The shape of a molecule describes the location of the outermost atoms.
Valence Shell Electron Pair Repulsion (VSEPR) Theory predicts the shape of molecules by assuming that the electron pair domains at the central atom occupy positions as far apart as possible.
These orientations adopted by the bonding pair domains in molecules AXn where there are no nonbonding (lone) pairs at A are shown below for n between 2 and 4. Bonds depicted by a
Note the description of each shape, and that the angle between adjacent A-X bonds depends on the shape.
How do I know which compounds have no non-bonding electron pairs at the central atom?
Valence Shell Electron Pair Repulsion (VSEPR) Theory predicts the shape of molecules by assuming that the electron pair domains at the central atom occupy positions as far apart as possible.
There are two types of electron pair domains (regions).
Bonding electron pair domains (regions) are between atoms and contain one or more bonding electron pairs.
Nonbonding electron pair domains (regions) are at an atom each have one nonbonding electron pair.
Bonding electron pair domains (regions) are between atoms and contain one or more bonding electron pairs.
Nonbonding electron pair domains (regions) are at an atom each have one nonbonding electron pair.
These orientations adopted by the bonding pair domains in molecules AXn where there are no nonbonding (lone) pairs at A are shown below for n between 2 and 4. Bonds depicted by a
solid line are in the plane of the screen.
solid wedge point to atoms in front of the plane of the screen.
hashed wedge point to atoms behind the plane of the screen.
solid wedge point to atoms in front of the plane of the screen.
hashed wedge point to atoms behind the plane of the screen.
| AX2 | AX3 | AX4 |
 |  |  |
| linear | trigonal planar | tetrahedral |
Note the description of each shape, and that the angle between adjacent A-X bonds depends on the shape.
The angle between adjacent A-X bonds is the same for all bonds around A.
How do I know which compounds have no non-bonding electron pairs at the central atom?
The number of bonding and non-bonding electron pair domains can be deduced from the Lewis structure for the compound.