Valence Shell Electron Pair Repulsion

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.
 
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, and each has one nonbonding electron pair.

The orientations adopted by the bonding pair domains in molecules AXn where there are no nonbonding (lone) pairs at A are shown below for n equal to 2, 3, and 4.

Bonds depicted by a

solid line (—) are in the plane of the screen.
solid wedge () point to atoms in front of the screen.
hashed wedge () point to atoms behind the screen.
 
AX2AX3AX4
lineartrigonal planartetrahedral

The angle between each pair of adjacent A-X bonds depends on the shape.