Question:
The electronic configuration which is associated with highest first ionisation enthalpy is:
The electronic configuration which is associated with highest first ionisation enthalpy is:
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Half-filled (\(p^3\), \(d^5\), \(f^7\)) and fully-filled subshells possess extra stability and generally show higher ionisation enthalpies than expected.
Updated On: Jul 18, 2026
- \([Ne]\,3s^2 3p^2\)
- \([Ne]\,3s^2 3p^3\)
- \([Ne]\,3s^2 3p^4\)
- \([Ne]\,3s^2 3p^1\)
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The Correct Option is B
Solution and Explanation
Step 1: Identify the elements corresponding to the configurations.
\[ [Ne]\,3s^2 3p^1 \rightarrow Al \] \[ [Ne]\,3s^2 3p^2 \rightarrow Si \] \[ [Ne]\,3s^2 3p^3 \rightarrow P \] \[ [Ne]\,3s^2 3p^4 \rightarrow S \]
Step 2: Recall the trend of first ionisation enthalpy.
Across a period, first ionisation enthalpy generally increases due to increasing effective nuclear charge and decreasing atomic size.
However, extra stability of half-filled and fully-filled subshells causes certain exceptions.
Step 3: Analyze the stability of each configuration.
The configuration \[ [Ne]\,3s^2 3p^3 \] has a completely half-filled \(3p\) subshell.
A half-filled subshell possesses extra stability because of: (i) Symmetrical distribution of electrons and (ii) Maximum exchange energy Therefore, removing an electron from this configuration requires more energy.
Step 4: Compare with \(3p^4\).
Although sulfur \(([Ne]\,3s^2 3p^4)\) lies to the right of phosphorus in the periodic table, one electron pair is present in the \(3p\) orbitals.
Electron-electron repulsion makes removal of an electron comparatively easier. Hence, \[ IE_1(P)\gt IE_1(S) \]
Step 5: Final conclusion.
The configuration having the highest first ionisation enthalpy among the given options is \[ \boxed{[Ne]\,3s^2 3p^3} \] corresponding to phosphorus.
\[ [Ne]\,3s^2 3p^1 \rightarrow Al \] \[ [Ne]\,3s^2 3p^2 \rightarrow Si \] \[ [Ne]\,3s^2 3p^3 \rightarrow P \] \[ [Ne]\,3s^2 3p^4 \rightarrow S \]
Step 2: Recall the trend of first ionisation enthalpy.
Across a period, first ionisation enthalpy generally increases due to increasing effective nuclear charge and decreasing atomic size.
However, extra stability of half-filled and fully-filled subshells causes certain exceptions.
Step 3: Analyze the stability of each configuration.
The configuration \[ [Ne]\,3s^2 3p^3 \] has a completely half-filled \(3p\) subshell.
A half-filled subshell possesses extra stability because of: (i) Symmetrical distribution of electrons and (ii) Maximum exchange energy Therefore, removing an electron from this configuration requires more energy.
Step 4: Compare with \(3p^4\).
Although sulfur \(([Ne]\,3s^2 3p^4)\) lies to the right of phosphorus in the periodic table, one electron pair is present in the \(3p\) orbitals.
Electron-electron repulsion makes removal of an electron comparatively easier. Hence, \[ IE_1(P)\gt IE_1(S) \]
Step 5: Final conclusion.
The configuration having the highest first ionisation enthalpy among the given options is \[ \boxed{[Ne]\,3s^2 3p^3} \] corresponding to phosphorus.
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