Cobalt
Element 27 · Transition Metal
Cobalt is a hard, lustrous, magnetic transition metal whose name comes from the German kobold, meaning goblin — medieval miners blamed mischievous spirits for its arsenic-laced ores. For centuries its main fame was cobalt blue, the deep pigment in glass, porcelain, and paintings.
Today cobalt is a strategic metal: lithium cobalt oxide powers phone and laptop batteries, cobalt superalloys survive inside jet engines, and a single cobalt atom sits at the heart of vitamin B12, essential for human nerves and red blood cells.
Key facts
| Atomic number | 27 |
|---|---|
| Atomic weight | 58.933 |
| Category | Transition Metal |
| Group / Period | 9 / 4 |
| Block | d |
| Electron configuration | [Ar] 3d7 4s2 |
| Common oxidation states | +3, +2 |
| State at STP | Solid |
| Electronegativity | 1.88 |
| Atomic radius | 152 pm |
| Density | 8.90 g/cm³ |
| Melting point | 1495 °C |
| Boiling point | 2927 °C |
Occurrence
Cobalt usually occurs alongside nickel and copper ores in minerals such as cobaltite and erythrite, and is recovered as a byproduct of their mining. The Democratic Republic of the Congo produces the majority of the world's supply. It never occurs as a free metal in nature.
Applications
Lithium-ion batteries use lithium cobalt oxide cathodes
Superalloys for jet turbine blades rely on cobalt's heat resistance
Cobalt-blue pigments and glass have colored art for centuries
Vitamin B12, essential for nerves and blood, contains one cobalt atom
Alnico and samarium-cobalt magnets serve in motors and sensors
Common compounds
- cobalt chloride
- cobalt oxide
- lithium cobalt oxide
- cobalt nitrate
Cobalt is the only metal whose compounds turn from blue to pink as they absorb water.
Data source: IUPAC standard atomic weights 2021