The letters in VSEPR stand for valence shell electron pair
repulsion. In 1957, the Canadian chemist R.J. Gillespie,
while at McMaster University, developed the VSEPR
theory along with a scientist named Nyholm.
This theory is used to predict the shapes of molecules.
The main proponent of the theory is that the shape of a
molecule is determined by the pairs of bonding and
nonbonding electrons around the central atom in the
molecule.
These pairs of electrons will try to stay away from each
other in order to minimize all the repulsive forces
between them, since electrons are negative and like
charges repel. The main concept is to minimize the
overall repulsive forces between all pairs of electrons
and not just any two pairs of electrons.
Bonding pairs and lone pairs of electrons in the valence
level of an atom repel one another due to their negative
charges.
The pairs of electrons take up positions as far from each
other as possible about the spherical central atom while
remaining in the molecule.
The lone pair (LP) will spread more than bonding pair
(BP).
The order of repulsion can be expressed as follows:
LP-LP > LP-BP > BP-BP
Do Practice Problems
6 & 7. Page 193