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.
The orientations adopted by the bonding pair domains in molecules AXn where there are no nonbonding (lone) pairs A are shown below for n between 2 and 6.
Bonds depicted by
Note the description of each shape, and that the angle between adjacent A-X bonds depends on the shape.
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.
Bonding electron pair domains may have one or more bonding electron pairs.
Nonbonding electron pair domains each have one nonbonding electron pair.
Bonding electron pair domains may have one or more bonding electron pairs.
Nonbonding electron pair domains each have one nonbonding electron pair.
The orientations adopted by the bonding pair domains in molecules AXn where there are no nonbonding (lone) pairs A are shown below for n between 2 and 6.
Bonds depicted by
solid lines are in the plane of the screen.
solid wedges point to atoms in front of the plane of the screen.
hashed wedges point to atoms behind the plane of the screen.
solid wedges point to atoms in front of the plane of the screen.
hashed wedges point to atoms behind the plane of the screen.
| AX2 | AX3 | AX4 |
 |  |  |
| linear | trigonal planar | tetrahedral |
| AX5 | AX6 |
 |  |
| trigonal bipyramid | octahedral |
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 except for the trigonal bipyramid shape.
For the trigonal bipyramid,
bonds around the middle (equator) are referred to as equatorial.
bonds that stick up and down are referred to as axial.
the angle between adjacent equatorial A-X bonds is 120°.
the angle between an equatorial A-X bond an an axial A-X bond is 90°.
For the trigonal bipyramid,
bonds around the middle (equator) are referred to as equatorial.
bonds that stick up and down are referred to as axial.
the angle between adjacent equatorial A-X bonds is 120°.
the angle between an equatorial A-X bond an an axial A-X bond is 90°.