Catalonia PAU Chemistry Practice Questions - Catalonia PAU Chemistry Examination - CIC Generalitat De Catalunya (Química 2n Batxillerat 2026) Exam

Why is the first ionization energy of Magnesium (Z = 12, 738 kJ/mol) higher than that of Aluminum (Z = 13, 578 kJ/mol)?

Magnesium has a larger nuclear charge than Aluminum. Aluminum's valence electron is removed from a higher-energy 3p subshell that is shielded by filled 3s orbitals. Magnesium has a smaller atomic radius than Aluminum. Aluminum forms a stable noble gas core upon losing one electron.

Correct Answer:

Aluminum's valence electron is removed from a higher-energy 3p subshell that is shielded by filled 3s orbitals.

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