Quantum Numbers

Neutral Copper ( $Z = 29$ ): Configuration is an exception to Aufbau: $[A r] 3 d^{10} 4 s^{1}$ .
Ionization Rules: Electrons are first removed from the shell with the highest principal quantum number ( $n$ ).
Forming $C u^{2 +}$ :
- Remove $1$ electron from $4 s$ : yields $C u^{+} ([A r] 3 d^{10})$ .
- Remove $1$ electron from $3 d$ : yields $C u^{2 +} ([A r] 3 d^{9})$ .
Orbital Analysis: The $d^{9}$ configuration consists of $5$ orbitals. Following Hund's rule, $4$ orbitals are fully paired and $1$ orbital has a single unpaired electron.
Conclusion: Copper(II) ions are paramagnetic due to this one unpaired electron.

This medium difficulty chemistry question is from the chapter atomic structure, covering the topic of quantum numbers. It appeared in the 2025 exam.

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Quantum Numbers

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