A group of elements whose
electronic configurations display back filling
of the 4f-level. There is a maximum of
14 electrons in an f-orbital. The element
lanthanum itself has no f-electrons (La
[Xe]5d16s2) and is thus strictly not a lanthanoid,
but it is included by convention,
thus giving a closely related series of 15 elements.
Excluding lanthanum, the elements
all have 4fx6s2 configurations but
gadolinium and lutecium have an additional
5d1 electron.
The characteristic oxidation state is
M3+ and the great similarity in the size of
the ions leads to a very close similarity of
chemical properties and hence to great difficulties
of separation using conventional
methods. Chromatographic and solvent solventextraction
methods have been specially developed
for the lanthanoids.
The lanthanoid series consists of 14 elements (cerium to lutetium) and they are also called f-block metals,
as the valence shell of lanthanoids contains 4f orbitals. Lanthanoids are named after the element lanthanum
(La), which itself is a d-block metal. Nevertheless, because of its very similar chemical behaviour, lanthanum
is often also classified as a lanthanoid. The term rare earth metals describes the lanthanoid series together
with lanthanum (La), scandium (Sc) and yttrium (Y).
Mostly, lanthanoids are used in the production of batteries, lasers and other technological devices. Some
lanthanoids salts, such as the salts of lanthanum, cerium and gadolinium (highlighted in Figure 9.1), are
increasingly used in a clinical setting, for example, as a phosphate binder in the treatment of renal osteodystrophy
or as MRI (magnetic resonance imaging) contrast agents (CAs).
