# Explain why the second ionisation energy of sodium is significantly greater than its first ionisation energy.

> IB DP Chemistry Standard Level (2023 syllabus) — S1.3 Electron configurations · Explain · 4 marks

## Mark scheme (4 marks)

1. The first ionisation energy involves removal of the outermost electron from the third shell (3s¹), which is far from the nucleus / well shielded.
2. After the first ionisation, the sodium ion (Na⁺) has the electron configuration of neon / a full second shell (2s²2p⁶).
3. The second electron must be removed from the second shell, which is closer to the nucleus and experiences less shielding / greater effective nuclear charge.
4. Therefore, considerably more energy is required to overcome the stronger attraction between the nucleus and this inner-shell electron, making the second ionisation energy much larger.

## Key terms

- [ionisation energy](https://www.gradenine.co.uk/glossary/ionisation-energy)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-second-ionisation-energy-46aa0a17) · Published by Druglandscape Ltd.