57LaLanthanum

Lanthanum is a chemical element with the symbol La and atomic number 57. It is a soft, ductile, silvery-white metal that tarnishes slowly when exposed to air. It is the eponym of the lanthanide series, a group of 15 similar elements between lanthanum and lutetium in the periodic table, of which lanthanum is the first and the prototype. Lanthanum is traditionally counted among the rare earth elements. Like most other rare earth elements, the usual oxidation state is +3, although some compounds are known with oxidation state +2. Lanthanum has no biological role in humans but is essential to some bacteria. It is not particularly toxic to humans but does show some antimicrobial activity.

Lanthanum usually occurs together with cerium and the other rare earth elements. Lanthanum was first found by the Swedish chemist Carl Gustaf Mosander in 1839 as an impurity in cerium nitrate – hence the name lanthanum, from the Ancient Greek λανθάνειν (lanthanein), meaning 'to lie hidden'. Although it is classified as a rare earth element, lanthanum is the 28th most abundant element in the Earth's crust, almost three times as abundant as lead. In minerals such as monazite and bastnäsite, lanthanum composes about a quarter of the lanthanide content. It is extracted from those minerals by a process of such complexity that pure lanthanum metal was not isolated until 1923.

Lanthanum compounds have numerous applications as catalysts, additives in glass, carbon arc lamps for studio lights and projectors, ignition elements in lighters and torches, electron cathodes, scintillators, gas tungsten arc welding electrodes, and other things. Lanthanum carbonate is used as a phosphate binder in cases of high levels of phosphate in the blood seen with kidney failure.

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Atomic properties

Standard atomic weight138.905 ±7·10-5
Atomic mass138.905 u

Atomic radii

Radius (empirical)187 pm
Covalent radius207 ±8 pm

Atomic shell

Electron configurationXe 5d1 6s2
Ionization energy(1st) 5.5769 eV
(2nd) 11.18496 eV
(3rd) 19.1773 eV
(4th) 49.95 eV
(5th) 61.6 eV
Shell model
Electrons
k-shell:2
l-shell:8
m-shell:18
n-shell:18
o-shell:9
p-shell:2

Physical properties

Phasesolid
Density6.17 g·cm−3 (293.1 K)
Molar volume2.239·10-5 m3·mol−1
Speed of sound2,475 m·s−1

Temperatures

Melting point1,193 K
Boiling point3,737 K
Liquid range2,544 K
Transition temperature6 K

Enthalpies

Melting enthalpy6.2 kJ·mol-1
Enthalpy of vaporization400 kJ·mol-1
Binding energy431 kJ·mol-1

Heat and conductivity

Thermal conductivity13 W·m-1·K-1
Expansion coefficient1.21·10-5 K-1

Hardnesses

Mohs hardness2.5
Brinell hardness363 NM·m-2
Vickers hardness491 NM·m-2

Elastic properties

Young’s modulus37 GPa
Shear modulus14 GPa
Bulk modulus28 GPa
Poisson’s ratio0.28

Electrical properties

Electrical conductivity1.63·106 S·m-1
Resistance6.15·10-7 Ωm

Magnetism

Magnetismparamagnetic
Magnetic susceptibility1.18·10-4 cm3·mol−1 (298 K)

Chemical properties

Basicityslightly basic
Oxidation state3
Standard potential-2.38 V (La3+ + 3e- → La)

Electronegativity

Pauling scale1.1
Allred-Rochow scale1.08
Nagle scale1.04
Pearson absolute negativity3.1 eV

Other properties

Natural occurrenceprimordial
Crystal structureDouble hexagonal close-packed
Goldschmidt Classificationlithophile
Superconductorwith transition tempperature (solid body, normal pressure)
Price/kg4.85 ±0.07 USD

Natural abundances

satellite_alt
Universe
2 ppb ≈ 2.01·1010 M☉
sunny
Sun
2 ppb ≈ 3.97·109 Mt
destruction
Meteorite
290 ppb ≈ 290 mg
public
Earth’s crust
34,000 ppb ≈ 941,000 Mt
water_drop
Oceans
0.0034 ppb ≈ 4.65 kt
waves
Flowing water
0.2 ppb ≈ 3.2 kt
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