What is inner transition elements? what is lanthanoid series?

·         The f block elements are those which have partly filled f subshells of the third to the outermost (antepenultimate),
·         (n-2)th energy shells in their elementary or ionic state.
·         These elements are also called inner transition elements and are divided into two series.
·         (i)  The Lanthanoid series,
·         (ii) The Actinoid series
·         In Lanthanoids, it is the 4f subshell which is being successively filled while in actinoids, it is the 5f subshell which is being successively filled.
THE LANTHANOID SERIES:
·         Lanthanum (Z=57) and the next fourteen elements (Z= 58-71) which follow it are called Lanthanoids or l lanthanum lanthanones.
·         These fifteen elements closely resemble one another and form a distinct group with lanthanum as the prototype; hence the name lanthanoids or lanthanones.
·         The reason why they resemble lanthanum so closely lies in their electronic configurations.
·         The configuration of lanthanum is [Xe] 5d¹6s².
·         In the succeeding fourteen elements, 14 electrons are successively added to the empty 4f subshell of the lanthanum configuration.
·         Thus, while in cerium the element immediately following lanthanum, one 4f electron is added to the lanthanum configuration.
·         Hence, the last element of the series, fourteen 4f electrons is added to the lanthanum configuration.
        Hence, the configuration of cerium and lutetium are [Xe] 4f¹5d¹6s² and [Xe] 4f¹⁴5d¹6s² respectively.