Shapes of Molecules
The shapes of molecules and angles between the different atoms can be predicted using electron pair repulsion theory. This uses two main principles:
- Electron pairs around atoms repel each other
- Therefore electron pairs will space themselves as far apart as possible from each other
The shape of the molecule and therefore its bond angles can be predicted by working out how many electron pairs surround the central atom and applying these principles. The table below summarizes the main shapes you need to know for the exam.
| Electron Pairs | Bonding Pairs | Lone Pairs | Shape | Bond Angle |
| 2 | 2 | 0 | Linear | 180° |
| 3 | 3 | 0 | Trigonal Planar | 120 ° |
| 3 | 2 | 1 | Bent | 119° |
| 4 | 4 | 0 | Tetrahedral | 109.5 ° |
| 4 | 3 | 1 | Trigonal Pyramidal | 107° |
| 4 | 2 | 2 | Bent | 104.5° |
| 5 | 5 | 0 | Trigonal Bipyramidal | 120°, 90° |
| 6 | 6 | 0 | Octahedral | 90° |
Remember that the biggest angles are between two lone pairs. Lone pair/bonding pair angles are the second biggest, and bonding pair/bonding pair angles the smallest.
