Lanthanum

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MELTING POINT: 920°C
BOILING POINT: 3,469°C
DENSITY: 6.16 g/cm ³
MOST COMMON IONS: La ³⁺

Elemental lanthanum has a ground state (electronic configuration) of [Xe]5d6s ² . Naturally occurring lanthanum is a mixture of two stable isotopes , ¹³⁸ La and ¹³⁹ La. The element was discovered in 1839 by Carl Gustaf Mosander in the form of the lanthanum oxide, at that time called "lanthana." The name is derived from the Greek lanthanein ("to lie hidden"), as the element had been overlooked due to its similarity to the earlier discovered cerium.

Monazite and bastnasite are the principal lanthanum ores, in which lanthanum occurs together with other members of the rare earth elements or the lanthanides . It can be separated from the other rare earths by ion exchange or solvent extraction techniques. Lanthanum is a silver-white, malleable, and ductile metal . It is soft enough to be cut with a knife. The metal is rapidly oxidized when exposed to air. Cold water attacks lanthanum only slowly, but reaction with hot water is fast.

Lanthanum chemistry is dominated by the trivalent lanthanum(III) ion, La ³⁺ . This ion forms ionic bonds with ligands containing an oxygen or nitrogen donor atom. The ground state electronic configuration of La ³⁺ is [Xe]4f ⁰ . Due to the absence of unpaired 4f electrons, lanthanum(III) compounds are colorless, both in solution and in the solid state. Lanthanum(III) oxide is added to optical glass to increase its refractive index and alkali resistance. Lanthanum-nickel alloys are being used in the storage of hydrogen gas. Thulium(III)- doped lanthanum oxybromide (LaOBr:Tm ³⁺ ) is a blue-emitting phosphor used in x-ray intensifying screens.

SEE ALSO Cerium ; Dysprosium ; Erbium ; Europium ; Gadolinium ; Holmium ; Lanthanides ; Lutetium ; Neodymium ; Praseodymium ; Promethium ; Samarium ; Terbium ; Ytterbium .

Koen Binnemans

Bibliography

Cotton, Simon (1991). Lanthanides and Actinides. New York: Oxford University Press.

Kaltsoyannis, Nikolas, and Scott, Peter (1999). The f Elements. New York: Oxford University Press.