What is the Difference Between Molecular Orbital Theory and Valence Bond Theory?

The main differences between Molecular Orbital Theory (MOT) and Valence Bond Theory (VBT) are:

1. Focus: VBT considers a molecule as a collection of bonds, whereas MOT views the molecule as a whole.
2. Electron Distribution: VBT assumes that electrons in a molecule are simply the electrons in the original atomic orbitals, with some used while bonding. It does not account for the true distribution of electrons within molecules, but instead treats electrons as if they are "localized" on the atoms themselves. On the other hand, MOT accounts for the "delocalization" of electrons and describes the electron distribution based on the molecular orbitals formed by the combination of atomic orbitals.
3. Bond Formation: In VBT, the atomic orbitals combine to form new molecular orbitals, with the same number of molecular orbitals as there were atomic orbitals. In MOT, the bond formation is due to the overlap of atomic orbitals and the formation of localized bonds.
4. Resonance: Resonance plays a crucial role in VBT, while it is not required in MOT.

In summary, VBT focuses on the localized bond formation and electron distribution in atomic orbitals, while MOT considers the molecule as a whole and accounts for the delocalization of electrons in molecular orbitals. Both theories are important and provide different perspectives on chemical bonding.

Comparative Table: Molecular Orbital Theory vs Valence Bond Theory

Here is a table comparing Molecular Orbital Theory and Valence Bond Theory:

In summary, Molecular Orbital Theory focuses on the delocalization of electrons throughout the molecule and explains bonding through bonding molecular orbitals. On the other hand, Valence Bond Theory describes chemical bonding by combining atomic orbitals and is more focused on the formation of covalent bonds between atoms.