Question

Give the electronic configuration of Ce⁴⁺ and Co²⁺.

Hint:

For transition metals (d-block) and lanthanides (f-block), always remember to empty the outermost s orbital first, even if the d or f orbitals were filled last according to the Aufbau principle.

Answer 1

Concept: The electronic configuration of an ion is determined by starting with the ground-state configuration of the neutral atom and removing electrons. Electrons are always removed first from the orbital with the highest principal quantum number (n).
1. Cerium (Ce⁴⁺)
Ce = [Xe] 4f¹ 5d¹ 6s² Ce⁴⁺ = [Xe] or [Kr] 4d¹⁰ 5s² 5p⁶ As a result, Ce⁴⁺ achieves a stable noble gas configuration (Xenon).
2. Cobalt (Co²⁺)
Co = [Ar] 3d⁷ 4s² Co²⁺ = [Ar] 3d⁷