Question

Question #480a7

Answer 1

Because a half-filled subshell is more stable than an almost half-filled subshell.

Explanation:

Although different people prefer to write their electron configurations differently, I prefer to organize the orbitals based on the order in which they are filled.

V: [Ar] `4s^2` `3d^3`
Cr: [Ar] `4s^1` `3d^5`

Instead of chromium having a `3d^4` subshell, it was more stable for a 4s electron to jump up a subshell. This leaves chromium with a half-filled 4s subshell and a half-filled 3d subshell.

Half-filled subshells are more stable because of their symmetry. Based on Hund's rule of maximum multiplicity, electrons will fill each orbital with one electron before pairing electrons. A half-filled subshell will have every orbital filled with exactly one electron, making it more stable.