Lanthanum (La)

Lanthanum means "to lie hidden", because Mosander found it concealed inside what everyone had taken for pure cerium — a fair description of the whole rare-earth story, in which one "element" after another turned out to be several. A Toyota Prius battery pack of the nickel-metal hydride generation contained on the order of 10 kg of lanthanum. Its electron configuration is anomalous: [Xe] 6s² 5d¹ with no 4f electron at all, which is exactly why it is arguable that lanthanum, not lutetium, belongs in group 3.

Properties

Atomic number

57

Symbol

La

Standard atomic weight

138.91 u

Category

Lanthanide

Period

6

Block

d-block

Electron configuration

[Xe] 6s² 5d¹

Electrons per shell

2, 8, 18, 18, 9, 2

Melting point

1,191 K — 917.9 °C — 1684.1 °F

Boiling point

3,737 K — 3463.8 °C — 6266.9 °F

Density

6.15 g/cm³

Electronegativity

1.1 (Pauling)

Oxidation states

+3

Discovered

1839 by Carl Gustaf Mosander

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 5d¹

Noble gas shorthand

[Xe] 6s² 5d¹

Shells

K: 2 · L: 8 · M: 18 · N: 18 · O: 9 · P: 2

What it is used for

• Nickel-metal hydride battery electrodes, including in hybrid cars
• Fluid catalytic cracking catalysts in oil refineries
• High-refractive-index camera and telescope lenses
• Carbon arc lamps for studio and projector lighting
• Mischmetal in lighter flints, alloyed with cerium

Anomalous electron configuration: [Xe] 6s² 5d¹ rather than the predicted 6s² 4f¹ — the first lanthanide has no f electrons. Filed in the d-block for that reason, though tables that place lutetium in group 3 put lanthanum in the f-block instead.

Neighbours in the table