Lanthanum is the chemical element with symbol La and atomic number 57. It is a soft, silvery rare-earth metal that begins the lanthanide series. Lanthanum tarnishes quickly in air and is normally found combined with other rare-earth elements in minerals such as monazite and bastnäsite.
Lanthanum quick facts
| Property | Value |
| Symbol | La |
| Atomic number | 57 |
| Relative atomic mass | 138.905 |
| Period | 6 |
| Block | d-block / lanthanide boundary |
| Density | 6.15 g/cm³ |
| Melting point | 920°C |
| Boiling point | 3464°C |
| Electron configuration | [Xe] 5d¹ 6s² |
| Common oxidation state | +3 |
| CAS number | 7439-91-0 |
| Key isotope | ¹³⁹La |
Chemistry and occurrence
Lanthanum chemistry is dominated by the La³⁺ ion. The metal reacts with oxygen and water and burns readily when strongly heated. Commercial lanthanum is separated from mixed rare-earth concentrates by ion exchange or solvent extraction.
See the complete CleverlySmart periodic table.
Important compounds and uses
- Lanthanum oxide (La₂O₃): added to high-index optical glass for camera lenses and other optics.
- Lanthanum-nickel alloys: can reversibly store hydrogen and are related to nickel-metal-hydride battery technology.
- Petroleum catalysts: lanthanum compounds improve the thermal stability of cracking catalysts.
- Mischmetal: rare-earth alloy mixtures containing lanthanum are used in lighter flints and metallurgical additives.
- Lanthanum carbonate: used medically as a phosphate binder under prescription for some patients with chronic kidney disease.
Lanthanum isotopes
Natural lanthanum is almost entirely stable ¹³⁹La, with a small fraction of extremely long-lived radioactive ¹³⁸La. For broader isotope data, see the CleverlySmart isotope table.
Biological role and safety
Lanthanum has no known essential biological role. The metal and many compounds have relatively low acute toxicity, but dusts and soluble salts still require appropriate occupational controls.
Discovery and name
Carl Gustav Mosander discovered lanthanum in 1839 while separating components of cerium compounds. Its name comes from the Greek lanthanein, meaning “to lie hidden,” reflecting how it had been concealed within another rare-earth material.
Lanthanum key data
| Atomic number | 57 |
| Standard atomic weight | 138.90547 |
| Electron configuration | [Xe] 5d¹ 6s² |
| Melting point | 920 °C (1,688 °F) |
| Boiling point | 3,464 °C (6,267 °F) |
| Density | 6.15 g/cm³ |
| Common oxidation state | +3 |
Lanthanum is a soft, silvery rare-earth metal that quickly tarnishes in air. It is usually grouped with the lanthanides and is important mainly through its compounds and alloys rather than as bulk pure metal.
Chemistry and important compounds
Lanthanum chemistry is dominated by the +3 oxidation state. Important compounds include lanthanum oxide (La₂O₃), lanthanum chloride (LaCl₃) and lanthanum carbonate. La₂O₃ is used in specialty glass and ceramics, while lanthanum-containing materials also appear in catalysts and advanced electrode materials.
Where lanthanum is used
- Optical glass: lanthanum compounds help produce high-refractive-index glass used in precision lenses.
- Nickel-metal hydride batteries: lanthanum-rich alloys can store hydrogen and are used in battery electrode materials.
- Catalysts: lanthanum compounds are used to modify selected petroleum-refining and emissions-control catalyst systems.
- Mischmetal and alloys: lanthanum is a component of rare-earth alloys used in lighter flints and specialty metallurgy.
Isotopes
Natural lanthanum is overwhelmingly lanthanum-139. A small amount of lanthanum-138 also occurs naturally and is extremely long-lived, with a half-life of about 1.06 × 10¹¹ years. For isotope terminology and half-life tables, see our complete isotope table guide.
Safety and handling
Fresh lanthanum metal is reactive and oxidizes in air. Laboratory handling should follow the safety data for the specific metal, powder or compound involved; hazards can differ substantially between bulk metal, fine powder and soluble salts.
Quick FAQ
Is lanthanum a rare-earth element? Yes. It is conventionally grouped with the lanthanides and rare-earth elements.
Why is lanthanum useful in lenses? Lanthanum-containing glass can achieve optical properties such as a high refractive index that are valuable in precision lens design.
Where is La on the periodic table? Lanthanum is element 57 in period 6. You can compare it with neighboring elements on our periodic table guide.
