O

Osmium

IUPAC: Osmium

Os Elements CAS 7440-04-2
Quick Reference
Formula / NotationOs
CAS Number7440-04-2
Molecular Weight190.23
Melting Point3033.0
Boiling Point5012.0
Density22.59
SolubilityInsoluble in water
AppearanceHard, lustrous, blue-grey metal
Also Known AsOs, osmium metal
CategoryElements

What is Osmium?

Osmium is a hard, lustrous, blue-grey transition metal, atomic number 76. The densest naturally occurring element (22.59 g/cm3). Osmium tetroxide (OsO4) is extremely toxic and volatile. Most osmium is used as hard alloy with platinum group metals.

Formula & Notation

Os

IUPAC Name: Osmium

Other Names / Synonyms: Os, osmium metal

Properties & Characteristics

Atomic number: 76. Atomic mass: 190.23 g/mol. Period 6, Group 8. Melting point: 3033 C. Boiling point: 5012 C. Density: 22.59 g/cm3 (densest element). Electronegativity: 2.20. Oxidation states: -2 to +8. Seven stable isotopes.

Physical Data

PropertyValue
Melting Point3033.0
Boiling Point5012.0
Density22.59
Molecular Weight190.23
SolubilityInsoluble in water
AppearanceHard, lustrous, blue-grey metal

Uses & Applications

Platinum-osmium alloys for fountain pen tips, pivots, electrical contacts (extreme hardness). Osmium tetroxide (OsO4) staining agent in electron microscopy. OsO4 as oxidant in dihydroxylation of alkenes. Historical compass needles and pivot bearings.

Safety Information

Osmium tetroxide (OsO4): highly toxic - IDLH 0.001 ppm, causes severe eye damage (corneal damage) and lung damage even at trace levels. Osmium metal slowly oxidises to OsO4 in air. Osmium dust: toxic fumes risk. Work with OsO4 only in fume hood with eye protection.

Always consult the SDS/MSDS before handling any chemical. This information is for educational purposes only.

Key Facts

Term Osmium
Formula Os
CAS Number 7440-04-2
Molecular Weight 190.23
Category Elements
Synonyms Os, osmium metal

Frequently Asked Questions

Osmium is a hard, lustrous, blue-grey transition metal, atomic number 76. The densest naturally occurring element (22.59 g/cm3). Osmium tetroxide (OsO4) is extremely toxic and volatile. Most osmium is used as hard alloy with platinum group metals.

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