Lanthanum (La): Electron Configuration, Properties and Uses
Lanthanum (La): Electron Configuration, Properties and Uses
Electron configuration [Xe] 6s2 5d1 · f-block, lanthanide series · period 6 · Ar 138.91
Lanthanum data
- Atomic number
- 57
- Relative atomic mass
- 138.91
- Group
- – (lanthanide series)
- Period
- 6
- Block
- f
- Category
- Lanthanide
- Electron configuration
- [Xe] 6s2 5d1
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1
- Electrons per shell
- 2, 8, 18, 18, 9, 2 (K L M N O P)
- Valence electrons
- 2 (in the outer shell)
- Electronegativity (Pauling)
- 1.1
- First ionisation energy
- 5.577 eV
- Atomic radius (van der Waals)
- 240 pm
- State at room temperature
- Solid
- Melting point
- 918 °C
- Boiling point
- 3464 °C
- Density
- 6.15 g/cm³
- Common oxidation states
- +3
- Discovered
- 1839
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 18 · O 9 · P 2
Orbital diagram (outer electrons)
About lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57. It belongs to the lanthanide series in period 6 (f-block), usually shown below the main table. The element was discovered in 1839. Lanthanum is a solid at room temperature, melting at 918 °C and boiling at 3464 °C.
Lanthanum electron configuration
The electron configuration of lanthanum is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1, or in short [Xe] 6s2 5d1. Its electrons occupy 6 shells: K = 2, L = 8, M = 18, N = 18, O = 9, P = 2. As a lanthanide, lanthanum fills the 4f subshell. Its outer 6s subshell holds 2 electrons; valence electrons for this series are not assigned by the usual group rule. This is an exception to the Aufbau rule: the usual filling order predicts [Xe] 6s2 4f1, but the 4f and 5d subshells are so close in energy that electrons occupy 5d. When it forms cations, electrons leave the outermost subshell first: La3+ = [Xe] (like xenon).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p6(36) → 5s2(38) → 4d10(48) → 5p6(54) → 6s2(56) → 5d1(57)
Uses of lanthanum
The main uses of lanthanum include high-refractive-index camera lenses, NiMH batteries and petroleum cracking catalysts. For research and analysis you can browse lanthanum compounds in the AMI Scientific catalogue.
Safety
As a solid metal, lanthanum is not especially hazardous. Fine powder can burn, and its compounds should be handled according to their SDS. Always read the safety data sheet (SDS) before working with a chemical.
Other lanthanides
Frequently asked questions
What is the electron configuration of lanthanum?
The electron configuration of lanthanum (La, atomic number 57) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1, or [Xe] 6s2 5d1 in short. By shell: 2, 8, 18, 18, 9, 2.
How many valence electrons does lanthanum have?
Lanthanum has 2 electrons in its outer shell. For lanthanides and actinides, valence electrons are not assigned by the usual group rule.
Which group and period is lanthanum in?
Lanthanum is in the lanthanide series, period 6, f-block.
What is the atomic mass of lanthanum?
The relative atomic mass of lanthanum is 138.91. Use it to calculate molar mass with the molar mass calculator.
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