Lanthanum
[Xe] 5d¹ 6s² · 2 · 8 · 18 · 18 · 9 · 2
The first of the lanthanides and the element that named the family. The name means hidden: lanthanum lay concealed inside cerium for almost forty years before Mosander found it.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
Drag to rotate, scroll to zoom
Atomic properties
- Atomic number
- 57
- Atomic mass
- 138.905 а.е.м.
- Electron configuration
- [Xe] 5d¹ 6s²
- Electrons per shell
- 2 · 8 · 18 · 18 · 9 · 2
- Block
- d-block
- Group
- no data
- Period
- 6
- Electronegativity (Pauling)
- 1.1
- Electronegativity (Allen)
- 1.09
- Atomic radius
- 240 pm
- Covalent radius
- 207 pm
- Van der Waals radius
- 240 pm
- Ionisation energy 1
- 538.1 kJ/mol
- Ionisation energy 2
- 1 067 kJ/mol
- Ionisation energy 3
- 1 850.3 kJ/mol
- Ionisation energy 4
- 4 819 kJ/mol
- Ionisation energy 5
- 5 940 kJ/mol
- Electron affinity
- 48 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +1, +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 6.162 g/cm³
- Melting point
- 1 193 K · 919.9 °C
- Boiling point
- 3 737 K · 3 463.9 °C
- Speed of sound
- 2 475 m/s
Thermal properties
- Heat of fusion
- 6.2 kJ/mol
- Heat of vaporisation
- 400 kJ/mol
- Specific heat capacity
- 0.195 J/(g·K)
- Thermal conductivity
- 13.4 W/(m·K)
Mechanical properties
- Young's modulus
- 36.6 GPa
- Shear modulus
- 14.3 GPa
- Bulk modulus
- 27.9 GPa
- Poisson ratio
- 0.28
- Mohs hardness
- 2.5
- Brinell hardness
- 363 MPa
Electrical and magnetic properties
- Electrical resistivity
- 615 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- 4.88 K
Crystal structure
- Crystal structure
- hexagonal close-packed (hcp)
- Lattice constants
- a = 377.2 pm · c = 1 214.4 pm
Abundance
- In the crust
- 39 mg/kg
- In the ocean
- 3.4·10⁻⁶ mg/L
- In the universe
- 2 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 138La | 0.089 % | 101.4 Gyr | ЭЗ |
| 139La | 99.911 % | stable | — |
Lanthanum-138 is 0.09 % of natural lanthanum and radioactive with a 10¹¹-year half-life; lanthanum-barium-cerium dating is used in geochronology.
Discovery
- Year of discovery
- 1839
- Discovered by
- Carl Gustaf Mosander
- Where
- Sweden
- Origin of the name
- from Greek lanthanein (to lie hidden): it hid inside cerium
History
Carl Mosander showed in 1839 that cerium, discovered thirty-six years earlier, held a new element as an impurity. He named it from the Greek for to lie hidden — and over the following decades a dozen more elements came out of the same earths.
Where it occurs
39 mg/kg of the crust — more common than lead. The main minerals are bastnäsite and monazite.
How it is produced
By solvent extraction of rare-earth concentrates, then electrolysis of the molten chloride or metallothermic reduction.
Role in living things
No role in higher organisms, but in 2014 a bacterium was found whose enzyme specifically requires a lanthanide — the first known case.
Safety
Of low toxicity. Lanthanum carbonate is a prescribed phosphate binder for patients with kidney failure.
Uses
- Nickel-metal hydride batteries: the alloy LaNi₅ stores hydrogen
- Petroleum cracking catalysts — the largest use by volume
- High-refractive-index optical glass for camera lenses
- Mischmetal: a lanthanum-cerium alloy in lighter flints
Curiosities
- Lanthanum's name means to hide — and the whole lanthanide family is named after the one that hid best.
- First-generation hybrid cars carried ten kilograms or more of lanthanum in their battery packs.
- Lanthanum was found as an impurity in cerium, and cerium later yielded nine more elements.
- The rare earths are misnamed: cerium is commoner than copper and lanthanum commoner than lead.