SINF6 Chemistry Practice Questions - Solomon Islands National Form Six Examination - Chemistry Exam

Which statement best explains why aluminum (Z = 13) has a lower first ionization energy than magnesium (Z = 12)?

The outermost electron in aluminum is in a 3p subshell, which is higher in energy and shielded by the 3s subshell. Aluminum has a smaller nuclear charge than magnesium, so it holds its electrons less tightly. The 3s subshell of aluminum experiences greater electron-electron repulsion than that of magnesium. Aluminum forms a stable noble gas configuration upon losing two electrons.

Correct Answer:

The outermost electron in aluminum is in a 3p subshell, which is higher in energy and shielded by the 3s subshell.

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