Discovered | Name | Characteristics | Uses

Lanthanum is a metal in Group IIIB and the 6th period. It has oxidation numbers of 0 and +3. Other elements of Group IIIB are scandium (Sc), yttrium (Y), and actinium (Ac).

In 1839 the Swedish chemist Carl Gustav Mosander - whom the great chemist Berzelius called "Father Moses" - discovered a new "earth" in an impure sample of cerium nitrate.

He named the new compound lanthana, which means "hidden". The "earth" is now known to be lanthanum oxide, La2O3. The pure metal was not isolated until 1923.

Lanthanum is the first element in the series of elements commonly called the "lanthanides" but also called the "rare earths". However, these elements are not nearly as rare in earth's crust as once thought (cerium, for example, is about half as abundant as chlorine).

The elements of Group IIIB are not as rare as once thought. Their abundances in the earth's crust are Sc, 25; Y, 31; and La, 35 ppm; this makes them about as abundant as cobalt.

Y and La are almost always associated with the rare earth elements (the lanthanides, which stretch from lanthanum to lutetium). Lanthanum is chiefly recovered from monazite, a metal phosphate where the metal can be Y, La, or a lanthanide.

Lanthanum is silvery white, malleable, ductile, and soft enough to be cut with a knife. All the metals of Group IIIB tarnish easily in air, and all burn readily to give, for example, La2O3. They all react with halogens at room temperature, and all reduce water to give the metal hydroxide and H2 gas. All react with acids to give the appropriate metal salt.

Although these elements - Sc, Y, and La - are the first in the transition metal series, their chemistry is somewhat atypical. In large part this is owing to the fact that they form only +3 ions. The variable oxidation numbers characteristic of transition metals are absent, and their simple salts are often colorless since they have no d electrons remaining.

When one talks about the uses of the lanthanides, it is rare that a pure metal or oxide has a specific use. Rather, since the chemistries of the elements are similar, thus making them difficult to separate, it is more usual that it is a mixture of rare earth compounds that has a practical use. For example, "misch metal", a mixture of various rare earth metals, is used in lighter flints, and rare earth oxides are also used in phosphors for television screens (LaMgAl11O19) and similar fluorescing devices.

One of the largest uses of rare earth compounds containing lanthanum is in the movie industry for studio lighting and projection. Lanthanum oxide also improves the resistance of glass to alkalis and is used in making special optical glass, and it is used in catalysts for petroleum "cracking".

Finally, there is great interest in lanthanum as a "hydrogen sponge". When exposed to H2, the metal absorbs the gas. H2 molecules break into H atoms, which fill small spaces (interstices) among the La atoms. When the H atoms are released from the metal, they recombine, with the evolution of the H-H bond energy. Thus, this has possibilities as an energy storage device.