Cobalt (Co)
“Cursed by Saxon miners as a goblin’s trick, this demon-named metal now powers your phone battery and fires gamma rays into tumours.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- Configuration [Ar] 3d⁷ 4s² — a Period 4, Group 9 transition metal; the Co²⁺ ion, with its two 4s electrons gone, is the hero of its chemistry.
- Its compounds wear the most intense blue in the mineral world: cobalt(II) dissolved in glass, glaze and porcelain yields the deep “cobalt blue” of Chinese vases and Persian tiles.
- Ferromagnetic like iron, and its magnetism survives to a higher temperature than any other metal’s — the Curie point of cobalt is about 1,115 °C.
- At the centre of vitamin B₁₂ sits a single cobalt atom — the only vitamin built around a metal; without it nerves degenerate and pernicious anaemia follows.
A hard, lustrous, silver-grey metal with a faint bluish tone, sitting between iron and nickel in look and strength. It is strongly magnetic, takes a fine polish and resists corrosion — a tough, no-nonsense metal you would mistake for steel until its compounds blaze out in impossible blues.
Where you meet it
✦ Uses
- Lithium-cobalt-oxide (LiCoO₂) cathodes — the rechargeable battery of most smartphones and laptops holds a slab of cobalt chemistry at its heart.
- Cobalt-60 radiotherapy — cancer hospitals across Bangladesh aim beams of gamma rays from cobalt-60 machines at tumours, and the same isotope sterilises surgical instruments.
- Cobalt-blue glaze and glass — potters and glassmakers paint with cobalt compounds for that unbeatable deep blue; a trace in a melt turns the whole batch sapphire.
- Superalloys and magnets — jet-engine turbine blades and heat-proof power-station alloys lean on cobalt, while Alnico magnets (aluminium-nickel-cobalt) stay strong to high temperatures.
◍ Everyday examples
- The phone in your pocket — its battery very likely holds a few grams of cobalt, most of it mined in the Democratic Republic of Congo.
- The fish, meat, eggs and liver of a Bengali plate supply the B₁₂ whose cobalt centre keeps nerves and blood cells in order.
- A deep-blue glazed pot, a mosque tile or an old blue bottle — each owes its colour to a pinch of cobalt.
History & name
Silver miners in Saxony knew a hateful blue-grey ore: it looked rich, gave off poisonous arsenic fumes when roasted, and yielded no silver at all. They blamed Kobold, the goblin said to haunt the mountains and steal the metal, and the insult stuck to the ore itself. In 1735 the Swedish chemist Georg Brandt — investigating why that ore turned glass a glorious deep blue — proved the colour came from a metal no ancient writer had ever known, and isolated it; he kept the miners’ name, Latinised as cobaltum. It was the first metal discovered since antiquity, and the first whose name tells a ghost story. The blue itself was already ancient: Chinese potters and Persian tile-makers had been painting with cobalt for centuries without knowing what burned inside it.