Cerium

Cerium is the most abundant of the rare earth elements, more common in the Earth's crust than copper, and is the active ingredient in self-cleaning ovens, polished glass, catalytic converters and the sparks from flint lighters.

• Atomic Number5858 protons, 58 electrons
• Atomic Mass140.116 u58× heavier than hydrogen
• State at Room TempSolidSolid
• Density6.770 g/cm³
• Melting / Boiling797.9°C / 3423.8°C
• Discovered1803

What is Cerium?

Cerium is a silvery-white lanthanide with 58 protons that can exist in both +3 and +4 oxidation states, making it versatile as a catalyst and oxidising agent. It is slightly radioactive, cerium-142 has an extremely long half-life.

Named after the dwarf planet Ceres, discovered just before the element in 1801. The element was discovered in 1803 by Jöns Jacob Berzelius and Wilhelm von Hisinger (and independently by Martin Klaproth).

Fact Cerium is more abundant in the Earth's crust than copper, approx. 66 parts per million vs copper's 68 ppm. Yet cerium is classified as a "rare earth" because it was historically difficult to separate from its mineral matrix.

Where you find Cerium

On Earth

China, USA, Australia, India (bastnäsite and monazite deposits).

How we use Cerium

• Cerium oxide paste polishes glass, optical lenses and silicon wafers, it is the primary glass-polishing compound worldwide.. Glass polishing
• Cerium oxide in catalytic converters stores and releases oxygen, helping the catalyst work under varying engine conditions.. Catalytic converters
• Cerium oxide coats self-cleaning oven walls, at high temperatures it catalyses the combustion of food residue, leaving only ash.. Self-cleaning ovens
• Mischmetal (a cerium-rich rare earth alloy) produces sparks in cigarette lighters and strikers: the material in a lighter flint.. Lighter flints

How it was discovered

Named after the dwarf planet Ceres, discovered just before the element in 1801. The element was discovered in 1803 by Jöns Jacob Berzelius and Wilhelm von Hisinger (and independently by Martin Klaproth).

Deeper dive: cerium and the lanthanide series

The lanthanides (elements 57-71) are characterised by the progressive filling of the 4f electron subshell. Because the 4f electrons are deep inside the atom and shielded by outer electrons, they have little effect on chemical bonding. All lanthanides have very similar chemical behaviour, forming +3 ions of comparable size. This similarity makes them extraordinarily difficult to separate from each other, historically requiring hundreds of fractional crystallisation steps. Ion exchange chromatography and solvent extraction methods, developed in the 1940s, finally made pure lanthanides available in quantity.

The term "rare earth" is historically misleading. Most lanthanides are as abundant as copper or nickel in the Earth's crust. The challenge is not scarcity but concentration: they are geochemically dispersed and rarely form rich mineral deposits. The name stuck from the 18th century when they were genuinely difficult to isolate.

Moving to 59 protons brings us to the next element in this remarkable family.