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The molecular structure of water is consistent with a tetrahedral arrangement of two lone pairs and two bonding pairs of electrons. Thus we say that the oxygen atom is sp 3 hybridized, with two of the hybrid orbitals occupied by lone pairs and two by bonding pairs. Since lone pairs occupy more space than bonding pairs, structures that contain lone pairs have bond angles slightly distorted from the ideal. Perfect tetrahedra have angles of 109.5°, but the observed angles in ammonia (107.3°) and water (104.5°) are slightly smaller. Other examples of sp 3 hybridization include CCl 4 , PCl 3 , and NCl 3 .

sp 3 d And sp 3 d 2 Hybridization

To describe the five bonding orbitals in a trigonal bipyramidal arrangement, we must use five of the valence shell atomic orbitals (the s orbital, the three p orbitals, and one of the d orbitals), which gives five sp 3 d hybrid orbitals . With an octahedral arrangement of six hybrid orbitals, we must use six valence shell atomic orbitals (the s orbital, the three p orbitals, and two of the d orbitals in its valence shell), which gives six sp 3 d 2 hybrid orbitals . These hybridizations are only possible for atoms that have d orbitals in their valence subshells (that is, not those in the first or second period).

In a molecule of phosphorus pentachloride, PCl 5 , there are five P–Cl bonds (thus five pairs of valence electrons around the phosphorus atom) directed toward the corners of a trigonal bipyramid. We use the 3 s orbital, the three 3 p orbitals, and one of the 3 d orbitals to form the set of five sp 3 d hybrid orbitals ( [link] ) that are involved in the P–Cl bonds. Other atoms that exhibit sp 3 d hybridization include the sulfur atom in SF 4 and the chlorine atoms in ClF 3 and in ClF 4 + . (The electrons on fluorine atoms are omitted for clarity.)

Three Lewis structures are shown along with designations of molecular shape. The left image shows a sulfur atom singly bonded to four fluorine atoms. The sulfur atom has one lone pair of electrons while each fluorine has three. Two fluorine atoms are drawn vertically up and down from the sulfur while the other two are shown going into and out of the page. The second structure shows one chlorine atom singly bonded to three fluorine atoms. The chlorine has two lone pairs of electrons while each fluorine has three. Two fluorine atoms are drawn vertically up and down from the sulfur while the other is shown horizontally. The right structure shows a chlorine atom singly bonded to four fluorine atoms. The chlorine atom has one lone pair of electrons and a superscript plus sign, while each fluorine has three lone pairs of electrons. Two fluorine atoms are drawn vertically up and down from the sulfur while the other two are shown going into and out of the page.
The three compounds pictured exhibit sp 3 d hybridization in the central atom and a trigonal bipyramid form. SF 4 and ClF 4 + have one lone pair of electrons on the central atom, and ClF 3 has two lone pairs giving it the T-shape shown.
Two images are shown and labeled “a” and “b.” Image a depicts a ball-and-stick model in a trigonal bipyramidal arrangement. Image b depicts the hybrid orbitals in the same arrangement and each is labeled, “s p superscript three d.”
(a) The five regions of electron density around phosphorus in PCl 5 require five hybrid sp 3 d 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).

The sulfur atom in sulfur hexafluoride, SF 6 , exhibits sp 3 d 2 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 3 s orbital, the three 3 p orbitals, and two of the 3 d orbitals form six equivalent sp 3 d 2 hybrid orbitals, each directed toward a different corner of an octahedron. Other atoms that exhibit sp 3 d 2 hybridization include the phosphorus atom in PCl 6 , the iodine atom in the interhalogens IF 6 + , IF 5 , ICl 4 , IF 4 and the xenon atom in XeF 4 .

Two images are shown and labeled “a” and “b.” Image a depicts a ball-and-stick model in an octahedral arrangement. Image b depicts the hybrid orbitals in the same arrangement and each is labeled, “s p superscript three d superscript two.”
(a) Sulfur hexafluoride, SF 6 , has an octahedral structure that requires sp 3 d 2 hybridization. (b) The six sp 3 d 2 orbitals form an octahedral structure around sulfur. Again, the minor lobe of each orbital is not shown for clarity.
Practice Key Terms 7

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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