Question

# General electronic configurations of lanthanides are: A) $\left( {n - 2} \right){f^{1 - 14}}\left( {n - 1} \right){s^2}{p^6}{d^{0 - 1}}n{s^2}$ B) $\left( {n - 2} \right){f^{10 - 14}}\left( {n - 1} \right){d^{0 - 1}}n{s^2}$C) $\left( {n - 2} \right){f^{0 - 14}}\left( {n - 1} \right){d^{10}}n{s^2}$D) $\left( {n - 2} \right){f^{0 - 1}}\left( {n - 1} \right){f^{1 - 14}}n{s^2}$

Hint: Lanthanides (rare earth elements) contain fourteen elements from atomic numbers 58 to 71. Lanthanum is a d-block element whereas cerium to lutetium are f-block elements. In the periodic table, lanthanides are present in the sixth period and third group.

In lanthanides, the electrons enter the penultimate $\left( {n - 1} \right)d$ subshell and pre-penultimate $\left( {n - 2} \right)f$ subshell. The general electronic configuration of lanthanides is $\left( {n - 2} \right){f^{1 - 14}}\left( {n - 1} \right){d^{0 - 1}}n{s^2}$ . But the penultimate subshell also contains $\left( {n - 1} \right){s^2}$ and $\left( {n - 1} \right){p^6}$ electrons. Hence, the general electronic configuration of lanthanides will be $\left( {n - 2} \right){f^{1 - 14}}\left( {n - 1} \right){s^2}\left( {n - 1} \right){p^6}\left( {n - 1} \right){d^{0 - 1}}n{s^2}$.

It can also be written as $\left( {n - 2} \right){f^{1 - 14}}\left( {n - 1} \right){s^2}{p^6}{d^{0 - 1}}n{s^2}$.

The option B ) is an incorrect answer as $\left( {n - 2} \right){f^{10 - 14}}$ should be written as $\left( {n - 2} \right){f^{1 - 14}}$.

The option C ) is an incorrect answer as $\left( {n - 2} \right){f^{10 - 14}}$ should be written as $\left( {n - 2} \right){f^{1 - 14}}$.
Also $\left( {n - 1} \right){d^{10}}$ should be written as $\left( {n - 1} \right){d^{0 - 1}}$.

The option D ) is an incorrect answer as $\left( {n - 2} \right){f^{0 - 1}}$ should be written as $\left( {n - 2} \right){f^{1 - 14}}$.
Also $\left( {n - 1} \right){f^{1 - 14}}$ should be written as $\left( {n - 1} \right){d^{0 - 1}}$.

Hence, option A) is the correct answer.

Note: Lanthanides are called rare earth elements as they have very small occurrences (around $3 \times {10^{ - 4}}\%$ of earth’s crust). In ‘monazite sand’ lanthanides are available as lanthanide orthophosphates.