Periodic Table

Osmium

Transition Metal

Quick Facts about Osmium

Re
  • solid- state of matter at room temperature
  • Stable- has at least one stable isotope
  • +4, +3- common oxidation states in compounds
  • HEX- crystal structure, atomic arrangement in solid form
Ir

Osmium (Os) is element 76 on the periodic table. Atomic mass of Os: 190.2300 u. Os is in period 6, group 8. Melting point of Os: 3306.00 K.Density of Os: 22.59 g/cm³.

Why Osmium Matters

Osmium in everyday life and industry

Industry Uses

Writing instrumentsFountain pen tips use osmium alloys for extreme hardness and wear resistance
Precision instrumentsElectrical contacts and instrument pivots use osmium alloys
ScientificOsO4 stains biological samples for electron microscopy
ForensicsOsO4 vapor develops latent fingerprints

In Your Body

✗ Not essential

Osmium has no known biological role.

Safety: Osmium tetroxide is extremely toxic and damages eyes and lungs. The metal itself is relatively safe but oxidizes to toxic OsO4. Osmium tetroxide vapor can cause blindness.

Discovery of Osmium

Discovered by Smithson Tenant in England, 1804

Name origin: Greek: osmê (odor).

History & Events

1803
Named from Greek 'osme' meaning smell, for its pungent oxide
1803
Discovered by Smithson Tennant in 1803 along with iridium
1803
The densest naturally occurring element
1803
Found in platinum ore residues

About Osmium

The densest naturally occurring element at 22.59 g/cm3, slightly edging out iridium. Seven natural isotopes exist; Os-186 is primordial radioactive (α, t1/2=2×1015 years). Named from Greek 'osme' (smell) for the pungent, toxic OsO4 oxide that forms when the metal oxidizes. Used in ultra-hard alloys with platinum and iridium for fountain pen tips and instrument pivots.

Atomic Properties of Os

Atomic Number of Os
76
Atomic Mass of Os
190.2300 u
Electron Configuration
[Xe] 4f14 5d6 6s2
Electronegativity
2.20
Block
d-block
Group
8
Period
6

Physical Properties of Os

Phase (STP)
solid
Melting Point of Os
3306.00 K
Boiling Point of Os
5285.00 K
Density of Os
22.5900 g/cm3

Thermal Properties

Heat of Fusion
31.70 kJ/mol
Heat of Vaporization
738.00 kJ/mol
Specific Heat
0.13 J/g·K
Molar Heat Capacity
24.70 J/mol·K

Atomic Radii

Calculated
130 pm
Covalent
129 pm
Van der Waals
216 pm
Metallic
126 pm

Common Misconceptions

Wrong:Osmium is the heaviest element.
Correct:Many elements have higher atomic masses, but osmium is the densest—packing the most mass per unit volume at 22.59 g/cm3.
Wrong:Osmium metal has a distinctive smell.
Correct:The metal itself is odorless. The pungent smell comes from toxic OsO4 that forms when osmium oxidizes in air—hence the name from Greek 'osme' (smell).
Wrong:Osmium is commonly used in jewelry like other platinum group metals.
Correct:Despite being precious and extremely hard, osmium's tendency to form toxic OsO4 makes it impractical for jewelry. It's used industrially in alloys for pen tips and instruments.

Isotopes of Osmium

Osmium has 6 naturally occurring isotopes, plus 1 notable radioactive isotope.

IsotopeAtomic Mass (u)AbundanceHalf-LifeDecay Mode
18476Os (Os-184)Osmium-184 isotope183.95248850.0200%——
18676Os (Os-186)Osmium-186 isotope185.9538351.590%2.0×10¹⁵ yearsα
18776Os (Os-187)Osmium-187 isotope186.95574741.960%——
18876Os (Os-188)Osmium-188 isotope187.955835213.24%——
18976Os (Os-189)Osmium-189 isotope188.958144216.15%——
19076Os (Os-190)Osmium-190 isotope189.958443726.26%——
19276Os (Os-192)Osmium-192 isotope191.96147740.78%——

Data source: NIH PubChem (aggregated from IUPAC, NIST)

Isotope Applications

Isotopes of Osmium have important real-world applications in science and industry.

Geochronology & Dating

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]. Kirk et al. [519] 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]. 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.

Abundance

Earth's Crust
1.50 μg/kg

Uses

Used to tip gold pen points, instrument pivots, to make electric light filaments. Used for high temp. alloys and pressure bearings. Very hard and resists corrosion better than any other.

Sources

Obtained from the same ores as platinum.

Geochemistry

Goldschmidt
siderophile
Geochemical Class
noble metal

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