Lanthanum
Lanthanum is a soft, ductile, silvery-white metallic chemical element with symbol La and atomic number 57. It tarnishes rapidly when exposed to air and is soft enough to be cut with a knife. It gave its name to the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table:it is also sometimes considered the first element of the 6th-period transition metals.
Identity
- Atomic mass
- 138.905 u
- Category
- Lanthanides
- Group
- 3
- Period
- 6
- Block
- f
- Oxidation States
- +3
- Phase (25 °C)
- Solid
- Appearance
- silvery white
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1
- Short configuration
- [Xe] 5d16s2
- Electrons per shell
- 2, 8, 18, 18, 9, 2
- Electronegativity (Pauling)
- 1.10
- Electron affinity
- 53 kJ/mol
- 1st ionization energy
- 538 kJ/mol
- Ionization energies
- 538 · 1067 · 1850 · 4819 · 5940 kJ/mol
Physical properties
- Melting point
- 919.9 °C (1193 K)
- Boiling point
- 3463.8 °C (3737 K)
- Density
- 6.162 g/cm³
- Molar heat capacity
- 27.1 J/(mol·K)
Chemical behavior of lanthanum
Lanthanum has three outer electrons ([Xe] 5d¹ 6s²) and a very low electronegativity (1.10), so it almost always acts as +3, forming bonds with a markedly ionic character. It is a very electropositive and reducing metal: it oxidizes rapidly in air, reacts with water and dissolves readily in dilute acids. Its La³⁺ ion, large and with no f electrons, is the reference for the entire lanthanide series.
Reactivity
4 La + 3 O₂ → 2 La₂O₃
Exposed to air it tarnishes rapidly and, when heated, burns to form lanthanum oxide. The metal must be stored under an inert atmosphere or in mineral oil.
2 La + 6 H₂O → 2 La(OH)₃ + 3 H₂
It reacts slowly when cold and more vigorously when hot, forming a poorly soluble hydroxide and releasing hydrogen.
2 La + 6 HCl → 2 LaCl₃ + 3 H₂
It dissolves readily in dilute acids to give lanthanum(III) salts. This is the usual route to lanthanum chlorides and nitrates as starting materials.
2 La + 3 Cl₂ → 2 LaCl₃
With the halogens it reacts on heating to give ionic trihalides. The chloride is the raw material for producing the metal by electrolysis of molten salts.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Lanthanum oxide | La₂O₃ | Optical glasses and refinery catalysts |
| Lanthanum hexaboride | LaB₆ | Emission cathodes in electron microscopes |
| Lanthanum–nickel alloy | LaNi₅ | Hydrogen storage in NiMH batteries |
| Lanthanum carbonate | La₂(CO₃)₃ | Phosphate-chelating drug in kidney dialysis |
| Lanthanum chloride | LaCl₃ | Production of the metal and catalysts |
Electron shell distribution
View in the atom builderIsotopes
Natural lanthanum is a mixture of lanthanum-139 (¹³⁹La), with 82 neutrons and 99.91%, which is stable, and lanthanum-138 (¹³⁸La), with 81 neutrons and 0.09%, a primordial radionuclide with a half-life of about 1.02 × 10¹¹ years. The decay of ¹³⁸La to barium and cerium is used in the geological dating of rocks and meteorites.
Occurrence and production
It is relatively abundant in the crust, at about 39 ppm, but never appears native: it is found in bastnasite and monazite, together with cerium, neodymium and other lanthanides. The main deposits are in China, the United States and Australia. It is obtained by acid dissolution of the ore followed by solvent extraction and ion exchange, and the metal by electrolysis of molten chlorides or reduction with calcium.
History and origin of the name
Carl Gustaf Mosander separated it in 1839 from the impure ceria of Berzelius and named it lanthanum, from the Greek lanthanein (to lie hidden), because it had remained hidden in cerium oxide. The complete separation of the rare earths took decades because of their close chemical similarity. Carl Auer von Welsbach obtained high-purity samples at the end of the 19th century and gave the entire lanthanide series its name.
