# Question #a162a

Jul 29, 2016

Valence bond (VB) theory states that a covalent bond is formed by the overlap of two atomic orbitals.

#### Explanation:

There are three basic postulates to VB theory.

1. A sigma (σ) bond forms when two orbitals overlap along the internuclear axis.

A σ bond has the maximum orbital overlap in the region between the two nuclei.

2. A pi (π) bond forms when two atomic orbitals overlap outside of the internuclear axis.

3. The strongest bonds form when there is maximum overlap of orbitals.

Hence, a π bond is weaker than a σ bond.

Modern Valence Bond theory extends these postulates to include the concepts of hybridization (e.g. $s {p}^{3} , s {p}^{2} , s p$) and resonance.

It cannot predict the shapes of molecules, but we can use it to explain the shapes.