Electronic Configuration
The ground state electronic configuration of Cu (Z=29) deviates from the expected Aufbau order. Which configuration correctly represents copper in its ground state?
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About This Question
- Subject
- chemistry
- Chapter
- atomic structure
- Topic
- electronic configuration
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
[Ar]3d104s1
The Aufbau principle predicts that electrons fill orbitals in order of increasing energy. However, half-filled and completely filled d subshells are extra stable due to exchange energy and symmetry. For copper (Z=29), the expected configuration would be [Ar] 3d^9 4s^2, but experimental evidence shows the actual configuration is [Ar] 3d^10 4s^1. The reason is that a completely filled 3d^10 subshell has greater stability than a partially filled 3d^9 subshell; this extra stability more than compensates for the energy cost of moving one electron from 4s to 3d. Option [Ar] 3d^9 4s^2 is the predicted-but-incorrect configuration based on naive Aufbau application. Option [Ar] 3d^8 4s^2 4p^1 has 31 electrons, which is incorrect for copper (Z=29). Option [Ar] 3d^10 4s^0 4p^1 also has 29 electrons but places one in 4p, which is much higher in energy than 4s and is not justified. This anomalous configuration of Cu is a high-frequency JEE topic under electronic configuration. Plausibility check: [Ar] has 18 electrons, and [Ar] 3d^10 4s^1 gives 18+10+1=29 ✓.
This easy difficulty chemistry question is from the chapter atomic structure, covering the topic of electronic configuration. It appeared in the 2025 exam.
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