Why are the trends and exceptions to the trends in ionization energy observed? Check all that apply.

Across a period, nuclear charge increases while added electrons enter the same main energy level, so the attraction to the outer electrons generally grows and ionization energy rises. This supports both “nuclear charge increases” and “electrons are added to the same main energy level.” Group 13 elements have a higher-energy p electron than the s electron removed from Group 2; the filled s orbital shields that p electron, making it easier to remove. Down a group, ionization energy generally decreases, so A is wrong. Group 16’s exception involves repulsion between paired p electrons, not an electron entering an unfilled p orbital, so D is wrong.

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