Inorganic and Applied Chemistry

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Inorganic and Applied Chemistry

In the previous example we have just seen how a double bond consists of one-bond and one-bond. In the

case with the linear carbon dioxide molecule, the central carbon atom is double bonded to each of the two

oxygen atoms which we saw in Example 2- H on page 61. How is that possible? The answer is given in the

following example.

Example 2- O:

CO 2 molecule, sp-hybridization

From the Lewis structure of the carbon dioxide molecule (Figure 2- 18a) it is seen that the carbon atom is

surrounded by two electron groups (two double bonds). Two electron groups mean that there is a need for

two identical orbitals 180o apart according to the VSEPR theory and Table 2- 1 on page 70. The carbon

atom solves this problem by forming two identical so-called sp-hybrid orbital. As the name sp indicated

these orbitals are made from one s-orbital and one p-orbital.

sp hybrid orbitals

p orbital

s orbital















2

1

1

Hencetwo of the atomic p-orbitals in the carbon atom remain unchanged. From the Lewis structure it is

also seen that each oxygen atom is surrounded by three electron groups (2 lone pairs and 1 double bond).

In Example 2- N on page 74 we saw that three electron groups around an atom results in sp^2 hybridization.

Thus the carbon atom is sp-hybridized and the two oxygen atoms are each sp^2 hybridized. This is sketched

in Figure 2- 18b.

Figure 2- 18: sp-hybridization in CO 2

(a) Lewis structure of a carbon dioxide molecule. (b) The carbon atom is sp-hybridized (two yellow sp-

orbitals) while the two oxygen atoms are sp^2 hybridized (2×3 green sp^2 -orbitals). The double bonds each

consist of an -bond (overlap of a sp-orbital and a sp^2 -orbital) and a -bond in the space between one p-

orbital from the carbon atom and one from the oxygen atom. The p-orbitals are blue on the figure while

the -bonds are indicated with dotted lines.

Again we see that in double bonds we have -bonds in the overlap between hybrid orbitals and -bonds in

the space between atomic p-orbitals. Thus in the case of carbon dioxide the two -bonds are rotated 90o

relative to each other.

Chemical compounds