, but dissolves in molten alkalis. The powdered metal slowly gives off osmium (VIII) oxide, the source of its pungent odor.


Extra pure Osmium of 190.2 mol. wt. is available from Sigma-Aldrich for $140.35 per gram.

  More Physical Information    
  Melting Point/K   3327
  Boiling Point/K   5300
  Density/kg m-3   22590 (293K)
  Ground State Electron Configuration   [Xe]4f145d66s2
  Electron Affinity(M-M-)/kJ mol-1   139

  Key Isotopes          
  nuclide 184Os 185Os 186Os 187Os 188Os
  atomic mass 183.9   185.9 186.9 187.9
  natural abundance 0.02% 0% 1.58% 1.6% 13.3%
  half-life stable 9.6 days stable stable stable
  nuclide 189Os 190Os 191Os 192Os  
  atomic mass 188.9 189.9   191.9  
  natural abundance 16.1% 26.4% 0% 41%
  half-life stable stable 15 days stable  


Other Information  
Enthalpy of Fusion/kJ mol-1 29.3
Enthalpy of Vaporization/kJ mol-1 738
Oxidation States  
main OsIV
others Os-II, OsO, OsI, OsII, OsIII,
  Ionisation Energies/kJ mol-1
  M - M+ 840
  M+ - M2+ 1600
  M2+ - M3+ 2400
  M3+ - M4+ 3900
  M4+ - M5+ 5200
  M5+ - M6+ 6600
  M6+ - M7+ 8100
  M7+ - M8+ 9500
  M8+ - M9+  
  M9+ - M10+



It would not normally be necessary to make a sample of osmium in the laboratory as the metal is available, at a price, commercially. The industrial extraction of osmium is complex as the metal occurs in ores mixed with other metals such as ruthenium, rhodium, palladium, silver, platinum, and gold. Sometimes extraction of the precious metals such as iridium, rhodium, platinum and palladium is the main focus of a particular industrial operation while in other cases it is a byproduct. The extraction is complex because of the other metals present and only worthwhile since osmium is useful as a specialist metal and is the basis of some catalysts in industry.

Preliminary treatment of the ore or base metal byproduct is required to remove silver, gold, palladium, and platinum. The residue is melted with sodium bisulphate (NaHSO4) and the resulting mixture extracted with water to give a solution containing rhodium sulphate, Rh2(SO4)3. The insoluble residue contains the osmium. The residue is melted with Na2O2 and extracted into water to extract the ruthenium and osmium salts (including [RuO4]2- and [OsO4(OH)2]2-). The residue contains iridium oxide, IrO2. Reaction of the salt with chlorine gas gives the volatile oxides RuO4 and OsO4. The osmium oxide is dissolved by treatment with alcoholic sodium hydroxide to form Na2[OsO2(OH)4], and the osmium precipiated out as pure OsCl2O2(NH3)4 by treatment with NH4Cl. Evaporation to dryness and burning under hydrogen gas gives pure osmium.



The popular death-metal band OSMIUM

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[Image]Did you know....?

That Shania Twain, the members of 'N Sync and Sam Donaldson have all said that Osmium is their favorite chemical element!