General electronic configuration of lanthanides is
A
$(n-2)f^{1-14}\,(n-1)s^2p^6d^{0-1}\,ns^2$
B
$(n-2)f^{10-14}\,(n-1)d^{0-1}\,ns^2$
C
$(n-2)f^{0-14}\,(n-1)d^{10}\,ns^2$
D
$(n-2)d^{0-1}\,(n-1)f^{1-14}\,ns^2$
The answer is A.
Solution
Lanthanoids are in the sixth period (n = 6). The differentiating electron enters the 4f subshell, i.e. the $(n-2)f$ subshell. Their general configuration is $[Xe]\,4f^{1-14}\,5d^{0-1}\,6s^2$. In general form: $(n-2)f^{1-14}\,(n-1)s^2p^6d^{0-1}\,ns^2$, where the filled $5s^2\,5p^6$ of the $(n-1)$ shell is written out. The other forms have the wrong range of f electrons, a full $d^{10}$, or the shells in the wrong order. So the general configuration is $(n-2)f^{1-14}\,(n-1)s^2p^6d^{0-1}\,ns^2$.
ConceptGeneral configuration of f-block
Electronic configuration of lanthanoids in past papers
2 questions from this chapter have appeared across 2 exam years.
