(So named (Greek lanthanein, "to be hidden") in 1839 by Karl Mosander, its discoverer, because it had been previously undetected in the mineral cerite) A soft, ductile, malleable, silvery chemical element, one of the rare-earth metals and the first member of the lanthanide series.

Symbol: La
Atomic number: 57
Atomic weight: 138.9055
Density (at room temperature and pressure): 6.15 g/cc
Melting point: 920°C
Boiling point: 3,464°C
Valence: +3
Ground state electron configuration: [Xe]5d16s2

Lanthanum
Symbol: La
Atomic Number: 57
Atomic Weight: 138.9055
Boiling Point: 3737 K
Melting Point: 1191 K
Density at 300K: 6.15 g/cm3
Covalent radius: 1.25
Atomic radius: 2.74
Atomic volume: 22.5 cm3/mol
First ionization potental: 5.58 V
Specific heat capacity: 0.19 J g-1 K-1
Thermal conductivity: 13.5 W m-1 K-1
Electrical conductivity: 1.9*106Ω-1 m-1
Heat of fusion: 11.3 kJ/mol
Heat of vaporization: 399.57 kJ/mol
Electronegativity: 1.10 (Pauling's)

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Lan"tha*num (?), n. [NL., fr. Gr. to lie hid, to be concealed.] Chem.

A rare element of the group of the earth metals, allied to aluminium. It occurs in certain rare minerals, as cerite, gadolinite, orthite, etc., and was so named from the difficulty of separating it from cerium, didymium, and other rare elements with which it is usually associated. Atomic weight 138.5. Symbol La.

[Formerly written also lanthanium.]

 

© Webster 1913.

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