1. Valence Bond Theory

2. How do bonds form?
The valence bond model or atomic orbital model was developed by Linus Pauling in order to explain how atoms come together and form molecules.
The model theorizes that a covalent bond forms when two orbitals overlap to produce a new combined orbital containing two electrons of opposite spin.
This overlapping results in a decrease in the energy of the atoms forming the bond.
The shared electron pair is most likely to be found in the space between the two nuclei of the atoms forming the bonds.

3. Example H2
The newly combined orbital will contain an electron pair with opposite spin just like a filled atomic orbital.

4. Example HF
In hydrogen fluoride the 1s orbital of the H will overlap with the half-filled 2p orbital of the F forming a covalent bond. 

5. Other Points on the Valence Bond Theory
This theory can also be applied to molecules with more than two atoms such as water.
Each covalent bond results in a new combined orbital with two oppositely spinning electrons.
In order for atoms to bond according to the valence bond model, the orbitals must have an unpaired electron.

6. Questions to Answer
Use the valence bond model to show the bonding in the following molecules; BeH2, BH3, CCl4, PCl5, SF6.
Use the valence bond model to show how the bonds in SO42- are formed.