Osmium (Os)
transition-metalSolid
Standard Atomic Weight
190.23 uElectron configuration
[Xe] 6s2 4f14 5d6Melting point
3032.85 °CBoiling point
5011.85 °CDensity
2.25872e+4 kg/m³Oxidation states
−4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8Electronegativity (Pauling)
2.2Ionization energy (1st)
8.43823 eVDiscovery year
1803Atomic radius
130 pmDetails
Osmium is a very dense, hard, blue-white platinum-group metal. It is chemically noble in compact metallic form but is notable for forming volatile and highly toxic osmium tetroxide. Natural osmium occurs with other platinum-group elements in ultramafic ores and placer deposits, chiefly as alloys and sulfide-bearing mineral assemblages. Its rarity, difficult fabrication, and toxicity of some compounds limit its use despite unusual physical and chemical properties.
The metal is lustrous, bluish white, extremely hard, and brittle even at high temperatures. It has the highest melting point and the lowest vapor pressure of the platinum group. The metal is very difficult to fabricate, but the powdered or spongy metal slowly gives off osmium tetroxide, which as a powerful oxidizing agent and has a strong smell. The tetroxide is highly toxic, and boils at 130°C.
Density measurements show osmium to be a little more dense than iridium, and osmium is often cited as the heavier element. However, calculations of the density from the space lattice, which may be more reliable than these measurements, give a density of 22.65 for iridium compared to 22.61 for osmium. According to IUPAC, because of this apparent contradiction, no decision has been made as to which is heavier.
The name derives from the Greek osme for "smell" because of the sharp odor of its volatile oxide. Both osmium and iridium were discovered simultaneously in a crude platinum ore by the English chemist Smithson Tennant in 1803.
Osmium and iridium were discovered at the same time by the British chemist Smithson Tennant in 1803. Osmium and iridium were identified in the black residue remaining after dissolving platinum ore with aqua regia, a mixture of 25% nitric acid (HNO3) and 75% hydrochloric acid (HCl). Today, osmium is primarily recovered during the processing of platinum and nickel ores.
Discovered in 1803 by Tennant in the residue left when crude platinum is dissolved by aqua regia.
Pure osmium is a lustrous bluish white to blue-gray metal. It is extremely dense and hard but also brittle, so it is not readily shaped by ordinary metalworking. Finely divided osmium can oxidize slowly in air to form volatile osmium tetroxide.
Osmium metal has had limited historical use in very hard wear-resistant alloys, including early fountain-pen tips, instrument pivots, and electrical contacts, but most such uses have been replaced by other platinum-group alloys or tungsten materials. Osmium tetroxide, OsO₄, remains important in microscopy as a stain and fixative for unsaturated lipids and biological membranes. Osmium compounds are also used as specialized oxidation catalysts and reagents in organic synthesis, generally on small laboratory or fine-chemical scales.
Metallic osmium is hard, brittle and very difficult to make. Powdered osmium is easier to make but emits osmium tetroxide (OsO4) when it is exposed to the air. Unfortunately, osmium tetroxide smells bad and is very poisonous. Because of these problems, osmium is primarily used to make very hard alloys. Osmium alloys can be found in ball point pen tips, fountain pen tips, record player needles, electrical contacts and other devices where frictional wear must be minimized.
The tetroxide has been used to detect fingerprints and to stain fatty tissue for microscope slides. The metal is almost entirely used to produce very hard alloys with other metals of the platinum group for fountain pen tips, instrument pivots, phonograph needles, and electrical contacts.
