Iridium (Ir)

Silvery-white metal

Iridium is the most corrosion-resistant metal known, marking the asteroid that killed the dinosaurs, and with [Xe] 4f¹⁴ 5d⁷ 6s², iridium is insoluble in all single acids and resists attack by aqua regia. The global iridium anomaly at the K-Pg boundary (66 million years ago) confirmed the Chicxulub asteroid impact theory.

Key metrics

Density22.56g/cm³

Melting point2,719K

Boiling point4,701K

Electronegativity2.2Pauling

Discovery

1803discovered

Discovered by: Smithson Tennant
Reactivity profile: Extremely corrosion resistant
Reactivity: Low
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Xe]}\; \textcolor{#a855f7}{4_{f}^{14}}\; \textcolor{#22c55e}{5_{d}^{7}}\; \textcolor{#ef4444}{6_{s}^{2}}

[Xe] 4f14 5d7 6s2

Wave function

\Psi_{\text{Ir}} \approx \frac{1}{\sqrt{77!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{77}(\mathbf{r}_{77}) \right|

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

Crystal structure

Face-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number12

Atoms per cell4

Atomic packing factor0.74

Physical properties

Atomic radius: 136 pm
Ionization energy: 880 kJ/mol
Electron affinity: 151 kJ/mol
Crystal structure: Face-centered cubic (fcc)

Oxidation states

+3+4

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

2719 K4701 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

357.4nmIr I (UV)UV70%

380.1nmIr I (UV)UV100%

448.6nmIr I (blue)Violet40%

Dominant line 380.1 nmRange 357–449 nmTransitions 3