Cerium
Cerium is a chemical element with symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet Ceres (itself named after the Roman goddess of agriculture).
Identity
- Atomic mass
- 140.116 u
- Category
- Lanthanides
- Group
- 3
- Period
- 6
- Block
- f
- Oxidation States
- +3, +4
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1 4f1
- Short configuration
- [Xe] 4f1 5d1 6s2
- Electrons per shell
- 2, 8, 18, 19, 9, 2
- Electronegativity (Pauling)
- 1.12
- Electron affinity
- 55 kJ/mol
- 1st ionization energy
- 534 kJ/mol
- Ionization energies
- 534 · 1050 · 1949 · 3547 · 6325… kJ/mol
Physical properties
- Melting point
- 794.9 °C (1068 K)
- Boiling point
- 3442.8 °C (3716 K)
- Density
- 6.77 g/cm³
- Molar heat capacity
- 26.9 J/(mol·K)
Chemical behavior of cerium
Cerium has four outer electrons ([Xe] 4f¹ 5d¹ 6s²) and is the only lanthanide with a stable +4 state in addition to the usual +3. Its electronegativity is very low (1.12) and its chemistry is redox: the Ce³⁺/Ce⁴⁺ pair gives up and takes up oxygen with ease. It is strongly reducing, pyrophoric in fine powder and oxidizes rapidly in air. That ability to store oxygen makes it unique among the rare earths.
Reactivity
Ce + O₂ → CeO₂
In air it rapidly forms cerium(IV) oxide, which is very stable. When heated, the metal burns with brilliant sparks: this is the basis of ferrocerium lighter flints.
2 Ce + 6 H₂O → 2 Ce(OH)₃ + 3 H₂
It reacts with water to form cerium(III) hydroxide and hydrogen. The hydroxide then oxidizes in air to cerium(IV) oxide.
2 Ce + 6 HCl → 2 CeCl₃ + 3 H₂
It dissolves in dilute acids to give cerium(III) salts. With strong oxidants it goes to cerium(IV) salts, deep orange in color.
CeO₂ + 4 HCl → CeCl₃ + Cl₂ + 2 H₂O
Cerium(IV) oxide is an oxidant: with concentrated hydrochloric acid it releases chlorine. Cerium(IV) sulfate is used as a titrant oxidant in chemical analysis.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Cerium oxide | CeO₂ | Catalysts, glass polishing and converters |
| Ferrocerium | Ce-Fe | Lighter flints and sparks |
| Cerium(IV) sulfate | Ce(SO₄)₂ | Oxidant in chemical analysis |
| Cerium fluoride | CeF₃ | Cinema arcs and scintillation detectors |
| Cerium ammonium nitrate | (NH4)2Ce(NO3)6 | Oxidant in organic synthesis |
Electron shell distribution
View in the atom builderIsotopes
Natural cerium mixes four stable isotopes: cerium-140 (¹⁴⁰Ce, ~88.45%), cerium-142 (~11.11%), cerium-138 (~0.25%) and cerium-136 (~0.19%), all with 58 protons. ¹⁴⁰Ce dominates and defines its atomic mass. ¹⁴²Ce decays extremely slowly and is used in geochronological studies of ancient rocks.
Occurrence and production
It is the most abundant lanthanide, at about 66 ppm in the crust, more than copper or lead. It occurs in bastnasite and monazite alongside lanthanum and neodymium. The major deposits are in Bayan Obo (China), Mountain Pass (United States) and Mount Weld (Australia). It is obtained by acid dissolution, solvent extraction and separation of the Ce(IV)/Ce(III) pair by selective oxidation.
History and origin of the name
Martin Heinrich Klaproth and, separately, Berzelius and Hisinger identified it in 1803 in ceria and named it cerium after Ceres, the dwarf planet discovered two years earlier. Mosander showed in 1839 that ceria also hid lanthanum and didymium. During the 20th century, Auer von Welsbach's ferrocerium carried it into every pocket in the form of a lighter flint.
