This theory predicts the shapes of molecules. VSEPR stands for:
Valence Shell
Electron Pair
Repulsion
Valence Shell
The outer shell of electrons, the one that is involved in covalent bonding, is called the Valence Shell.
Electron Pair
Each covalent bond is the result of sharing a pair of electrons.
Most atoms do not use all their valence shell electrons in covalent bonding, so some 'lone' pairs of electrons are also found in the valence shell. 'Lone pairs' are also called 'non-bonding pairs'.
VSEPR theory counts all bonds as a single pair of electrons. The extra pair of electrons in a double bond is ignored, and the extra two pairs in a triple bond are ignored.
Repulsion
Each electron pair repels every other electron pair, because of the negative electrical charges of electrons.
VSEPR theory explains how the electron pairs are arranged in space so that the electron pairs are as far away from one another as possible.