5 Steps to a 5 AP Chemistry 2019

156 ❯ STEP 4. Review the Knowledge You Need to Score High

One place this type of bonding occurs is in the formation of the carbon-to-carbon double

bond, as will be discussed later.

sp^3 hybridization results from the mixing of one s orbital and three p orbitals, giving four

sp^3 hybrid orbitals with a tetrahedral geometric orientation. This sp^3 hybridization is found

in carbon when it forms four single bonds.

sp^3 d hybridization results from the blending of an s orbital, three p orbitals, and one d

orbital. The result is five sp^3 d orbitals with a trigonal bipyramidal orientation. This type of

bonding occurs in compounds like PCl 5. Note that this hybridization is an exception to

the octet rule.

sp^3 d^2 hybridization occurs when one s, three p, and two d orbitals are mixed, giving

an octahedral arrangement. SF 6 is an example. Again, this hybridization is an exception

to the octet rule. If one starts with this structure and one of the bonding pairs becomes

a lone pair, then a square pyramidal shape results, while two lone pairs give a square

planar shape.

Figure 11.8 shows the hybridization that occurs in ethylene, H 2 C=CH 2. Each carbon

has undergone sp^2 hybridization. On each carbon, two of the hybrid orbitals have over-

lapped with an s orbital on a hydrogen atom, to form a carbon-to-hydrogen covalent

bond. The third sp^2 hybrid orbital has overlapped with the sp^2 hybrid on the other carbon

to form a carbon-to-carbon covalent bond. Note that the remaining p orbital on each

carbon that has not undergone hybridization is also overlapping above and below a line

joining the carbons. In ethylene, there are two types of bond. In sigma (s) bonds, the

overlap of the orbitals occurs on a line between the two atoms involved in the covalent

bond. In ethylene, the C–H bonds and one of the C–C bonds are sigma bonds. In pi (p)

bonds, the overlap of orbitals occurs above and below a line through the two nuclei of the

atoms involved in the bond. A double bond always is composed of one sigma and one pi

bond. A carbon-to-carbon triple bond results from the overlap of an sp hybrid orbital and

two p orbitals on one carbon, with the same on the other carbon. In this situation, there

will be one sigma bond (overlap of the sp hybrid orbitals) and two pi bonds (overlap of

two sets of p orbitals).

H

H

H

H

CC

H1s H1s

sp^2

sp^2

sp^2 sp^2

sp^2

sp^2

H

C

Combined

unhybridized 2p

H H

H

C

Figure 11.8 Hybridization in ethylene, H 2 C=CH 2.

ENRICHMENT