Applications and relevance of cerium
Uses of the element
As a metal it goes into the ferrocerium of lighter flints and into pyrophoric alloys, and as an additive in steels, castings and magnesium alloys. Its great affinity for oxygen makes it useful as a deoxidizer and desulfurizer in metallurgy.
Uses of its compounds
Cerium oxide is the heart of catalytic converters, of glass and screen polishing, and of sunscreens as a UV filter. Doped with other lanthanides it produces yellow phosphors for white LEDs, and as a solid electrolyte it conducts oxygen in fuel cells.
Health, safety and environment
Biological role
It has no biological function and its absorption is very low. Cerium oxide is used in cosmetics and polishing with no relevant toxicity, although chronic inhalation of fine dust can irritate the airways like any mineral dust.
Safety
The metal in fine powder is pyrophoric and can burn in air, so it is stored and handled under an inert atmosphere in industry. Ferrocerium generates sparks on purpose, but in lighters the risk is minimal with normal use.
Environment
Its mining shares the impacts of the rare earths: tailings ponds and mobilization of thorium and uranium if not managed. In use it is beneficial: cerium-containing catalysts reduce car emissions and polishing with the oxide avoids harsh solvents.
Frequently asked questions about Cerium
What is cerium used for in cars?
Cerium plays a key role in the catalytic converters of petrol vehicles. Its oxide can store and release oxygen depending on exhaust conditions, helping to convert carbon monoxide and unburnt hydrocarbons into carbon dioxide and water. This ability to "regulate" oxygen improves the catalyst's efficiency and helps reduce harmful emissions. That is why cerium is fundamental to automotive emissions-control technology.
Is cerium responsible for the sparks in lighters?
Yes, to a large extent. The flint of many lighters and pocket lighters is made of ferrocerium, an alloy containing cerium and iron, among other metals. When scraped, it produces tiny, highly reactive particles that oxidize quickly and generate sparks sufficient to light gas or a wick. It is one of the best-known applications of cerium and a good example of how its pyrophoric properties are exploited in an everyday object.
Where is cerium found and how is it obtained?
Cerium is the most abundant lanthanide and is found in minerals such as bastnasite and monazite, usually alongside other rare-earth elements. To obtain it, the ore is crushed and processed by acid dissolution, solvent extraction and ion exchange, stages that allow each metal to be separated. Compounds such as cerium oxide or the pure metal can then be produced. Its relative abundance makes it one of the most widely used lanthanides industrially.
Why is cerium so important in chemistry and industry?
Its importance comes from its ability to switch between oxidation states, especially +3 and +4. This lets it give up and take up oxygen with ease, a property that is highly valuable in catalysis, gas purification, surface polishing, ceramics and energy storage. It is also relatively abundant compared with other lanthanides, which makes large-scale use viable. This combination of chemical versatility and availability explains its presence in technologies as different as cars, optics and lighting.
Why is cerium oxide used to polish glass?
Cerium oxide is one of the most effective abrasives for fine polishing of glass, lenses, mirrors and screens. It works through a combination of mechanical and chemical action: it removes microscopic irregularities and helps produce very transparent surfaces without visible scratches. It is used in the manufacture of eyeglasses, camera lenses, optical instruments and electronic components. Its effectiveness explains why it remains a benchmark material in precision optics.
Is it dangerous to touch or handle cerium?
Metallic cerium can react with air and, in the form of fine powder, present a fire hazard, so its handling is restricted to industrial settings with safety measures. Common compounds such as cerium oxide are far more stable and are used in consumer products, although they should not be inhaled as dust. For the average person, contact with objects containing cerium is not a significant exposure; the risks depend on the chemical form and the concentration.
What does cerium have to do with white LED lights?
Some cerium-doped phosphors emit yellow light when they receive blue light from an LED chip. By combining that yellow emission with the remaining blue light, a light perceived as white is produced. This principle is behind much of today's commercial LED lighting. Cerium is not the main light source, but it acts as an essential color converter that lets LED bulbs deliver useful, efficient white light.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.