Isotopes in Earth/Planetary Science
The isotope-amount ratio n(187Os)/n(186Os) in rocks can be transferred to fluids, such as magmas, groundwaters, rivers, and oceans. Variations in the inherited n(187Os)/n(186Os) ratios can provide a useful tracer for fluid sources and migration paths, including different layers of the Earth [301] G. Faure. Principles of Isotope Geology, 2nd Edition. p. 608. Wiley, New York (1986)., [504] A. Schersten. Re-Os, Pt-Os and Hf-W Isotopes and Tracing the Core in Mantle Melts, MantlePlumes.org (2014), Feb. 25; http://www.mantleplumes.org/Os-W.html., [516] A. D. Brandon, R. J. Walker. Earth. Planet. Sci. Lett.3-4 (232), 211 (2005)., [517] M. Sharma, G. J. Wasserburg, A. W. Hofmann, G. J. Chakrapani. Geochim. Cosmochim. Acta63 (23-24), 4005 (1999).. Meteorites and meteorite dust impacting the Earth have different osmium isotopic compositions than terrestrial rocks and sediments. As a result, n(187Os)/n(186Os)-ratio studies provide evidence of continuing extraterrestrial additions to the Earth over geologic time, as well as providing a method for prospecting in the sedimentary record for large meteorite impact events that may have affected life on Earth [518] F. S. Paquay, G. E. Ravizza, T. K. Dalai, B. Peucker-Ehrenbrink. Science320 (5873), 214 (2008)..
Isotopes in Geochronology
Some 187Os is radiogenic as a result of being formed by the beta decay of radioactive 187Re, which has a half-life of 4.16×1010 years. Variations in the isotope-amount ratio n(187Os)/n(186Os) and amount ratio n(187Re)/n(186Os) are used for geochronology; for example, variations in these ratios have been used to determine the ages of the Earth, Moon, and meteorites [301] G. Faure. Principles of Isotope Geology, 2nd Edition. p. 608. Wiley, New York (1986).. Kirk et al. [519] J. Kirk, J. Ruiz, J. Chesley, J. Walshe, G. England. Science297, 1856 (2002). measured rhenium-osmium isotopic abundances in gold and pyrites from conglomerates of the Central Rand Group of South Africa (Fig. IUPAC.76.1), which have produced over 48 000 metric tons of gold and have accounted for 40 percent of the world’s total historic production [520] H. E. Frimmel, W. E. L. Minter. Soc. Econ. Geol. Spec. Publ.9, 17 (2002).. The gold and rounded pyrites from the conglomerates yield an age of ~3.0×109 years. Kirk et al. find that this age is much older than that of the conglomerate, and they conclude that the gold is detrital (material wearing away by weathering or erosion) and was not deposited by later hydrothermal fluids.
Isotopes Used as a Source of Radioactive Isotope(s)
192Os can be used for the production of the medical radioisotope 195mPt via the 192Os (α, n) 195mPt reaction.
Osmium shows a wide range of oxidation states, from negative states in carbonyl complexes to the high +8 state. Osmium tetroxide, OsO₄, is the best-known compound; it is volatile, strongly oxidizing, and formed by oxidation of osmium metal or lower oxides. Osmium dioxide, OsO₂, is a stable dark oxide with rutile-type structure. Halide chemistry includes osmium tetrachloride, OsCl₄, and chloroosmate complexes such as hexachloroosmate(IV), [OsCl₆]²⁻. Organometallic and carbonyl complexes are important in coordination chemistry but are not bulk materials.
See more information at the Osmium compound page.
Compact osmium metal is relatively inert, but powders and sponges are hazardous because they can produce osmium tetroxide, OsO₄, in air. OsO₄ is highly toxic, volatile, and a strong oxidant; it can damage eyes, skin, and respiratory tissue at very low exposure levels. Osmium compounds should be treated as toxic laboratory chemicals. Natural osmium contains stable isotopes and is not a radiological hazard in ordinary material.
Concentrations in air as low as 107 g/m3 can cause lung congestion, skin damage, or eye damage. Exposure to osmium tetroxide should not exceed 0.0016 mg/m3 (8-hour time weighted average - 40-hour work week).
Osmium is a trace element in the crust and is commonly associated with platinum-group minerals in mafic and ultramafic rocks. It is highly particle-reactive in many natural settings and can be transported in detrital grains or bound to sulfides and organic-rich sediments. The rhenium-osmium isotope system is used to date some ores and sedimentary rocks. Environmental releases are normally very small, but soluble or volatile osmium compounds can be locally significant in laboratories and specialized industry.
