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

> IB DP Chemistry Higher Level (2023 syllabus) — S3.1 The periodic table: classification of elements · Explain · 4 marks

## Mark scheme (4 marks)

1. Aluminium has the electron configuration [Ne] 3s² 3p¹ / 2,8,3, so there are three electrons in the third shell (valence electrons).
2. After the third ionisation, the fourth electron is removed from a shell closer to the nucleus (the second shell / n=2), which is more strongly attracted to the nucleus / less shielded, requiring significantly more energy.
3. The large increase between the tenth and eleventh ionisation energies occurs because the tenth electron is the last electron in the second shell (n=2), and the eleventh electron must be removed from the first shell (n=1), which is even closer to the nucleus and has virtually no shielding.
4. In both cases, the large increase arises because the electron being removed is in a shell of lower principal quantum number (closer to the nucleus), experiencing greater effective nuclear charge / less shielding, compared to the preceding electron.

## Key terms

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

## Related

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