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?
Select the correct option:
Solution
[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 ✓.
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More electronic configuration Practice Questions
Among the following species, which one has the electronic configuration [Ar] 3d5?
Among the following species, which one has the electronic configuration [Ar] 3d5?
Which of the following electronic configurations violates Hund's rule of maximum multiplicity?
Which of the following electronic configurations violates Hund's rule of maximum multiplicity?
The number of unpaired electrons in Fe²⁺ (Z = 26) is:
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The electronic configuration of chromium (Z = 24) is:
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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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