Organic Chemistry

28 CHAPTER 1 Electronic Structure and Bonding • Acids and Bases

faces, each an equilateral triangle). Each of the four bonds in methane is

formed from overlap of an orbital of carbon with the sorbital of a hydrogen

(Figure 1.12b). This explains why the four bonds are identical.

The angle formed between any two bonds of methane is 109.5°. This bond angle is

called the tetrahedral bond angle. A carbon, such as the one in methane, that forms

covalent bonds using four equivalent orbitals is called a tetrahedral carbon.

The postulation of hybrid orbitals may appear to be a theory contrived just to make

things fit—and that is exactly what it is. Nevertheless, it is a theory that gives us a very

good picture of the bonding in organic compounds.

Note to the student

It is important to understand what molecules look like in three dimensions. As you study

each chapter, make sure to visit the Web site http://www.prenhall.com/bruice and look at the

three-dimensional representations of molecules that can be found in the molecule gallery

that accompanies the chapter.

Bonding in Ethane

The two carbon atoms in ethane are tetrahedral. Each carbon uses four orbitals to

form four covalent bonds:

One orbital of one carbon overlaps an orbital of the other carbon to form

the bond. Each of the remaining three orbitals of each carbon overlaps

the s orbital of a hydrogen to form a bond. Thus, the bond is

formed by overlap, and each bond is formed by overlap

(Figure 1.13). Each of the bond angles in ethane is nearly the tetrahedral bond angle

of 109.5°, and the length of the bond is 1.54 Ethane, like methane, is a

nonpolar molecule.

C¬C Å.

sp^3 – sp^3 C¬H sp^3 – s

C¬H C¬C

C¬C sp^3

sp^3 sp^3

H C

H

H

C

H

H

H

ethane

sp^3

sp^3

C¬H

sp^3

C¬H

H H

H H

H H HH

H H

HH

CC CC

Electron pairs spread themselves into
space as far from each other as possible.

Figure 1.13

An orbital picture of ethane. The bond is formed by overlap, and each

bond is formed by sp^3 – soverlap. (The smaller lobes of the sp^3 orbitals are not shown.)

C¬C sp^3 – sp^3 C¬H

perspective formula

of ethane

ball-and-stick model

of ethane

1.54 A°

1.10 A° 109.6°

space-filling model

of ethane

electrostatic potential

map for ethane

C C

H

H

H

H

H

H

3-D Molecule:

Methane