Chemical element · reference page

57La

Lanthanum

Lanthanum is element 57 (La), located in period 6, group — and the f block. At room temperature its reference phase is solid. Its electron configuration is [Xe] 5d16s2.

Atomic number57

Standard atomic weight138.90547(7)

Group—

Period6

Blockf

Electron configuration[Xe] 5d16s2

Electronic structure

What controls its chemistry

The lanthanides are characterised by filling of the 4f subshell. Their chemistry is often dominated by the +3 oxidation state, while partially filled f orbitals give many members useful magnetic and optical properties.

Because the 4f electrons are relatively shielded, neighbouring lanthanides have very similar chemical behaviour. Separating them from one another is therefore much harder than separating elements from different main groups.

Chemical forms

Compounds, ions and materials

Lanthanides are commonly encountered as +3 ions in oxides, halides and coordination compounds. Their compounds often have closely related chemistry, while differences in f-electron structure create distinctive magnetic and luminescent behaviour.

Physical behaviour

State and phase changes

The reference phase at room temperature is solid. The listed density is 6.162 g/cm³. The melting point is 1 192 K (918.9 °C). The boiling point is 3 737 K (3 464 °C). Pressure, purity and crystal structure can shift measured physical properties.

Occurrence and applications

Where lanthanum is found and used

In practice, lanthanum is encountered in optical lenses, batteries and catalysts.

In practice

Examples of real uses

Optical lenses

Lanthanum is used in specialised glasses or optical materials to tune refractive index and dispersion.

Batteries

Lanthanum is used in selected battery chemistries, electrode materials or electrolytes. The exact role depends on the compound and cell design.

Catalysts

Lanthanum is used to accelerate chemical reactions without being consumed in the overall reaction.

Periodic position

What its neighbours tell us

Lanthanum is in period 6. In the f-block sequence shown here, it appears between barium and cerium. This sequence allows a direct comparison with the neighbouring f-block elements.

Reference data

Physical and atomic properties

Classificationlanthanide

Phase at room temperatureSolid

Electron shells2 · 8 · 18 · 18 · 9 · 2

Density6.162 g/cm³

Melting point1 192 K (918.9 °C)

Boiling point3 737 K (3 464 °C)

Pauling electronegativity1.1

First ionisation energy538.1 kJ/mol

Electron affinity53 kJ/mol

Values describe the element or neutral atom where applicable. Physical data can depend on allotrope, pressure and measurement conditions.

History

Discovery and identification

The discovery of lanthanum is associated with Carl Gustaf Mosander. Recognition of the element, isolation of a pure sample and assignment of its modern atomic number did not necessarily occur at the same time.

Isotopes and atomic weight

How isotope composition changes the numbers

The standard atomic weight is 138.90547(7). This value refers to the isotopic composition of natural terrestrial material, not to the mass of one specific atom.

Lanthanum has at least one stable isotope. Different isotopes have the same number of protons and therefore the same element identity, but different neutron numbers and atomic masses.

Safety

Handling and exposure

The hazards associated with lanthanum depend on chemical form, dose and route of exposure. Pure lanthanum, its ions and its compounds can have very different biological and environmental effects, so safety data should be checked for the actual substance being handled.