Inorganic and Applied Chemistry

Download free books at BookBooN.com

Inorganic and Applied Chemistry

Example 2- N:

C 2 H 4 molecule, sp^2 -hybridization

It is seen from the Lewis structure of C 2 H 4 (Figure 2- 17a) that the two central carbon atoms each are

surrounded by three electron groups (1 double bond and 2 single bonds). Three such electron groups

surrounding the central atom results in a trigonal planar arrangement according to Table 2- 1 on page 70

(from the VSEPR theory). Thus there is a need for three identical orbital with such a trigonal planar

arrangement to host the electron groups. Each carbon atom then transforms one s-orbital and two p-orbitals

into three identical sp^2 -hybrid orbitals. As the name sp^2 indicated, they are “made” from one s-orbital and

two p-orbitals.

sp hybrid orbitals

p orbitals

s orbital













 (^2)
3
2
1
Henceone atomic p-orbital remains unchanged in each carbon atom. The double bond consists in that the
overlap between two sp^2 orbitals constitutes an -bond while a -bond is formed in the space between the
two remaining atomic p-orbitals of the carbon atoms. This is sketched in Figure 2- 17b.
Figure 2- 17: sp^2 -hybridization in C 2 H 4
(a) Lewis structure of an ethene molecule. (b) Each carbon atom is sp^2 hybridized (the 2×3 sp^2 orbitals are
purple on the figure). The double bond consists of an -bond (overlap of the two sp^2 orbitals) and a -bond
in the space between the two p-atomic orbitals. The two p-orbital are blue on the figure while the -bond is
grey on the figure. The bonds to the hydrogen atoms are -bonds.
From the figure it is seen that rotation around the C=C double bond is not possible because the -bond
“locks” the possible of rotation. Thus double bonds are far less flexible compared to single bonds which only
consist of -bonds.
Chemical compounds