One of these models is called the Valence Shell Electron Pair Repulsion Theory for Co-valent Bonding. The basic premise of this theory is that molecules will be shaped so as to minimize the repulsion that takes place between :

1. Two Bonding pairs of electrons formed between a central atom and an atom attached to the central atom

2. Bonding pair and a non-bonding pair found on the central atom

3. Two non-bonding pairs of electrons found on a central atom of the molecule

These valence shell electrons will repel one another. This repulsion has a tendency to make the molecular system more unstable. The atoms of a molecule will arrange themselves around a central atom so as to MINIMIZE this repulsion and thereby stabilize the molecular system as much as possible. The geometry or shape around the central atom will depend upon

1. The number of atoms attached to the central atom

2. The number of non-bonding pairs found on the central atom

3. The size of any charge buildup as the result of differences in electronegativity between the central atom and an atom attached to it.

4. The degree of symmetry that exists between the attached atoms and the central atom.

There are a number of "molecular profiles" that could be used to classify different geometrical shapes that atoms could orient around a central atom. With these thoughts in mind one can predict the shapes of molecules by considering the four factors above. For this discussion we will use "molecular profiles" The letter "A" will signify the central atom and the letter "B" will signify a single atom or group of atoms bonded to the central atom. In addition, we will divide these profiles into several categories: