Lanthanum (La)

Lanthanum is a chemical element with symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air and is soft enough to be cut with a knife.

Atomic Number

57

Atomic Mass

138.91 u

Category

lanthanide

Phase

solid

Density

6.162 g/cm³

Electron Shells

2, 8, 18, 18, 9, 2

Atomic Structure

Protons: 57 • Electrons: 57 • Neutrons: Varies by isotope

Electron Configuration: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 5d¹

Discovery

1839 • Carl Gustaf Mosander