CBSE Class 12 · 2001 · Foreign · d and f Block ElementsVery Short Answer

What is the difference between the electronic configurations of lanthanoids and actinoids?

Answer: Lanthanoids fill 4f (4f¹⁻¹⁴5d⁰⁻¹6s²); actinoids fill 5f (5f¹⁻¹⁴6d⁰⁻²7s²).

Solution

Lanthanoids: the added electrons enter the 4f subshell —

4 f^{1 - 14} 5 d^{0 - 1} 6 s^{2}

Actinoids: the added electrons enter the 5f subshell —

5 f^{1 - 14} 6 d^{0 - 2} 7 s^{2}

(5f, 6d and 7s are closer in energy, so actinoid configurations are more irregular.)

CBSE Class 12 Board · 2001 · Foreign · Subjective