Despite always occurring in combination with the other rare-earth elements in minerals such as those of the monazite and bastnäsite groups, cerium is easy to extract from its ores, as it can be distinguished among the lanthanides by its unique ability to be oxidized to the +4 state in aqueous solution.

It was discovered by Jöns Jakob Berzelius and Wilhelm Hisinger in 1803, and independently by Martin Heinrich Klaproth in Germany in the same year.

In 1839 Carl Gustaf Mosander separated cerium(III) oxide from other rare earths, and in 1875 William Francis Hillebrand became the first to isolate the metal.

[14] Like the other lanthanides, cerium metal is a good reducing agent, having standard reduction potential of E⦵ = −2.34 V for the Ce3+/Ce couple.

Such nuclei are called p-nuclei, and their origin is not yet well understood: some speculated mechanisms for their formation include proton capture as well as photodisintegration.

[23] The abundances of the cerium isotopes may differ very slightly in natural sources, because 138Ce and 140Ce are the daughters of the long-lived primordial radionuclides 138La and 144Nd, respectively.

The value of E⦵(Ce4+/Ce3+) varies widely depending on conditions due to the relative ease of complexation and hydrolysis with various anions, although +1.72 V is representative.

[15] Cerium(IV) oxide ("ceria") has the fluorite structure, similarly to the dioxides of praseodymium and terbium.

[34] Alkyl, alkynyl, and alkenyl organocerium derivatives are prepared from the transmetallation of the respective organolithium or Grignard reagents, and are more nucleophilic but less basic than their precursors.

[35][36] Cerium was discovered in Bastnäs in Sweden by Jöns Jakob Berzelius and Wilhelm Hisinger, and independently in Germany by Martin Heinrich Klaproth, both in 1803.

It was not until Carl Gustaf Mosander succeeded in removing lanthana and "didymia" in the late 1830s that ceria was obtained pure.

[39][40][41][42] The element played a role in the Manhattan Project, where cerium compounds were investigated in the Berkeley site as materials for crucibles for uranium and plutonium casting.

[50][47] Cerium is the easiest lanthanide to extract from its minerals because it is the only one that can reach a stable +4 oxidation state in aqueous solution.

[54] Bastnäsite, LnIIICO3F, is usually lacking in thorium and the heavy lanthanides beyond samarium and europium, and hence the extraction of cerium from it is quite direct.

After separation, it is treated with hot concentrated sulfuric acid to produce water-soluble sulfates of rare earths.

[56] The first use of cerium was in gas mantles, invented by Austrian chemist Carl Auer von Welsbach.

In 1885, he had previously experimented with mixtures of magnesium, lanthanum, and yttrium oxides, but these gave green-tinted light and were unsuccessful.

[citation needed] This resulted in commercial success for von Welsbach and his invention, and created great demand for thorium.

[59] Applications were soon found for them, especially in the pyrophoric alloy known as "mischmetal" composed of 50% cerium, 25% lanthanum, and the remainder being the other lanthanides, that is used widely for lighter flints.

[51] This property of cerium saved the life of writer Primo Levi at the Auschwitz concentration camp, when he found a supply of ferrocerium alloy and bartered it for food.

[38] The addition of cerium oxide to older cathode-ray tube television glass plates was beneficial, as it suppresses the darkening effect from the creation of F-center defects due to the continuous electron bombardment during operation.

Cerium is also an essential component as a dopant for phosphors used in CRT TV screens, fluorescent lamps, and later white light-emitting diodes.

[63][64] The most commonly used example is cerium(III)-doped yttrium aluminium garnet (Ce:YAG) which emits green to yellow-green light (550–530 nm) and also behaves as a scintillator.

[65] Cerium salts, such as the sulfides Ce2S3 and Ce3S4, were considered during the Manhattan Project as advanced refractory materials for the construction of crucibles which could withstand the high temperatures and strongly reducing conditions when casting plutonium metal.

These Al-Ce alloys have excellent high temperature strength and are suitable for automotive applications (e.g. in cylinder heads).

[67] Other automotive applications for the lower sesquioxide are as a catalytic converter for the oxidation of CO and NOx emissions in the exhaust gases from motor vehicles.

[68][69] The early lanthanides have been found to be essential to some methanotrophic bacteria living in volcanic mudpots, such as Methylacidiphilum fumariolicum: lanthanum, cerium, praseodymium, and neodymium are about equally effective.

Cerium is more dangerous to aquatic organisms because it damages cell membranes; it is not very soluble in water and can cause environmental contamination.

[79] Elemental cerium has no established occupational or permissible exposure limits by the OSHA or American Conference of Governmental Industrial Hygienists, though it is classified as a flammable solid and regulated as such under the Globally Harmonized System of Classification and Labelling of Chemicals.

[82] Toxicological reports on cerium compounds have noted their cytotoxicity[79] and contributions to pulmonary interstitial fibrosis in workers.