Cobalt (Co)

Hard, magnetic metal

Cobalt is a hard, magnetic metal used in lithium-ion batteries, jet engines, and the vivid blue of ancient pottery, and with [Ar] 3d⁷ 4s², cobalt has strong ferromagnetic properties and is used in Alnico magnets and superalloys. Vitamin B₁₂ contains a cobalt ion at its core.

Key metrics

Density8.9g/cm³

Melting point1,768K

Boiling point3,200K

Electronegativity1.88Pauling

Discovery

1735discovered

Discovered by: Georg Brandt
Reactivity profile: Stable in air
Reactivity: Low
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Ar]}\; \textcolor{#22c55e}{3_{d}^{7}}\; \textcolor{#ef4444}{4_{s}^{2}}

[Ar] 3d7 4s2

Wave function

\Psi_{\text{Co}} \approx \frac{1}{\sqrt{27!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{27}(\mathbf{r}_{27}) \right|

Probability density $|\Psi|^2$ across the Co 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: 125 pm
Ionization energy: 760 kJ/mol
Electron affinity: 63 kJ/mol
Crystal structure: Hexagonal close-packed (hcp)

Oxidation states

+2+3

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

1768 K3200 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

411.9nmCo IViolet95%

412.2nmCo I (violet)Violet100%

527.8nmCo I (green)Green60%

Dominant line 412.2 nmRange 412–528 nmTransitions 3