Osmium is recovered as a minor by-product of platinum and nickel-copper ore processing rather than mined as a primary product. Separation from other platinum-group metals is technically demanding because of similar chemistry and because volatile osmium tetroxide, OsO₄, must be controlled. Demand is small and specialized, centered on laboratory reagents, catalysts, and limited alloy applications. Recycling occurs mainly through recovery of platinum-group metal residues rather than through a large independent osmium market. Substitution is common where hardness, corrosion resistance, or catalytic behavior can be supplied by iridium, ruthenium, platinum alloys, or non-precious materials.
Osmium occurs in iridosule and in platinum-bearing river sands in the Urals, North America, and South America. It is also found in the nickel-bearing ores of Sudbury, Ontario region along with other platinum metals. While the quantity of platinum metals in these ores is very small, the large tonnages of processed nickel ores make commercial recovery possible.
Osmium is a heavy element made mainly by neutron-capture processes in earlier generations of stars, with contributions from both rapid and slow neutron-capture pathways depending on isotope. It is rare in the solar system but enriched with other siderophile platinum-group elements in metallic phases. Its isotopic ratios are useful tracers in meteoritic and planetary differentiation studies.
- Osmium is usually cited as the densest naturally occurring element, very close to iridium.
- The name comes from the Greek word for smell, referring to the sharp odor of osmium tetroxide.
- Osmium tetroxide reacts with carbon-carbon double bonds, which underlies its use in staining lipids.
- Some osmiridium alloys occur naturally as hard metallic grains in placer deposits.
- The isotope ¹⁸⁷Os is the decay product of long-lived ¹⁸⁷Re.
Images
Properties
Physical
- Atomic radius (empirical)
- 130 pm Compare Atomic radius (empirical) of all elements →
- Covalent radius
- 144 pm Compare Covalent radius of all elements →
- Van der Waals radius
- 216 pm Compare Van der Waals radius of all elements →
- Metallic radius
- 126 pm Compare Metallic radius of all elements →
- Density
- 2.25872 × 104 kg/m³ Compare Density of all elements →
- Molar volume
- 0.00843 L/mol
- Phase at STP
- Solid Compare Phase at STP of all elements →
- Melting point
- 3032.85 °C Compare Melting point of all elements →
- Boiling point
- 5011.85 °C Compare Boiling point of all elements →
- Specific heat capacity
- 0.13 J/(g·K) Compare Specific heat capacity of all elements →
- Molar heat capacity
- 24.7 J/(mol·K) Compare Molar heat capacity of all elements →
- Crystal structure
- Hexagonal close-packed Compare Crystal structure of all elements →
Chemical
- Electronegativity (Pauling)
- 2.2 Compare Electronegativity (Pauling) of all elements →
- Electronegativity (Allen)
- 1.65
- Electron affinity
- 1.1 eV
- Ionization energy (1st)
- 8.43823 eV Compare Ionization energy (1st) of all elements →
- Ionization energy (2nd)
- 17.000059 eV Compare Ionization energy (2nd) of all elements →
- Ionization energy (3rd)
- 25.000086 eV Compare Ionization energy (3rd) of all elements →
- Ionization energy (4th)
- 41.000141 eV Compare Ionization energy (4th) of all elements →
- Ionization energy (5th)
- 55.000189 eV Compare Ionization energy (5th) of all elements →
- Oxidation states
- −4, −2, −1, 0, +1, +2, +3, +4, +5, +6, +7, +8 Compare Oxidation states of all elements →
- Valence electrons
- 8 Compare Valence electrons of all elements →
- Electron configuration
- [Xe] 6s2 4f14 5d6
Thermodynamic
- Heat of fusion
- 0.32854848 eV Compare Heat of fusion of all elements →
- Heat of vaporization
- 6.425869 eV Compare Heat of vaporization of all elements →
- Heat of sublimation
- 8.187801 eV
- Heat of atomization
- 8.187801 eV
- Atomization enthalpy
- 8.156708 eV
Nuclear
- Protons
- 76 Compare Protons of all elements →
- Neutrons
- 116 Compare Neutrons of all elements →
- Known isotopes
- 43 Compare Known isotopes of all elements →
- Stable isotopes
- 0 Compare Stable isotopes of all elements →
- Most stable isotope
- Os-192
- Discovery year
- 1803
Abundance
- Abundance (Earth's crust)
- 0.002 mg/kg Compare Abundance (Earth's crust) of all elements →
Crystal Structure
- Lattice constant a
- 274 pm
Electronic Structure
- Electrons per shell
- 2, 8, 18, 32, 14, 2 Compare Electrons per shell of all elements →
Identifiers
- CAS number
- 7440-04-2 Compare CAS number of all elements →
- Term symbol
- 5D4
- InChI
- InChI=1S/Os
- InChI Key
- SYQBFIAQOQZEGI-UHFFFAOYSA-N
Electron Configuration Measured
Os: 4f¹⁴ 5d⁶ 6s²[Xe] 4f¹⁴ 5d⁶ 6s²1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d⁶ 6s²Atomic model
Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.
