Chromium (Cr)

Shiny, hard metal

Chromium is the metal that gives stainless steel its mirror finish and ruby gems their deep red color, and with the anomalous configuration [Ar] 3d⁵ 4s¹ (half-filled d-shell stability), chromium has the highest oxidation state (+6) of any transition metal and is used in chrome plating and pigments.

Key metrics

Density7.19g/cm³

Melting point2,180K

Boiling point2,944K

Electronegativity1.66Pauling

Discovery

1797discovered

Discovered by: Louis Nicolas Vauquelin
Reactivity profile: Highly corrosion resistant
Reactivity: Low
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Ar]}\; \textcolor{#22c55e}{3_{d}^{5}}\; \textcolor{#ef4444}{4_{s}^{1}}

[Ar] 3d5 4s1

Wave function

\Psi_{\text{Cr}} \approx \frac{1}{\sqrt{24!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{24}(\mathbf{r}_{24}) \right|

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

Crystal structure

Body-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number8

Atoms per cell2

Atomic packing factor0.68

Physical properties

Atomic radius: 128 pm
Ionization energy: 653 kJ/mol
Electron affinity: 65 kJ/mol
Crystal structure: Body-centered cubic (bcc)

Oxidation states

+2+3+6

Acid/base

Can act as acid or base

Strongly acidicStrongly basic

State at 25 °CSolid

2180 K2944 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

427.5nmCr I (blue)Violet80%

520.8nmCr I (green)Green100%

541.9nmCr I (green)Green70%

Dominant line 520.8 nmRange 428–542 nmTransitions 3