What are molecular orbital theory and valence bond theory? What does molecular orbital theory explain that valence bond theory does not?
MO theory predicts the distribution of electrons in a molecule. This helps predict properties such as bond order, shape, and electrical properties.
Valence Bond (VB) theory and Lewis Structures explain the properties of simple molecules. Molecular Orbital (MO) theory better explains the properties of more complex molecules.
MO theory explains the partial bonds of NO₃⁻ without using resonance. This makes MO theory more useful for the description of extended π systems.
Also, in benzene the six p electrons are in three molecular π orbitals around the ring. These orbitals spread the six electrons evenly over all the carbon atoms. All carbon-carbon bonds in benzene are equivalent. There is no need to use resonance.
MO theory also explains other properties better than VB theory.