Name Lanthanum
Symbol La
Atomic Number 57
Atomic Mass 138.9 atomic mass units
Number of Protons 57
Number of Neutrons 82
Number of Electrons 57
Melting Point 920.0 C
Boiling Point 3469.0 C
Density 6.7 grams per cubic centimeter
Normal Phase Solid
Family Rare Earth Metals
Period 3
Cost $64 per gram



Origin of Name From the Greek word lanthanein, meaning to lie hidden
Date and Place of Discovery In 1839 in Stockholm, Sweden
Discovered by Carl Gustav Mosander
Common Compounds
Interesting facts
  • It is malleable, ductile, and can be cut with a knife.
  • It is the most reactive of the rare earth metals.
  • It reacts with carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur and the halogens.
  • When exposed to air, it will oxidize very quickly.
  • It reacts slowly to cold water, but rapidly with hot water.
  • It plays no biological role.
  • It is somewhat toxic and should be handled with care.
Common Uses
  • Carbon lighting
  • Infrared glass
  • Camera and telescope lenses
  • Improves the malleability of steel
  • Cast iron
  • Vacuum tubes
  • Arc welding
  • Substitute for radioactive thorium
  • Catalysts
  • Gas lantern mantles
  • Rock and ore age dating
  • Specialty glass
  • Water treatment
  • Tracer in molecular biology


Photo Courtesy of
Chemical Elements
Los Alamos National Labs
Web Elements

Lanthanum Atomic Structure Elements by Name Elements by Number Home