Why does boron have a lower first ionization energy than beryllium (801 vs 899 kJ/mol)?
Answer and explanation
Correct answer: C. The 2p electron in boron is higher in energy and shielded by the filled 2s subshell
Beryllium has a completely filled 2s subshell ([He] 2s2). In boron ([He] 2s2 2p1), the single 2p electron is at a higher energy level and is shielded from the nucleus by the 2s electrons, making its removal require less energy.
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