Applications and relevance of lanthanum
Uses of the element
As a metal it is part of mischmetal for lighter flints, steels and castings, and of LaNi₅ alloys that store hydrogen in the nickel-metal hydride rechargeable batteries of hybrid vehicles. It is also added to steels and alloys to improve malleability and strength.
Uses of its compounds
The oxide is added to high-refractive-index glasses for camera, telescope and microscope lenses, and to petroleum-cracking catalysts. The hexaboride serves as an electron emitter in microscopy, and the carbonate as a medicine to control phosphate in kidney patients.
Health, safety and environment
Biological role
It has no known biological function and is barely absorbed by the oral route. Lanthanum carbonate is used as a prescription drug to reduce phosphate absorption in advanced kidney disease, with medical follow-up because of its potential accumulation.
Safety
The metal in filings or fine powder can ignite in air and reacts with moisture, so it is handled in industrial settings under an inert atmosphere and with dust protection. The compounds typically found in finished products are stable and do not pose significant exposure for the user.
Environment
Its main impact comes from rare-earth mining: large volumes of rock, reagent consumption and waste containing associated thorium and uranium that must be managed. Recycling from batteries, optics and catalysts is still limited but growing because of its strategic value.
Frequently asked questions about Lanthanum
What is lanthanum used for in everyday life?
Lanthanum is present, indirectly, in everyday objects and technologies. Its compounds improve the optical lenses of cameras and telescopes, take part in refinery catalysts, and form part of the nickel-metal hydride batteries used in hybrid vehicles. It is also used in alloys for lighters and in hydrogen-storage materials. Although it rarely appears by name on a product, it contributes to the efficiency of optics, energy and mobility.
Where is lanthanum found in nature?
Lanthanum does not occur free in nature; it is part of rare-earth minerals such as bastnasite and monazite. It is obtained mainly as a by-product of the processing of these ores, together with cerium, neodymium and other lanthanides. Although it is classed as a "rare earth", it is not especially scarce in the Earth's crust; the difficulty lies in finding profitable deposits and separating it from chemically very similar elements.
What role does lanthanum play in hybrid car batteries?
Lanthanum is part of the alloys used in the nickel-metal hydride rechargeable batteries found in many hybrid vehicles. These alloys can absorb and release hydrogen reversibly, a process essential to storing energy during charging and returning it while driving. Their use helps improve the battery's capacity, durability and behavior, especially under the frequent charge and discharge cycles typical of city driving.
What is the difference between lanthanum and the lanthanides?
Lanthanum is a specific chemical element, with the symbol La and atomic number 57. The lanthanides, by contrast, are a series of 15 metallic elements running from lanthanum to lutetium. Lanthanum is usually considered the first member of that series and shares with them the rare-earth metal character, the tendency to form the +3 oxidation state and the occurrence in similar minerals. The difference, therefore, is the one between an individual member and its whole chemical family.
Is lanthanum dangerous to health?
Pure metallic lanthanum does not occur naturally in the everyday environment and can react with air and moisture, so its handling requires industrial precautions. Lanthanum carbonate, by contrast, is a prescription medicine used to reduce phosphate absorption in people with advanced kidney disease. For the general public, the relevant exposure does not come from the isolated element but from specific products and medications that must be used as directed by a professional.
Why is lanthanum considered a rare earth if it is not that scarce?
The term "rare earth" is historical and can be misleading: it does not mean the element is necessarily rare, but that it belongs to a group of metals with similar properties that are hard to separate. Lanthanum is relatively abundant, but it is scattered through minerals and almost always mixed with other lanthanides. Its production requires complex extraction, purification and separation processes, which explains its strategic value and its geographic concentration in certain mines.
Why is lanthanum used in lenses and optical glasses?
Lanthanum oxide is added to special glasses to modify their refractive index and improve optical properties without making them excessively heavy or dispersive. This allows more compact lenses with better correction of aberrations, useful in cameras, microscopes, telescopes and scientific instrumentation. It can also improve the glass's resistance to alkaline media. For this reason, lanthanum is a valuable component in precision optics.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.