Schematic atomic model, not to scale.
Atomic Fingerprint
Emission / Absorption Spectrum
Isotope Distribution
No stable isotopes.
| Mass number | Atomic mass (u) | Natural abundance | Half-life |
|---|---|---|---|
| 167 Radioactive | 166.971549 ± 0.000078 | N/A | 839 ms |
| 161 Radioactive | 160.98903 ± 0.00043 | N/A | 640 us |
| 203 Radioactive | 202.992195 ± 0.000429 | N/A | 300 ms |
| 166 Radioactive | 165.972692 ± 0.00002 | N/A | 213 ms |
| 198 Radioactive | 197.97441 ± 0.00021 | N/A | 125 seconds |
Phase / State
Reason: 3007.8 °C below melting point (3032.85 °C)
Schematic, not to scale
Phase transition points
Transition energies
Energy required to melt 1 mol at melting point
Energy required to vaporize 1 mol at boiling point
Energy required to sublime 1 mol at sublimation point
Density
At standard conditions
At standard conditions
Atomic Spectra
Showing 10 of 76. Sorted by ion charge (ascending).
Lines Holdings ?
| Ion | Charge | Total lines | Transition probabilities | Level designations |
|---|---|---|---|---|
| Os I | 0 | 534 | 0 | 0 |
| Os II | +1 | 38 | 0 | 0 |
| Os III | +2 | 1061 | 1061 | 1061 |
Levels Holdings ?
| Ion | Charge | Levels |
|---|---|---|
| Os I | 0 | 274 |
| Os II | +1 | 40 |
| Os III | +2 | 201 |
| Os IV | +3 | 2 |
| Os V | +4 | 2 |
| Os VI | +5 | 2 |
| Os VII | +6 | 2 |
| Os VIII | +7 | 2 |
| Os IX | +8 | 2 |
| Os X | +9 | 2 |
Ionic Radii
| Charge | Coordination | Spin | Radius |
|---|---|---|---|
| +4 | 6 | N/A | 63 pm |
| +5 | 6 | N/A | 57.49999999999999 pm |
| +6 | 5 | N/A | 49 pm |
| +6 | 6 | N/A | 54.50000000000001 pm |
| +7 | 6 | N/A | 52.5 pm |
| +8 | 4 | N/A | 39 pm |
Compounds
Isotopes (5)
| Mass number | Atomic mass (u) | Natural abundance | Half-life | Decay mode | |
|---|---|---|---|---|---|
| 167 Radioactive | 166.971549 ± 0.000078 | N/A | 839 ms | α =51±0.4%β+ ? | |
| 161 Radioactive | 160.98903 ± 0.00043 | N/A | 640 us | α ≈100% | |
| 203 Radioactive | 202.992195 ± 0.000429 | N/A | 300 ms | β- ?β-n ? | |
| 166 Radioactive | 165.972692 ± 0.00002 | N/A | 213 ms | α =83±0.4%β+ =17±0.4% | |
| 198 Radioactive | 197.97441 ± 0.00021 | N/A | 125 seconds | β- =100% |
Extended Properties
Covalent Radii (Extended)
- Covalent radius (Pyykkö)
- 129 pm
- Covalent radius (Pyykkö, double)
- 116 pm
- Covalent radius (Pyykkö, triple)
- 109 pm
Van der Waals Radii
- Batsanov
- 200 pm
- Alvarez
- 248 pm
- UFF
- 312 pm
- MM3
- 235 pm
Atomic & Metallic Radii
- Atomic radius (Rahm)
- 244 pm
- Metallic radius (C12)
- 135 pm
Numbering Scales
- Mendeleev
- 61
- Pettifor
- 62
- Glawe
- 60
Electronegativity Scales
- Ghosh
- 0
- Miedema
- 5
- Gunnarsson–Lundqvist
- 6
- Robles–Bartolotti
- 5
Polarizability & Dispersion
- Dipole polarizability
- 57 a.u.
