|
|
Oxidation & Electrons | Appearance & Characteristics Reactions | Compounds | Radius | Conductivity Abundance & Isotopes 
Left: Electron microscopy image of osmium catalyst clusters containing nominally 5 atoms of osmium each, dispersed on a magnesium oxide support material. (Photo: ORNL) Right: Osmium Bead (Photo: Tomihahndorf) |
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 |
| Discovered: 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. | |
States
| State (s, l, g): solid | |
| Melting point: 3303 K (3030 oC) | Boiling point: 5285 K (5012 oC) |
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 |
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 |
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. |
|
|
Characteristics: 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 OC. See data source.) Osmium has the highest melting point and the lowest vapor pressure of the platinum group (ruthenium, rhodium, palladium, iridium, and platinum). |
|
|
Uses: 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. |
|
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 |
Compounds
| Oxide(s): OsO2, OsO4 | Chloride(s): OsCl3, OsCl4, OsCl5 |
| Hydride(s): none |
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 |
Conductivity
| Thermal conductivity: 87.6 W m-1 K-1 | Electrical conductivity: 12.3 x 10-6 S m-1 |
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 | |
| Source: 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. | |
| Isotopes: 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%. | |
