Hybridization of Atomic Orbitals II

The trigonal bipyramidal, octahedral, and other molecular shapes can be explained by assuming the participation of 3d orbitals in the process of hybridization.

The phosphorus pentachloride molecule has a trigonal bipyramidal shape, and it contains 5 valence electrons. Phosphorus uses the 3s orbital, the three 3p orbitals, and one of the 3d orbitals to form five sp³d hybrid orbitals that are involved in the phosphorus–chlorine bonds.

Sulfur hexafluoride has an octahedral structure and it contains 6 valence electrons. The 3s orbital, the three 3p orbitals, and two of the 3d orbitals on sulfur form six equivalent sp³d² hybrid orbitals. These six sp³d² orbitals form an octahedral structure around sulfur and participate in the formation of sulfur–fluorine bonds.

The concept of hybridization also provides an explanation for the formation of multiple bonds. The side-on overlap of two p orbitals gives rise to a π bond. 

However, a π-bond can only be formed in double and triple bonds when a σ bond already exists between two atoms. Because the π bond exists on opposite sides of the internuclear axis, π bonds are unable to rotate around this axis.

In the ethene molecule, both carbons exhibit