Question

a. what structural feature seems to distinguish the molecules where the real bond angle is less than the model bond angle?

Explanation:

Lone pairs of electrons on the central atom cause greater repulsion than bonding pairs. This extra repulsion pushes the bonding pairs closer together, reducing the bond angle. For example, in \(H_2O\), the oxygen atom has two lone pairs. These lone pairs repel the \(O - H\) bonding pairs more strongly than the bonding pairs repel each other. As a result, the bond angle in \(H_2O\) (\(104.5^{\circ}\)) is less than the tetrahedral model bond angle (\(109.5^{\circ}\)).

Answer:

Molecules with lone pairs of electrons on the central atom have real bond angles less than model bond angles.