sp³d and sp³d² Hybridization

To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell atomic orbitals. These include the s orbital, the three p orbitals, and one of the d orbitals. This combination results in five sp3d hybrid orbitals.

For an octahedral arrangement, we need six hybrid orbitals. This requires six valence shell atomic orbitals: the s orbital, the three p orbitals, and two of the d orbitals. This creates six sp3d2 hybrid orbitals. Such hybridizations are possible only for atoms with d orbitals in their valence subshells. This excludes atoms in the first and second period of the periodic table.

PCl5, SF4, ClF3 and ClF4 Hybridization

In a molecule of phosphorus pentachloride, PCl5, five P–Cl bonds direct five pairs of valence electrons from the phosphorus atom. These electrons point towards the corners of a trigonal bipyramid. To form the P-Cl bonds, we use the 3s orbital, the three 3p orbitals, and one of the 3d orbitals. This combination creates five sp3d hybrid orbitals ([link]). Other atoms that exhibit sp3d hybridization include the sulfur atom in SF4 and the chlorine atoms in ClF3 and in $ClF_4^+$.

(The electrons on fluorine atoms are omitted for clarity. However, you would need to include them in order for a question to be marked correctly. Your instructor will not know if you understand that they should be there.)

The three compounds pictured exhibit sp3d hybridization in the central atom and a trigonal bipyramid form. SF4 and   $ClF_4^+$ have one lone pair of electrons on the central atom, and ClF3 has two lone pairs giving it the T-shape shown.
(a) The five regions of electron density around phosphorus in PCl5 require five hybrid sp3d orbitals. (b) These orbitals combine to form a trigonal bipyramidal structure with each large lobe of the hybrid orbital pointing at a vertex. As before, there are also small lobes pointing in the opposite direction for each orbital (not shown for clarity).

SF6 Hybridization

The sulfur atom in sulfur hexafluoride, SF6, exhibits sp3d2 hybridization. A molecule of sulfur hexafluoride has six bonding pairs of electrons connecting six fluorine atoms to a single sulfur atom. There are no lone pairs of electrons on the central atom. To bond six fluorine atoms, the 3s orbital, the three 3p orbitals, and two of the 3d orbitals combine. This process forms six equivalent sp3d2 hybrid orbitals, each directed toward a different corner of an octahedron. Other atoms that exhibit sp3d2 hybridization include the phosphorus atom in PCl6−,PCl6−,

the iodine atom in the interhalogens $IF_6^+$, $IF_5$, $ICl_4^−$, $IF_4^−$ and the xenon atom in $XeF_4$.

(a) Sulfur hexafluoride, SF6, has an octahedral structure that requires sp3d2 hybridization. (b) The six sp3d2 orbitals form an octahedral structure around sulfur. Again, the minor lobe of each orbital is not shown for clarity.