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) \[\left( {n - 2} \right){f^{0 - 1}}\left( {n - 1} \right){f^{1 - 14}}n{s^2}\]

Answer 1

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.

Complete answer:
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.