Rare Earth Properties – Lanthanides and Actinides

When you look at the Periodic Table, there is a two-row block of elements located below the main body of the chart. These elements, plus lanthanum (element 57) and actinium (element 89), are known collectively as the rare earth elements or rare earth metals. Actually, they aren’t particularly rare, but prior to 1945, long and tedious processes were required to purify the metals from their oxides. Ion-exchange and solvent extraction processes are used today to quickly produce highly pure, low-cost rare earths, but the old name is still in use. The rare earth metals are found in group 3 of the periodic table, and the 6th (5d electronic configuration) and 7th (5f electronic configuration) periods. There are some arguments for starting the 3rd and 4th transition series with lutetium and lawrencium rather than lanthanum and actinium.

Rare Earth Properties - Lanthanides and Actinides

Rare Earth Properties – Lanthanides and Actinides

There are two blocks of rare earths, the lanthanide series, and the actinide series. Lanthanum and actinium are both located in group IIIB of the table. When you look at the periodic table, notice that the atomic numbers make a jump from lanthanum (57) to hafnium (72) and from actinium (89) to rutherfordium (104). If you skip down to the bottom of the table, you can follow the atomic numbers from lanthanum to cerium and from actinium to thorium, and then back up to the main body of the table. Some chemists exclude lanthanum and actinium from the rare earths, considering the lanthanides to start following lanthanum and the actinides to start following actinium. In a way, the rare earths are special transition metals, possessing many of the properties of these elements.

Rare Earth Properties periodic table

Rare Earth Properties periodic table

A rare-earth element or rare-earth metal, is one of a set of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides, as well as scandium and yttrium. Scandium and yttrium are considered rare-earth elements because they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties, but have different electronic and magnetic properties. Rarely, a broader definit.

Properties Of The Rare Earth Metals

As noted above, the rare-earth elements—especially the lanthanides—are quite similar. They occur together in nature, and their complete separations are difficult to achieve. However, there are some striking differences, especially in the physical properties of the pure metallic elements. For example, their melting points differ by nearly a factor of two, and the vapour pressures differ by a factor of more than one billion. These and other interesting facts are discussed below.

There are several different processes of preparing the individual rare-earth metals, depending upon the given metal’s melting and boiling points (see below Properties of the metals) and the required purity of the metal for a given application. For high-purity metals (99 percent or better), the calciothermic and electrolytic processes are used for the low-melting lanthanides (lanthanum, cerium, praseodymium, and neodymium), the calciothermic process for the high-melting metals (scandium, yttrium, gadolinium, terbium, dysprosium, holmium, erbium, and lutetium, and another process (the so-called lanthanothermic process) for high-vapour-pressure metals (samarium, europium, thulium, and ytterbium). All three methods are used to prepare commercial-grade metals (95–98 percent pure).

Common Properties of the Rare Earths

These common properties apply to both the lanthanides and actinides.
The rare earths are silver, silvery-white, or gray metals.
The metals have a high luster but tarnish readily in air.
The metals have high electrical conductivity.
The rare earths share many common properties. This makes them difficult to separate or even distinguish from each other.
There are very small differences in solubility and complex formation between the rare earths.
The rare earth metals naturally occur together in minerals (e.g., monazite is a mixed rare earth phosphate).
Rare earths are found with non-metals, usually in the 3+ oxidation state. There is little tendency to vary the valence. (Europium also has a valence of 2+ and cerium also a valence of 4+.)

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