When the central atom is surrounded by four things, it has a
tetrahedral geometry, with 109.5o angles between the bonds.
| Type | Bond Angle | Example | Lewis Structure |
| AX4: Tetrahedral | 109.5o | CH4 |  |
If one of the bonded atoms is replaced by a lone pair, the molecule assumes a
pyramidal geometry, with a 109.5o angle between the bonds. If
two bonded atoms are replaced by lone pairs, the molecule assumes a bent
geometry with a 109.5o angle between the bonds.
| Type | Bond Angle | Example | Lewis Structure |
| AX3E: Pyramidal | 109.5o | NH3 |  |
| AX2E2: Bent | 109.5o | H2O |  |
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