Osmium (Os)

Silvery, blue cast

Osmium is the densest naturally occurring element at 22.59 g/cm³, heavier than gold or platinum, and with [Xe] 4f¹⁴ 5d⁶ 6s², osmium's extreme density results from its contracted atomic radius and strong metallic bonding. OsO₄ is used as a stain in electron microscopy and in fingerprint detection.

Key metrics

Density22.59g/cm³

Melting point3,306K

Boiling point5,285K

Electronegativity2.2Pauling

Discovery

1803discovered

Discovered by: Smithson Tennant
Reactivity profile: Forms toxic oxide
Reactivity: Low
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Xe]}\; \textcolor{#a855f7}{4_{f}^{14}}\; \textcolor{#22c55e}{5_{d}^{6}}\; \textcolor{#ef4444}{6_{s}^{2}}

[Xe] 4f14 5d6 6s2

Wave function

\Psi_{\text{Os}} \approx \frac{1}{\sqrt{76!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{76}(\mathbf{r}_{76}) \right|

Probability density $|\Psi|^2$ across the Os valence shell.

Crystal structure

Hexagonal Close-Packed

Lattice constantsa 1.00 · b 1.00 · c 1.63

Cell anglesα 90° · β 90° · γ 120°

Coordination number12

Atoms per cell2

Atomic packing factor0.74

Physical properties

Atomic radius: 135 pm
Ionization energy: 840 kJ/mol
Electron affinity: 106 kJ/mol
Crystal structure: Hexagonal close-packed (hcp)

Oxidation states

+2+3+4+6+8

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

3306 K5285 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

426.1nmOs IViolet70%

442.0nmOs I (blue)Violet100%

558.6nmOs I (green)Green40%

Dominant line 442.0 nmRange 426–559 nmTransitions 3