Lanthanum: the essentials

Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. It is one of the most reactive of the rare-earth metals. It oxidises rapidly when exposed to air. Cold water attacks lanthanum slowly, and hot water attacks it much more rapidly. The metal reacts directly with elemental carbon, nitrogen, boron, selenium, silicon, phosphorus, sulphur, and with halogens. It is a component of, misch metal (used for making lighter flints).

Table: basic information about and classifications of lanthanum.

Lanthanum: historical information

Lanthanum was discovered by Carl Gustaf Mosander at 1839 in Sweden. Origin of name: from the Greek word "lanthanein" meaning "to lie hidden".

Carl Gustav Mosander recognized the element lanthanum in impure cerium nitrate in 1839. His extraction resulted in the oxide lanthana (La2O3). A number of other lanthanides (rare-earths) were later discovered by identification of the impurities in yttrium and cerium compounds.

Lanthanum: physical properties

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Lanthanum: orbital properties

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Isolation

Isolation: lanthanum metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to separate it from as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.

For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.

Pure lanthanum is available through the reduction of LaF3 with calcium metal.

2LaF3 + 3Ca → 2La + 3CaF2

This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.

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lanthanum atomic number