Osmium (Os)

Osmium is a hard, brittle, bluish-white transition metal in the platinum group; it is the densest naturally occurring element.

Core Principles & Analysis

• Smithson Tennant discovered osmium in 1803 in the acid-insoluble residue of platinum ore, naming it from the Greek for smell after its pungent oxide.
• At 22.59 grams per cubic centimeter it is the densest naturally occurring element.
• Osmium alloys tip fountain pen nibs and instrument pivots, and osmium tetroxide stains specimens for electron microscopy and reveals fingerprints.

Specifications & Metrics

• NUM: 76
• SYMBOL: Os
• CATEGORY: Transition Metal
• ATOMIC MASS: 190.2 u
• ELECTRONEGATIVITY: 2.2 Pauling
• ATOMIC RADIUS: 216 pm
• IONIZATION ENERGY: 8.7 eV
• ELECTRON AFFINITY: 1.1 eV
• MELTING POINT: 3306 K
• BOILING POINT: 5285 K
• DENSITY: 22.57 g/cm³
• ELECTRON CONFIGURATION: [Xe]6s2 4f14 5d6
• OXIDATION STATES: +4, +3
• STANDARD STATE: Solid
• GROUP BLOCK: Transition metal
• YEAR DISCOVERED: 1803