Question

Electronic configuration of chromium is:

• A. [Ar] $3d^4\,4s^1$
• B. [Ar] $3d^4\,4s^2$
• C. [Ar] $3d^5\,4s^1$
• D. [Ar] $3d^5\,4s^2$

Hint:

Remember key exceptions in electronic configuration: Cr = [Ar] $3d^5\,4s^1$ Cu = [Ar] $3d^{10}\,4s^1$ They occur due to extra stability of half-filled and fully filled $d$ subshells.

Answer 1

The Correct Option is C

The question asks for the electronic configuration of chromium. Let's analyze why the correct configuration is \([Ar]\,3d^5\,4s^1\).

1. Understanding Basic Principles:
   • Electronic configuration follows the Aufbau principle, Hund's rule, and the Pauli exclusion principle.
   • The usual order of filling is that electrons fill the \(4s\) orbital before the \(3d\) orbital due to their respective energy levels.
2. Expected Configuration for Chromium:
   • According to the typical filling order, we would expect chromium to have the configuration of \([Ar]\,3d^4\,4s^2\).
   • This is because argon (\([Ar]\)) accounts for the first 18 electrons. Chromium, which has 24 electrons, would then fill the next 6 electrons.
3. Actual Configuration:
   • Chromium has an electronic configuration of \([Ar]\,3d^5\,4s^1\).
   • This configuration is an exception to the typical filling order due to electron stability, with half-filled subshells being more stable due to symmetrical distribution.
   • Increased stability arises from minimized electron repulsions and exchange energy.
4. Analyzing the Options:
   • Option 1: \([Ar]\,3d^4\,4s^1\) - Incorrect. This configuration does not conform to the correct electron filling order considering chromium's known exceptions.
   • Option 2: \([Ar]\,3d^4\,4s^2\) - Incorrect. While this might be expected without exception, it doesn’t account for stability preferences.
   • Option 3: \([Ar]\,3d^5\,4s^1\) - Correct. This is the known stable electron configuration of chromium due to half-filled \(d\) subshell stability.
   • Option 4: \([Ar]\,3d^5\,4s^2\) - Incorrect. Chromium doesn't have enough electrons to fill this configuration.\
5. Conclusion: The electron configuration \([Ar]\,3d^5\,4s^1\) is the most stable configuration for chromium, conforming with known principles of electronic stability and exceptions.