# Explain why the successive ionisation energies of aluminium show two large increases: one between the third and fourth ionisation energies, and another between the tenth and eleventh ionisation energies.

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

## Mark scheme (4 marks)

1. The first three electrons are removed from the outer (third) shell / n = 3 shell, which is further from the nucleus and more shielded, so less energy is required.
2. The large increase between the 3rd and 4th ionisation energies occurs because the 4th electron must be removed from the second shell (n = 2), which is closer to the nucleus and experiences less shielding, requiring significantly more energy.
3. The second large increase, between the 10th and 11th ionisation energies, occurs because the 11th electron must be removed from the first shell (n = 1), which is closest to the nucleus and has essentially no shielding by inner electrons.
4. The pattern is consistent with aluminium's electron configuration of 2, 8, 3 (1s² 2s² 2p⁶ 3s² 3p¹), confirming that successive ionisation energies provide evidence for the existence of distinct electron shells / energy levels.

## Key terms

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

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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