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Cerium (Ce) is a chemical element with atomic number 58 in the lanthanide series of the periodic table. It is the most abundant of the rare earth elements in the Earth's crust and is used in a variety of applications because it can exist in the +3 and +4 oxidation states.

Discovery and name: Cerium was identified in 1803 by the Swedish chemists Jöns Jacob Berzelius and Wilhelm Hisinger from the mineral cerite; the name derives from Ceres, the Roman goddess and the dwarf planet.

Isolation and properties: The metal was first isolated in 1831 by Friedrich Wöhler. Cerium is a soft, silvery-white metal that readily tarnishes in air. It forms oxides, notably cerium(IV) oxide (CeO2), and is used as an oxygen storage material and catalyst support. The Ce4+/Ce3+ redox couple underpins much of its chemical versatility.

Occurrence and production: Cerium occurs widely in minerals such as bastnäsite and monazite. It is commercially recovered as a major component of rare earth oxide concentrates, with leading producers including China, the United States, Australia and others. Global supply chains reflect the importance of rare earth processing for modern technologies.

Applications and uses: Cerium compounds are used in petroleum refining catalysts and automotive catalytic converters, where CeO2 acts as an oxygen storage material. It is also employed in glass polishing powders, ceramics and certain alloys. Mixed rare-earth alloys containing cerium have uses in specialty applications such as lighter flints and specialized coatings.

Isotopes: Cerium has several isotopes; four are stable—136Ce, 138Ce, 140Ce, and 142Ce. A radioactive isotope, 144Ce, has been produced for research and medical applications.