Lanthanum

Chemical element, symbol La and atomic number 57 / From Wikipedia, the free encyclopedia

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Lanthanum is a chemical element; it has 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.

Quick facts: Lanthanum, Pronunciation, Appearance, Standar...
Lanthanum, 57La
Lanthanum-2.jpg
Lanthanum
Pronunciation/ˈlænθənəm/ (LAN-thə-nəm)
Appearancesilvery white
Standard atomic weight Ar°(La)
Lanthanum in the periodic table


La

Ac
bariumlanthanumcerium
Atomic number (Z)57
Groupf-block groups (no number)
Periodperiod 6
Block  f-block
Electron configuration[Xe] 5d1 6s2
Electrons per shell2, 8, 18, 18, 9, 2
Physical properties
Phase at STPsolid
Melting point1193 K (920 °C, 1688 °F)
Boiling point3737 K (3464 °C, 6267 °F)
Density (near r.t.)6.162 g/cm3
when liquid (at m.p.)5.94 g/cm3
Heat of fusion6.20 kJ/mol
Heat of vaporization400 kJ/mol
Molar heat capacity27.11 J/(mol·K)
Vapor pressure (extrapolated)
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 2005 2208 2458 2772 3178 3726
Atomic properties
Oxidation states0,[3] +1,[4] +2, +3 (a strongly basic oxide)
ElectronegativityPauling scale: 1.10
Ionization energies
  • 1st: 538.1 kJ/mol
  • 2nd: 1067 kJ/mol
  • 3rd: 1850.3 kJ/mol
Atomic radiusempirical: 187 pm
Covalent radius207±8 pm
Color lines in a spectral range
Spectral lines of lanthanum
Other properties
Natural occurrenceprimordial
Crystal structure double hexagonal close-packed (dhcp)
Double hexagonal close packed crystal structure for lanthanum
Thermal expansionα, poly: 12.1 µm/(m⋅K) (at r.t.)
Thermal conductivity13.4 W/(m⋅K)
Electrical resistivityα, poly: 615 nΩ⋅m (at r.t.)
Magnetic orderingparamagnetic[5]
Molar magnetic susceptibility+118.0×10−6 cm3/mol (298 K)[6]
Young's modulusα form: 36.6 GPa
Shear modulusα form: 14.3 GPa
Bulk modulusα form: 27.9 GPa
Speed of sound thin rod2475 m/s (at 20 °C)
Poisson ratioα form: 0.280
Mohs hardness2.5
Vickers hardness360–1750 MPa
Brinell hardness350–400 MPa
CAS Number7439-91-0
History
DiscoveryCarl Gustaf Mosander (1838)
Isotopes of lanthanum
Main isotopes[7] Decay
abun­dance half-life (t1/2) mode pro­duct
137La synth 6×104 y ε 137Ba
138La 0.089% 1.05×1011 y ε 138Ba
β 138Ce
139La 99.911% stable
Symbol_category_class.svg Category: Lanthanum
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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.[8] 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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