Chemistry

Question Analysis
This question asks to order Period 2 elements by first ionization energy, considering the N/O exception. The main focus is combining the general period trend with half-filled stability.

Key Concept Explanation
General period trend: Ionization energy increases from left to right.
Exception: Nitrogen (2p³, half-filled stability) has a higher ionization energy than oxygen (2p⁴, paired electron repulsion).
Carbon (2p²) has a lower ionization energy than both N and O.

Step-by-Step Solution
1. List the elements and their valence electron configurations:
C: 2s²2p²
N: 2s²2p³
O: 2s²2p⁴
2. Apply th...