CHEMICAL BONDING BENT RULE

In a molecule, smaller bond angles are formed between electronegative ligands since the central atom, to which the ligands are attached, tends to direct bonding hybrid orbitals of greater p character towards its more electronegative substituents.

The rule states: “atomic s character tends to concentrate in orbitals that are directed toward electropositive groups and atomic p character tends to concentrate in orbitals that are directed toward electronegative groups”.  Bent based his rule on the perturbation theory, and suggested that isovalent orbital hybridization should transfer more s character to the more electropositive-bonding orbital to maximize bonding energy Hybrid orbitals for main group elements consist of one s and three p orbitals, with the s orbital having lower energy. To have more s character means that the bonding orbital is lower in energy and shaped more like an s orbital rather than a p orbital In other words, ligand orbitals tend to be rich in p character because of higher electronegativity, with s character concentrated on the central metal. However, in cases where the metal has a lone pair, the lone pair orbital is high in s character. This is because s orbitals are closer to the nucleus, allowing for greater stabilization of the lone pair.