Lanthanum

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Lanthanum is a chemical element with the symbol La and atomic number 57. Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is a lanthanide. Found in some rare-earth minerals, usually in combination with cerium and other rare earth elements. Lanthanum is malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulfur, and with halogens. It oxidizes rapidly when exposed to air. Cold water attacks lanthanum slowly, while hot water attacks it much more rapidly.

 

General
Name, Symbol, Number lanthanum, La, 57
Chemical series lanthanides
Group, Period, Block 3, 6, f
Appearance silvery white
Standard atomic weight 138.90547(7) g·mol-1
Electrons per shell 2, 8, 18, 18, 9, 2
Physical properties
Phase solid
Density (near r.t.) 6.162 g·cm−3
Liquid density at m.p. 5.94 g·cm−3
Melting point 1193K
(920°C, 1688°F)
Boiling point 3737K
(3464°C, 6267°F)
Heat of fusion 6.20 kJ·mol-1
Heat of vaporization 402.1 kJ·mol-1
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
Crystal structure hexagonal
Oxidation states 3
(strongly basic oxide)
Electronegativity 1.10 (Pauling scale)
Ionization energies
(more)
1st: 538.1 kJ·mol-1
2nd: 1067 kJ·mol-1
3rd: 1850.3 kJ·mol-1
Atomic radius 195 pm
Covalent radius 169 pm
Miscellaneous
Magnetic ordering  ?
Electrical resistivity (r.t.) (α, poly) 615 nΩ·m
Thermal conductivity (300K) 13.4 W·m-1·K-1
Thermal expansion (r.t.) (α, poly)
12.1 µm/(m·K)
Speed of sound (thin rod) (20 °C) 2475 m/s
Young's modulus (α form) 36.6 GPa
Shear modulus (α form) 14.3 GPa
Bulk modulus (α form) 27.9 GPa
Poisson ratio (α form) 0.280
Mohs hardness 2.5
Vickers hardness 491 MPa
Brinell hardness 363 MPa
CAS registry number 7439-91-0

 

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