Question

What are the limitations of valence bond theory?

Short answer

The primary limitations of Valence Bond Theory include its inability to explain the shapes of molecules, the limitation of electron pair sharing to two atoms, and ineffective contrasting of sigma and pi bonds.

Step-by-step solution

Identifying Limitation #1 - Molecular Shapes

Valence Bond Theory was unable to explain the shapes of molecules. This is due to the theory's focus on the overlapping of orbitals, which doesn't account for how those orbitals orient themselves in space to form distinct molecular shapes.

Identifying Limitation #2 - Restrictions on Electron Pair-Sharing

The theory assumes that covalent bond formation involves the sharing of electron pairs only between two atoms. However, there are certain situations where electrons are delocalized or shared by more than two atoms. This phenomenon isn't explained by Valence Bond Theory.

Identifying Limitation #3 - Sigma and Pi Bonds

The theory is not very effective in contrasting the different properties of Sigma and Pi bonds. In reality, sigma (σ) bonds are directional and stronger, while pi (π) bonds are weaker and more diffused, but the theory does not make this distinction clear.