The inner transition element occupies a position in between the elements lanthanum (Z=57) and hafnium (Z=72), and also between actinium (Z=89) and rutherfordium (Z=104).  Elements from 58-71, follow lanthanide series are known as the lanthanides, and elements from 90-103, follow the actinium series, are known as the actinides.  There is mainly some doubts as to whether lanthanum and actinium should be considered as part of the transition metal of group 3B, with the elements following them as being the lanthanides and actinides respectively, or whether lanthanum and actinium might be considered the first elements of the lanthanides and actinides, with lutetium and lawrencium being a part of Group 3B.  The orderly arrangement shown above moves traditionally, but there seems to be a growing trend in favour of the previous scheme.

What are Inner Transition Elements?

The periodic table is divided into four distinct blocks, s-block, p-block, d-block and f-block. S-block and p-block elements are known as the representative elements. D-block elements are known as the transition elements. F-block elements are referred to as the inner transition elements or inner transition metals. Inner transition metals are generally placed at the bottom of the periodic table. These elements were sometimes also known as the rare earth elements or rare earth metals because of their extremely low natural occurrence. They comprise elements from 57-71 (these are known as lanthanides) and from 89-103 (these are known as the actinides). The lanthanides are quite similar. The actinides are all radioactive. Lanthanides are placed in period 6, whereas actinides are placed in period 7.

In these elements, although the outermost d and f subshells are placed close together in energy, this leads to some irregularities in the electronic structure. These irregularities in turn might lead to some uncertainty about where to place the elements. Lanthanum and actinium possess no electrons in their f subshells, and they are best fitted with the elements of group 3. Cerium and thorium also do not possess any f electrons but are still considered as a part of the inner transition element series.  

Properties of Inner Transition Metals

Here are some of the properties of inner transition metals:

• The third last shell of inner transition elements is generally filled with electrons.
• These elements also form compounds that possess profound catalytic activities.
• The atomic radii, for both lanthanides and actinides, keep on decreasing along with the series.
• In general, actinides are radioactive by nature.
• Similar to the transition metals, inner transition elements are coloured ions as well.
• Elements of this level basically show variable valencies.
• They possess metallic properties as well, resulting to be good conductors of heat and electricity.

Applications of Inner Transition Elements

Below given is a detailed list of where and how these inner transition elements are put into usage:

• These elements are generally utilized in making nuclear weapons. One of the main instances of the same is Uranium, which is highly reactive as it has naturally occurring isotopes that are unstable.
• Lanthanides are also mainly utilized to produce lasers.
• Majority of the inner transition metals help in the generation of nuclear power.
• These elements also possess several medicinal uses, like destroying specific targeted cells in the body. One such case is cancerous cells.
• Inner transition metals also help in making robust magnets.

Examples of Inner Transition Elements

The period 6 inner transition metals i.e.  (lanthanides) includes cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium, ytterbium (Yb), and lutetium (Lu).  The period 7 inner transition metals (i.e. actinides) includes thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr).

Conclusion

The inner transition elements are sometimes also known as the f-block elements, because in this region the f-orbitals are being filled in. The lanthanides (except for the synthetic element promethium), together with scandium (Sc) and yttrium (Y) are sometimes remarked as “rare earth elements” or “rare earth metals” (or just “rare earths”).  This term is not used  anymore, this is because of the ambiguity of which elements “should” be included in this category, and also because the majority of these “rare” elements are not especially rare.  Cerium is the 25th most abundant element in the Earth’s crust, and also the least abundant of the naturally-occurring lanthanides, lutetium, the 60th most abundant element, is even more common than either silver or gold.