The correct ground state electronic configuration of chromium atom is
- A.
- B.
- C.
- D.
Show answer and solution
Correct option: A
Solution
Wait — the official answer listed as option 1 is [Ar] 3d³ 4s¹, but the well-known correct configuration of Cr is [Ar] 3d⁵ 4s¹. Option 4 is [Ar] 4d⁵ 4s¹ (wrong subshell). None of the options perfectly matches, but the intended correct answer is clearly the one showing the half-filled 3d stability, which corresponds to [Ar] 3d⁵ 4s¹ — this must be a typo in option 1 (3d³ should be 3d⁵).
Chromium (Z = 24) adopts [Ar] 3d⁵ 4s¹ instead of the expected [Ar] 3d⁴ 4s² because a half-filled 3d subshell (3d⁵) is extra stable due to exchange energy — electrons in singly occupied orbitals of the same subshell maximize parallel spins, lowering the overall energy. This stabilization is large enough to promote one electron from 4s to 3d, giving six unpaired electrons and a lower total energy than the 3d⁴ 4s² arrangement.
Chromium (Z = 24) adopts [Ar] 3d⁵ 4s¹ instead of the expected [Ar] 3d⁴ 4s² because a half-filled 3d subshell (3d⁵) is extra stable due to exchange energy — electrons in singly occupied orbitals of the same subshell maximize parallel spins, lowering the overall energy. This stabilization is large enough to promote one electron from 4s to 3d, giving six unpaired electrons and a lower total energy than the 3d⁴ 4s² arrangement.
[1989]