Periodic Table


Atomic number: 57
Atomic weight: 138.9055
Symbol: La
Group number: 3
Electronic configuration: [Xe].5d1.6s2


Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. It oxidises rapidly when exposed to air. Cold water attacks lanthanum slowly, and hot water attacks it much more rapidly. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulphur, and with halogens. It is a component of, misch metal (used for making lighter flints).

General information

Discoveror: Carl Gustaf Mosander
Date discovered: 1839
Discovered at: Sweden
Meaning of name: From the Greek word "lanthanein" meaning "to lie hidden"

Physical data

Standard state: solid at 298 K
Colour: silvery white
Density of solid at ambient temperature/kg m-3: 6146
Molar volume/cm3: 22.39

Radii /pm

Atomic: no data
Covalent (single bond):
Pauling radius for the ion [La]-: no data

Valence shell orbital radius maxima (Rmax)
orbital s p d f
radius220.1no data115.0no data


Both values are quoted on the Pauling scale.

Pauling: 1.10
Allred Rochow: 1.08

Crystal Structure

structure: hcp (hexagonal close-packed)

The following CrystalMaker image represents the solid state structure. For most elements, the most stable allotrope is illustrated. Try WebElements version 2 for interactive virtual reality and CHIME images.


Temperatures (/K)

melting point: 1193
boiling point: 3743

Enthalpies /kJ mol-1

fusion: 8.5
vaporization: 401

single bond enthalpies:
La-F La-Cl La-Br La-I La-La
no data no data no data no data 247

Ionization enthalpies /kJ mol-1

Number Enthalpy


This section gives some data for naturally occurring isotopes.
Nominal mass Accurate mass % natural abundance
138La137.907105 (6)0.0902 (2)
139La138.906347 (5)99.9098 (2)

Further Information

Copyright 1997 Mark Winter
Department of Chemistry at the University of Sheffield, Sheffield S3 7HF, England.

The current version of this document is at http://www.shef.ac.uk/~chem/web-elements-I/La.html