Cobalt
[Ar] 3d⁷ 4s² · 2 · 8 · 15 · 2
A ferromagnetic metal with the highest Curie point of any element, 1394 K. Cobalt has given glass and ceramics a deep blue for millennia, and today it sits in the cathode of nearly every lithium-ion battery.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 27
- Atomic mass
- 58.933 а.е.м.
- Electron configuration
- [Ar] 3d⁷ 4s²
- Electrons per shell
- 2 · 8 · 15 · 2
- Block
- d-block
- Group
- Cobalt group
- Period
- 4
- Electronegativity (Pauling)
- 1.88
- Electronegativity (Allen)
- 1.84
- Atomic radius
- 152 pm
- Covalent radius
- 126 pm
- Van der Waals radius
- 192 pm
- Ionisation energy 1
- 760.4 kJ/mol
- Ionisation energy 2
- 1 648 kJ/mol
- Ionisation energy 3
- 3 232 kJ/mol
- Ionisation energy 4
- 4 950 kJ/mol
- Ionisation energy 5
- 7 670 kJ/mol
- Electron affinity
- 63.7 kJ/mol
- Common oxidation states
- +2, +3
- Oxidation states
- -3, -1, +1, +2, +3, +4, +5
Physical properties
- State at 25 °C
- solid
- Density
- 8.9 g/cm³
- Melting point
- 1 768 K · 1 494.9 °C
- Boiling point
- 3 200 K · 2 926.9 °C
- Speed of sound
- 4 720 m/s
Thermal properties
- Heat of fusion
- 16.06 kJ/mol
- Heat of vaporisation
- 377 kJ/mol
- Specific heat capacity
- 0.421 J/(g·K)
- Thermal conductivity
- 100 W/(m·K)
Mechanical properties
- Young's modulus
- 209 GPa
- Shear modulus
- 75 GPa
- Bulk modulus
- 180 GPa
- Poisson ratio
- 0.31
- Mohs hardness
- 5
- Brinell hardness
- 700 MPa
Electrical and magnetic properties
- Electrical resistivity
- 62.4 nΩ·m
- Magnetic ordering
- ferromagnetic
- Curie point
- 1 394 K
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 250.71 pm · c = 406.95 pm
Abundance
- In the crust
- 25 mg/kg
- In the ocean
- 2·10⁻⁵ mg/L
- In the universe
- 3 000 mg/kg
- In the human body
- 0.02 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 59Co | 100 % | stable | — |
| 60Co | — | 5.27 yr | β− |
Cobalt-60, half-life 5.27 years, is among the most widely used industrial gamma sources, in medicine, radiography and sterilisation.
Discovery
- Year of discovery
- 1735
- Discovered by
- Georg Brandt
- Where
- Sweden
- Origin of the name
- from German Kobold, the goblin blamed for ore that yielded no metal
History
The name comes from the German Kobold, the mine goblin Saxon miners blamed for ores that yielded no copper and poisoned smelters with arsenic fume. Georg Brandt showed in 1735 that the blue came from a new element, not from bismuth.
Where it occurs
25 mg/kg of the crust. Ores of its own barely exist; cobalt is won alongside copper and nickel. More than half of world output comes from the Democratic Republic of the Congo.
How it is produced
Hydrometallurgically from copper and nickel concentrates. A significant share of Congolese output is artisanal, which is the source of the industry's well-known ethical problem.
Role in living things
The only metal in vitamin B₁₂: a cobalt atom at the centre of a corrin ring. Without B₁₂ neither DNA nor myelin can be made, and only bacteria know how to synthesise it.
Safety
Cobalt dust causes asthma and lung fibrosis; cobalt-bearing implants can cause systemic toxicity as they wear.
Uses
- Lithium-ion battery cathodes — the largest modern use
- Heat-resistant superalloys for gas turbine blades
- Cemented carbides: cobalt binds the tungsten carbide grains
- Cobalt blue in glass, glaze and paint
- Cobalt-60 in radiotherapy and sterilisation
Curiosities
- Cobalt glass is that deep blue known from Egyptian and Mesopotamian work.
- Cobalt's Curie point beats iron's and nickel's — it stays magnetic to 1121 °C.
- The name literally means evil spirit of the mine.
- Vitamin B₁₂ is the only biomolecule with a metal–carbon bond.