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Why is the second ionisation energy of sodium larger than the second ionisation energy of magnesium? A) The attraction between the nucleus and the outer electron is greater in Na⁺ than in Mg²⁺ - CIE - A-Level Chemistry - Question 12 - 2017 - Paper 1
Question 12
Why is the second ionisation energy of sodium larger than the second ionisation energy of magnesium? A) The attraction between the nucleus and the outer electron is... show full transcript
Worked Solution & Example Answer:Why is the second ionisation energy of sodium larger than the second ionisation energy of magnesium? A) The attraction between the nucleus and the outer electron is greater in Na⁺ than in Mg²⁺ - CIE - A-Level Chemistry - Question 12 - 2017 - Paper 1
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C) The outer electron of Na⁺ is more shielded than the outer electron of Mg²⁺.
Answer
This statement is misleading. Shielding is not stronger in Na⁺ compared to Mg²⁺. The effective nuclear charge is higher in Mg²⁺ due to a higher number of protons, thus making it harder to remove an outer electron.
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D) The outer electron of Na⁺ is in the same orbital as the outer electron of Mg²⁺.
Answer
This statement is also incorrect because while both ions are losing electrons from their outermost shell, the nature of their electron configuration indicates a significant difference in their ionisation energies. The second ionisation energy of sodium is larger because once Na loses one electron, it achieves a stable electron configuration while Mg has a more stable configuration already.