Question:
High second ionization enthalpies than expected are observed for
High second ionization enthalpies than expected are observed for
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Exceptionally stable half-filled \((d^5)\) and fully filled \((d^{10})\) configurations lead to unusually high ionization enthalpies when an electron has to be removed from them.
Updated On: Jun 18, 2026
- Ti, Zn
- Mn, Fe
- V, Ni
- Cr, Cu
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The Correct Option is D
Solution and Explanation
Step 1: Recall the electronic configurations of Cr and Cu.
Chromium: \[ Cr=[Ar]\,3d^5\,4s^1 \] Copper: \[ Cu=[Ar]\,3d^{10}\,4s^1 \]
Step 2: Remove the first electron.
For chromium, \[ Cr^+=[Ar]\,3d^5 \] which is a half-filled \(d\)-subshell and hence highly stable.
For copper, \[ Cu^+=[Ar]\,3d^{10} \] which is a completely filled \(d\)-subshell and hence highly stable.
Step 3: Consider the second ionization.
The second ionization involves removing an electron from \[ Cr^+ \rightarrow Cr^{2+} \] and \[ Cu^+ \rightarrow Cu^{2+} \] Since \(Cr^+\) has a stable half-filled configuration and \(Cu^+\) has a stable fully filled configuration, removing another electron requires unusually high energy.
Therefore, their second ionization enthalpies are higher than expected.
Step 4: Final conclusion.
Hence, \[ \boxed{\text{Cr, Cu}} \] Therefore, the correct option is (4).
Chromium: \[ Cr=[Ar]\,3d^5\,4s^1 \] Copper: \[ Cu=[Ar]\,3d^{10}\,4s^1 \]
Step 2: Remove the first electron.
For chromium, \[ Cr^+=[Ar]\,3d^5 \] which is a half-filled \(d\)-subshell and hence highly stable.
For copper, \[ Cu^+=[Ar]\,3d^{10} \] which is a completely filled \(d\)-subshell and hence highly stable.
Step 3: Consider the second ionization.
The second ionization involves removing an electron from \[ Cr^+ \rightarrow Cr^{2+} \] and \[ Cu^+ \rightarrow Cu^{2+} \] Since \(Cr^+\) has a stable half-filled configuration and \(Cu^+\) has a stable fully filled configuration, removing another electron requires unusually high energy.
Therefore, their second ionization enthalpies are higher than expected.
Step 4: Final conclusion.
Hence, \[ \boxed{\text{Cr, Cu}} \] Therefore, the correct option is (4).
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