According to VSEPR theory, the shape of a molecule or ion of the type AXn depends on the total number of bonding and nonbonding electron pair regions at A. The summary below shows the possible shapes for molecules having three or four electron pair regions about a central atom.
Successive replacement of bonded atoms X by nonbonding electron pairs E
This activity is concerned with deducing the shape of an ion or molecule that has up to six electron pair regions at the central atom. On completing the activity you should be able to deduce, for a molecule or ion,
Successive replacement of bonded atoms X by nonbonding electron pairs E
- does not change the arrangement of electron pair regions about atom A,
- does change the shape descriptor because this describes the location of outer atoms.
- changes the angle between adjacent AX bonds because non-bonding electron pairs at A occupy more space at A than bonding electron pairs.
| AX3 | AX2E |
 |  |
| trigonal planar | bent |
| AX4 | AX3E | AX2E2 |
 |  |  |
| tetrahedral | trigonal pyramid | bent |
This activity is concerned with deducing the shape of an ion or molecule that has up to six electron pair regions at the central atom. On completing the activity you should be able to deduce, for a molecule or ion,
- the number of electron pair regions at a central atom
- the types of electron pair regions at the central atom
- the orientation of the electron pair regions at the central atom
- the shape of the molecule or ion