Organic Structures - Organic Chemistry Concepts: An EFL Approach - page 5

1.4 BONDS AND SHAPE: THE HYBRIDIZATION
MODEL
To understand organic chemistry, we must understand bonding and shape, espe-
cially that of carbon. At this level of study, we can use the simple hybridiza-
tion model to explain single and multiple bonding, as well as molecular shape.
Hybridization is the mixing of atomic orbitals to give new hybrid atomic orbit-
als which have new shape and directional properties. These hybrid atomic orbit-
als then combine with other atomic orbitals to form the bonds in molecules.

Table 1.3 Hybridization States of Carbon

sp 2 sp 3

sp

Number of orbitals 2 3 4

Interorbital angle 180° 120° 109.5°

Orbital arrangement Linear Trigonal Tetrahedral

Remaining p orbitals 2 1 0

Bonds formed 2 σ , 2 π 3 σ , 1 π 4 σ

% s character 50 33 ⅓ 25

% p character 50 66 ⅔ 75

Carbon electronegativity 3.29 2.75 2.48

C-C bond length (pm) 121 133 154

Average C-C bond energy (kJ/mol) 837 620 347

Carbon has one 2 s and three 2 p orbitals for use in hybridization. Table 1.3 shows
that the combination of the 2 s orbital with three, two, or one 2 p orbital leads
to 4 sp 3 , 3 sp 2 , and 2 sp hybrid atomic orbitals. Figures 1.3-1.5 show that all three
of these results give the tetravalency that carbon needs by allowing for single or
multiple bonds to be present.

FIGURE 1.3
sp 3 -hybridized carbon (tetrahedral, four single σ bonds).