Question

Why chromium has electronic configuration 3d5 4s1 and not 3d4 4s2?

Answer 1

Explanation:

Half filled d5 & full filled d10 orbitals are more stable so, E.C of cr(24) is writen as [Ar]3d5 4s1 instead of [Ar]3d4 4s2 because half filled E.C is more stable.

Answer 2

The electronic configuration of chromium, $3d^{5} 4s^{1}$ , imparts stability to the element.

• The filling of electrons is governed by the Aufbau Principle.
• Aufbau principle states that the filling of higher energy orbitals occurs only after the lower energy orbitals are filled.
• So according to the Aufbau principle, chromium must possess an electronic configuration, $4s^{2}3d^{4}$(since 4s orbitals have lower energy than 3d orbitals).
• Half filled orbitals have greater stability. In the case of $3d^{5} 4s^{1}$, the 3d orbitals being half-filled, imparts more stability. So Chromium has an electronic configuration,$3d^{5} 4s^{1}$, not $3d^{4} 4s^{2}$.