# Explain why the bond angle in water (H₂O) is less than the bond angle in ammonia (NH₃), and why both are less than the tetrahedral angle of 109.5°.

> IB DP Chemistry Higher Level (2023 syllabus) — S2.2 The covalent model · Explain · 4 marks

## Mark scheme (4 marks)

1. Both water and ammonia have a tetrahedral electron domain geometry (four electron domains around the central atom), so the ideal/reference angle is 109.5°.
2. Lone pairs occupy more space / exert greater repulsion than bonding pairs because lone pair electrons are held closer to the central atom and are not constrained between two nuclei.
3. Ammonia has one lone pair and three bonding pairs; the one lone pair compresses the three H–N–H bond angles below 109.5° to approximately 107°.
4. Water has two lone pairs and only two bonding pairs; the greater lone pair repulsion (two lone pairs) compresses the H–O–H bond angle further to approximately 104.5°, which is less than in ammonia.

## Key terms

- [bond angle](https://www.gradenine.co.uk/glossary/bond-angle)
- [tetrahedral](https://www.gradenine.co.uk/glossary/tetrahedral)

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-the-bond-angle-in-2bfa59ad) · Published by Druglandscape Ltd.