Rhodium (Rh)

Silvery-white metal

Rhodium is the most expensive precious metal, coating catalytic converters to clean exhaust fumes, and with [Kr] 4d⁸ 5s¹, rhodium is one of the rarest elements in Earth's crust (0.001 ppm). It converts 90%+ of harmful NOₓ, CO, and hydrocarbons in car exhaust into harmless gases.

Key metrics

Density12.41g/cm³

Melting point2,237K

Boiling point3,968K

Electronegativity2.28Pauling

Discovery

1803discovered

Discovered by: William Hyde Wollaston
Reactivity profile: Highly corrosion resistant
Reactivity: Low
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Kr]}\; \textcolor{#22c55e}{4_{d}^{8}}\; \textcolor{#ef4444}{5_{s}^{1}}

[Kr] 4d8 5s1

Wave function

\Psi_{\text{Rh}} \approx \frac{1}{\sqrt{45!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{45}(\mathbf{r}_{45}) \right|

Probability density $|\Psi|^2$ across the Rh 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: 134 pm
Ionization energy: 720 kJ/mol
Electron affinity: 110 kJ/mol
Crystal structure: Face-centered cubic (fcc)

Oxidation states

+1+3

Acid/base

Neutral

Strongly acidicStrongly basic

State at 25 °CSolid

2237 K3968 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

369.2nmRh I (UV)UV50%

437.5nmRh I (blue)Violet100%

450.7nmRh IBlue70%

Dominant line 437.5 nmRange 369–451 nmTransitions 3