ElementsWhat is lanthanum?
Lanthanum is a soft, silvery-white metal and the first of the lanthanides, a row of elements often called rare earths.
What is lanthanum used for?
Camera and telescope lenses, hybrid car batteries, catalysts in oil refining, and lighter flints.
Where the name comes from
From the Greek word lanthanein, to lie hidden.
Key facts
- Symbol
- La
- Atomic number
- 57
- Atomic mass
- 138.9055 u
- Family
- Lanthanide
- Period
- 6
- Group
- none (f-block)
- Block
- f
- State at room temperature
- Solid
- Melting point
- 917.9 °C (1,191 K, 1,684 °F)
- Boiling point
- 3,464 °C (3,737 K, 6,267 °F)
- Density
- 6.15 g/cm³
- Electrons per shell
- 2, 8, 18, 18, 9, 2
- Electron configuration
- [Xe]6s2 5d1
- Common oxidation states
- +3
- Electronegativity (Pauling)
- 1.1
- First ionisation energy
- 5.577 eV
- Electron affinity
- 0.5 eV
- Atomic radius (van der Waals)
- 240 pm
- Discovered
- 1839
Place in the periodic table
Lanthanum is element number 57. It sits in period 6 (row 6) of the periodic table, in the separate row of lanthanides drawn below the main table, and belongs to the f-block. Just before it comes barium (56), and just after it comes cerium (58).
Family: Lanthanides.
Physical properties
At room temperature lanthanum is a solid. It melts at 917.9 °C and boils at 3,464 °C, so it stays liquid over a range of 2,546 degrees. Its density is 6.15 grams per cubic centimetre, so a one-litre block would weigh about 6.15 kilograms. By density it ranks 57th among the 96 elements with a measured value.
Inside the atom
An atom of lanthanum has 57 protons in its nucleus and, when neutral, 57 electrons around it. The electrons are arranged in 6 shells: 2, 8, 18, 18, 9, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Xe]6s2 5d1.
Its electronegativity on the Pauling scale is 1.1. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 5.577 electronvolts (about 538 kilojoules per mole). One mole of lanthanum weighs 138.9055 grams, so a single gram contains about 4.34 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains lanthanum with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.