Cerium (Ce)

Cerium is the most abundant rare earth, more common in the crust than copper, which makes the name "rare earth" a historical accident: they were called rare because they were hard to separate, not because there is little of them. It is the only lanthanide with a stable +4 state, which is what lets a catalytic converter store and release oxygen as the engine's mixture swings rich and lean. A lighter flint is mostly cerium: the alloy is soft and pyrophoric, so a struck spark is a shaving of metal burning in mid-air.

Properties

Atomic number

58

Symbol

Ce

Standard atomic weight

140.12 u

Category

Lanthanide

Period

6

Block

f-block

Electron configuration

[Xe] 6s² 4f¹ 5d¹

Electrons per shell

2, 8, 18, 19, 9, 2

Melting point

1,071 K — 797.9 °C — 1468.1 °F

Boiling point

3,697 K — 3423.8 °C — 6194.9 °F

Density

6.77 g/cm³

Electronegativity

1.12 (Pauling)

Oxidation states

+4, +3

Discovered

1803 by Jöns Jacob Berzelius and Wilhelm Hisinger, and independently Martin Heinrich Klaproth

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹ 5d¹

Noble gas shorthand

[Xe] 6s² 4f¹ 5d¹

Shells

K: 2 · L: 8 · M: 18 · N: 19 · O: 9 · P: 2

What it is used for

• Glass and silicon wafer polishing — cerium oxide is the standard abrasive
• The oxygen buffer in three-way catalytic converters
• Lighter flints, as the main component of mischmetal
• UV-absorbing glass for car windows and display cases
• Self-cleaning oven coatings

Hazards

• Cerium metal turnings are pyrophoric and can ignite from friction alone

Anomalous electron configuration: [Xe] 6s² 4f¹ 5d¹ rather than the predicted 6s² 4f². Named after the asteroid Ceres, discovered two years earlier.

Neighbours in the table