- Cerium (Ce) is a soft, silvery metallic element with atomic number 58, belonging to the lanthanide series in the periodic table.
- It is the most abundant of the rare earth elements, comprising about 0.0046% of the Earth’s crust—making it more common than tin and nearly as abundant as copper.
- Cerium has an electron configuration of [Xe] 4f¹ 5d¹ 6s², and it can lose either three or four electrons, giving it the unusual ability to exhibit both +3 and +4 oxidation states. Its atomic structure consists of fifty-eight protons, usually eighty-two or eighty-four neutrons, and fifty-eight electrons arranged in six shells.
- Naturally occurring cerium is composed primarily of the stable isotope cerium-140 (¹⁴⁰Ce), which makes up about 88.5% of its abundance, along with ¹³⁸Ce, ¹⁴²Ce, and trace amounts of radioactive ¹³⁶Ce.
- Cerium does not occur freely in nature but is found in several minerals, most notably monazite ((Ce,La,Nd,Th)PO₄) and bastnäsite ((Ce,La)(CO₃)F). These minerals, mined mainly in China, the United States, Brazil, and India, also contain other rare earth elements. Extraction of cerium involves complex chemical separation processes to distinguish it from its lanthanide neighbors.
- The element was discovered in 1803 independently by Swedish chemist Jöns Jacob Berzelius and his colleague Wilhelm Hisinger, as well as by German chemist Martin Heinrich Klaproth. It was named after the asteroid Ceres, which had been discovered just two years earlier in 1801.
- Cerium has numerous industrial and technological applications. One of its largest uses is in automotive catalytic converters, where cerium oxide (CeO₂) helps regulate the oxidation of carbon monoxide and hydrocarbons while storing and releasing oxygen to improve efficiency. Cerium oxide is also used in glass polishing powders, where its fine abrasiveness and chemical reactivity make it ideal for producing smooth, clear surfaces. In metallurgy, cerium is used as a component in mischmetal, an alloy employed in lighter flints. Cerium compounds are also used to decolorize glass, block ultraviolet light, and in self-cleaning oven coatings.
- Chemically, cerium is quite reactive for a rare earth metal. It tarnishes in air, forming a protective oxide layer, and reacts slowly with water. One of cerium’s distinctive properties is that it is the only rare earth element that can oxidize from +3 to +4 under mild conditions, making cerium(IV) oxide a strong oxidizing agent. This redox flexibility underpins many of its industrial uses, particularly in catalysis.
- Biologically, cerium has no known essential function in humans or other organisms. Most cerium compounds are of low toxicity, although fine cerium oxide dust can cause lung irritation upon inhalation.
- From an environmental perspective, cerium in its natural mineral form is stable and poses little hazard. However, mining and refining processes for cerium and other rare earth elements can produce significant environmental impacts, including chemical waste and radioactive by-products from thorium-containing ores.
