Why is the first ionization energy of Nitrogen (Z = 7) higher than that of Oxygen (Z = 8)? (Hard)
Answer and explanation
Correct answer: D. Nitrogen has a half-filled 2p^3 subshell providing extra stability
- Step 1: The valence electronic configuration of N is 2s^2 2p^3 (half-filled p-subshell), whereas O is 2s^2 2p^4. Step 2. The half-filled 2p^3 subshell has enhanced stability, and removing an electron from O relieves electron pairing repulsion, making N harder to ionize than O. Answer: Nitrogen has a half-filled 2p^3 subshell providing extra stability. Why not the others: Higher nuclear charge would predict higher ionization for O (which is overridden here); Nitrogen is actually slightly larger than Oxygen; neither period 2 element possesses d-orbitals.
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