Question

The CORRECT electronic configuration of Cr is

• A. \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\)
• B. \(1s^2 2s^2 2p^6 3s^2 3p^6 3d^6\)
• C. \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^2 3d^4\)
• D. \(1s^2 2s^2 2p^6 3s^2 3p^3 3d^{10}\)

Hint:

For transition elements like Cr, the stability of half-filled or fully filled \(d\)-orbitals can lead to electron promotion from the \(s\)-orbital to the \(d\)-orbital. Always remember that stability of the \(d\)-block elements plays a role in their electronic configuration.

Answer 1

The Correct Option is A

The electronic configuration of Chromium (Cr) is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\). Chromium has an atomic number of 24, which means it has 24 electrons. According to the Aufbau principle and Hund’s rule, the 4s orbital is filled first before the 3d orbitals. However, Cr has an exceptional configuration where one electron from the 4s orbital is promoted to the 3d orbital, leading to a half-filled \(3d^5\) configuration, which is more stable than the expected \(3d^4 4s^2\) configuration.
Thus, the correct electronic configuration is \(1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^5\).