- Dipole polarizability (unc.)
- 3 a.u.
- C₆ (Gould–Bučko)
- 584 Ha·Bohr6
Miedema Parameters
- Miedema molar volume
- 8.45 cm3/mol
- Miedema electron density
- 6
Supply Risk & Economics
- Production concentration
- 60
- Relative supply risk
- 8
- Reserve distribution
- 95
- Political stability (top producer)
- 44
- Political stability (top reserve)
- 44
Phase Transitions & Allotropes
| Melting point | 3306.15 K |
| Boiling point | 5281.15 K |
Oxidation State Categories
Advanced Reference Data
Screening Constants (14)
| n | Orbital | σ |
|---|---|---|
| 1 | s | 1.4701 |
| 2 | p | 4.4502 |
| 2 | s | 19.8502 |
| 3 | d | 13.5253 |
| 3 | p | 21.7483 |
| 3 | s | 22.5727 |
| 4 | d | 37.142 |
| 4 | f | 38.8472 |
| 4 | p | 34.856 |
| 4 | s | 33.9048 |
Crystal Radii Detail (6)
| Charge | CN | Spin | rcrystal (pm) | Origin |
|---|---|---|---|---|
| 4 | VI | 77 | from r^3 vs V plots, from metallic oxides, | |
| 5 | VI | 71.5 | estimated, | |
| 6 | V | 63 | ||
| 6 | VI | 68.5 | estimated, | |
| 7 | VI | 66.5 | estimated, | |
| 8 | IV | 53 |
Isotope Decay Modes (58)
| Isotope | Mode | Intensity |
|---|---|---|
| 161 | A | 100% |
| 162 | A | 100% |
| 163 | A | 100% |
| 163 | B+ | — |
| 164 | A | 96% |
| 164 | B+ | — |
| 165 | A | 90% |
| 165 | B+ | 10% |
| 166 | A | 83% |
| 166 | B+ | 17% |
X‑ray Scattering Factors (516)
| Energy (eV) | f₁ | f₂ |
|---|---|---|
| 10 | — | 1.88117 |
| 10.1617 | — | 1.93789 |
| 10.3261 | — | 1.99632 |
| 10.4931 | — | 2.05652 |
| 10.6628 | — | 2.13032 |
| 10.8353 | — | 2.20812 |
| 11.0106 | — | 2.28877 |
| 11.1886 | — | 2.37237 |
| 11.3696 | — | 2.45796 |
| 11.5535 | — | 2.53755 |
Additional Data
Estimated Crustal Abundance
The estimated element abundance in the earth's crust.
1.5×10-3 milligrams per kilogram
References (1)
Estimated Oceanic Abundance
The estimated element abundance in the earth's oceans.
Not Applicable
References (1)
Sources
Sources of this element.
Osmium occurs in iridosule and in platinum-bearing river sands in the Urals, North America, and South America. It is also found in the nickel-bearing ores of Sudbury, Ontario region along with other platinum metals. While the quantity of platinum metals in these ores is very small, the large tonnages of processed nickel ores make commercial recovery possible.
References (1)
- [6] Osmium https://periodic.lanl.gov/76.shtml
References
(9)
Data deposited in or computed by PubChem
The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.
Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.
The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.
Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/
The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.
The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database
This section provides all form of data related to element Osmium.
The element property data was retrieved from publications.