Transition Metals vs Inner Transition Metals
The elements of the periodic table are arranged according to an ascending pattern depending on how the electrons are filled into atomic energy levels and their subshells. The characteristics of these elements show a direct correlation with the electron configuration. Therefore, regions of elements with similar properties can be identified and blocked for the sake of convenience. The first two columns in the periodic table contain elements where the final electron is being filled into a ‘s’ subshell, hence termed as ‘s-block’. The last six columns of an extended periodic table contain elements where the final electron is being filled into a ‘p’ subshell, hence termed ‘p-block’. Similarly columns from 3-12 contain elements where the last electron is being filled into a ‘d’ subshell, thus called the ‘d-block’. Finally, the extra element set that is often written as two separate rows at the bottom of the periodic table or sometimes written in between columns 2 and 3 as an extension is called the ‘f-block’ as their final electron is being filled into a ‘f’ subshell. The ‘d-block’ elements are also referred to as ‘Transition Metals’ and the ‘f-block’ elements are also called ‘Inner Transition Metals’.
These elements come to picture beginning from the 4th row and the term ‘transition’ was used because it extended the inner electronic shells making the stable ‘8 electron’ configuration to an ’18 electron’ configuration. As mentioned above, the elements in the d-block belong to this category which span from groups 3-12 in the periodic table and all the elements are metals, hence the name ‘transition metals’. The elements in the 4th row, groups 3-12, are collectively called first transition series, the 5th row as the second transition series, and so on. Elements in the first transition series include; Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn. Usually, transition metals are said to have unfilled d sub-shells hence elements such as Zn, Cd, and Hg, which are in the 12th column, tend to be excluded from the transition series.
Apart from consisting of all metals, the d-block elements possess several other characteristic properties that give it their identity. Most of the transition series metals compounds are coloured. This is due to the d-d electronic transitions; i.e. KMnO4 (purple), [Fe(CN)6]4- (blood red), CuSO4 (blue), K2CrO4 (yellow) etc. Another property is the exhibition of many oxidation states. Unlike the s-block and p-block elements, majority of the d-block elements have varying oxidation states; i.e. Mn (0 to +7). This quality has made the transition metals act as good catalysts in reactions. Furthermore, they show magnetic properties and essentially acts as paramagnets when having unpaired electrons.
Inner Transition Metals
As stated in the introduction, the elements of the f-block fall under this category. These elements are also called ‘rare earth metals’. This series is included after the 2nd column as the bottom two rows connecting to the d-block in an extended periodic table or as two separate rows at the bottom of the periodic table. The 1st row is called ‘Lanthanides’, and the 2nd row is called ‘Actinides’. Both lanthanides and actinides have similar chemistries, and their properties differ from all other elements due to the nature of the f orbitals. (Read the Difference Between Actinides and Lanthanides.) Electrons in these orbitals are buried inside the atom and are shielded by outer electrons and, as a result, the chemistry of these compounds is largely dependent on the size. Ex: La/Ce/Tb (lanthanides), Ac/U/Am (actinides).
What is the difference between Transition Metals and Inner Transition Metals?
• Transition metals consist of d-block elements whereas inner transition metals consist of f-block elements.
• Inner transition metals have low availability than transition metals and hence called ‘rare earth metals’.
• Transition metal chemistry is mainly due to varying oxidation numbers, whereas inner transition metal chemistry is mainly dependent on atomic size.
• Transition metals are generally used in redox reactions, but the usage of inner transitional metals for this purpose is rare.
Also, read the Difference Between Transition Metals and Metals