Question

Write observed electronic configuration of chromium (Z = 24).

Hint:

Remember both Chromium (\(Z=24\)) and Copper (\(Z=29\)) follow this trend to achieve half-filled (\(d^5\)) and fully-filled (\(d^{10}\)) stability respectively.

Answer 1

Step 1: Understanding the Concept:
According to the Aufbau principle, the expected configuration would be \( [Ar] \, 3d^4 \, 4s^2 \). However, certain elements show anomalies to gain extra stability.
Step 2: Detailed Explanation:
Chromium (\(Z=24\)) exhibits an exceptional configuration. One electron from the \(4s\) orbital shifts to the \(3d\) orbital.
This results in a configuration of \( [Ar] \, 3d^5 \, 4s^1 \).
This is because:
1. Symmetry: Half-filled subshells (\(d^5\)) are more symmetrical and therefore more stable.
2. Exchange Energy: A half-filled \(d\) subshell allows for maximum exchange of electron positions, leading to higher exchange energy and lower overall energy of the atom.
Step 3: Final Answer:
The observed electronic configuration of \(Cr\) is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\).