057Lanthanide · Group 3 · Period 6

Lanthanum

Lanthanum (La) is element 57, a lanthanide in the f-block — group 3, period 6. It is a solid at room temperature with 6 electron shells (2, 8, 18, 18, 9, 2) and an atomic mass of 138.905477 u.

Atomic mass: 138.9 u
Phase · STP: solid
Melting: 1193 K · 920 °C
Boiling: 3737 K · 3464 °C
Electronegativity: 1.1
Density: 6.162 g/cm³

Photograph — Jurii, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons, source: https://images-of-elements.com/lanthanum.php

Identity

Atomic number: 57
Standard atomic weight: 138.9 u
Category: Lanthanide
Group: 3
Period: 6
Block: f-block
Oxidation states: +3

Physical properties

Melting point: 1193 K · 920 °C
Boiling point: 3737 K · 3464 °C
Density: 6.162 g/cm³
Molar heat capacity: 27.11 J/(mol·K)
Atomic radius: 240 pm
Electron affinity: 53 kJ/mol

Atomic structure

57protons

82neutrons

57electrons

2valence e⁻

Noble-gas notation: [Xe] 5d16s2
Full configuration: 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 5d1
Electrons per shell: 2, 8, 18, 18, 9, 2

Periodic trends

Where Lanthanum ranks across all 118 elements.

Electronegativity1.1

Ionization energy538.1 kJ/mol

Electron affinity53 kJ/mol

Density6.162 g/cm³

Atomic radius240 pm

Ionization energies

Energy to remove each successive electron (kJ/mol).

538.1

1.1k

1.9k

4.8k

5.9k

Successive ionization energies (kJ/mol, log scale).

Discovery

Discovered: 1839
Discovered by: Carl Gustaf Mosander
Named by: —
Appearance: silvery white