6.2 Covalent Bonding

Plants absorb water through their roots from soil or from a solution containing nutrients, as in Figure 8. Carbon dioxide from the air enters the plants through small openings in their leaves. The plants use the energy from sunlight to convert water and carbon dioxide into a sugar. Energy is stored in the chemical bonds of the sugar.

The elements in sugar are carbon, oxygen, and hydrogen. All three are nonmetals, which have relatively high ionization energies. A transfer of electrons does not tend to occur between nonmetal atoms. So, how are two nonmetals able to form bonds?

Covalent Bonds

You and a friend are participating in a treasure hunt. The rules state that the first person to find all eight items on a list will win a 21-speed bicycle. After about an hour, you have found six of the items on the list and your friend has found the other two. You and your friend have incomplete sets of items. But if you are willing to share your items with your friend, together you will have a complete set of items and qualify for the prize. Of course, you will have to be willing to share the bicycle, too. When nonmetals join together, they display a similar sharing strategy.

Figure 8 When plants are grown in water instead of soil, you can see their roots. Plants absorb water through their roots and carbon dioxide through small openings in their leaves.

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