Question

The electron configuration for chromium is $\left[Ar\right]4s^{1}3d^5$.
Select the best explanation for this irregular electron configuration.

• A. A half-filled d orbitals is slightly lower is energy than the $4s$, thus filling first.
• B. The $4s$ orbital is at a lower energy than the $3d$ orbital, thus filling first.
• C. Chromium is a transition metal and its electrons are loosely held.
• D. $d$ orbitals are dominant and shield electrons from orbitals close in energy.

Answer 1

The correct option is A A half-filled d orbitals is slightly lower is energy than the $4s$, thus filling first.

The half filled $d$ orbital is lower in energy than $4s$ orbital hence it provides more stability. Thus the irregular configuration is observed. Hence answer is option A.