Question

Number of unpaired electrons in Cu$^{2+$ (Z = 29) is –}

• A. 1
• B. 2
• C. 3
• D. 4

Hint:

Always remember: In transition metals, electrons are lost first from the 4s orbital and then from 3d. For Cu$^{2+}$, the stable configuration is 3d$^9$ with one unpaired electron.

Answer 1

The Correct Option is A

Step 1: Write electronic configuration of neutral Cu (Z = 29).
Copper has an anomalous configuration: \[ \text{Cu (Z=29)} : [Ar] \, 3d^{10} \, 4s^1 \]

Step 2: Write configuration of Cu$^{2+$.}
For Cu$^{2+}$, remove 2 electrons: first from 4s and then from 3d orbital.
\[ \text{Cu}^{2+} : [Ar] \, 3d^9 \]

Step 3: Count unpaired electrons.
The 3d$^9$ configuration has 9 electrons in the d-orbitals: \[ \uparrow\downarrow \; \uparrow\downarrow \; \uparrow\downarrow \; \uparrow\downarrow \; \uparrow \] Thus, there is 1 unpaired electron.
Step 4: Final Answer.
Hence, the number of unpaired electrons in Cu$^{2+}$ is 1.
\[ \boxed{1} \]