The bond that exists between any two molecules is called molecular bonding. The shape of any two molecules is determined by different factors. Based on the molecular geometry, there are several theories to predict the structure, geometry and shape of the molecule. They are:
1. Valence Shell Electron Pair Repulsion (VSEPR) Theory
2. Valance Bond Theory
3. Molecular Orbital Theory
1. Valence Shell Electron Pair Repulsion (VSEPR) Theory:
This theory was proposed by Gillespie and Nyholm in 1957. It is based on the effect of electron repulsion on the bond angle.
Assumptions of VSEPR Theory:
- In a covalent molecule, there is a central atom to which other atoms are attached.
- The central atom contains electron pair which may be lone pair or bond pair.
- The repulsion between the molecule decreases in the order. i.e., lone pair-lone pair > lone pair-bond pair > bond pair-bond pair.
- The molecules are arranged in such a way that they will have minimum repulsion between them.
- If the central atom contain both lone pair and bond pair, then the molecule will have irregular geometry, if the molecule have only bond pair, then the molecule will have regular geometry.
Limitations of VSEPR Theory:
- It doesn’t explain the shape of the molecule having very polar bond.
- It doesn’t explain the shape of certain compound which has inert pair of electron.
- This theory fails to explain the shape of certain compounds of transitional element.