Green Chemistry and the Ten Commandments

7. WATER, THE ULTIMATE GREEN SOLVENT: ITS USES AND

ENVIRONMENTAL CHEMISTRY

7.1. H 2 O: SIMPLE FORMULA, COMPLEX MOLECULE

Water, H 2 O, is an amazing chemical compound. It is the true medium of life. Early
life forms developed in water and only much later in their evolution ventured out of
water, but never very far. Our own bodies are largely water. Our blood is a water solution
of sodium chloride and other essential salts, in which are suspended colloidal-sized red
blood cells that carry oxygen from the lungs throughout the body. Even those organisms
that dare to live in water-deficient areas — camels, gila monsters, cactus, and some
poorly washed humans — must have elaborate mechanisms to conserve, store, and
obtain the small quantities of water in their surroundings.
The thing that makes water so special is its molecular structure represented in Figure
7.1. Recall that the oxygen atom in the water molecule has a stable octet of valence
electrons. These 8 electrons are grouped into 4 pairs. Two of these pairs are shared with

O

H

O

H H

O

H

H

O

H

(+)

(-)

Shared pair

of electrons

in H-O bond

Unshared pair

of electrons

Rotate 90 ̊

Hydrogen bond

connecting two

water molecules

Figure 7.1. The water molecule (left) is electrically polar and has 2 pairs of valence electrons in H-O bonds
and 2 unshared pairs, both of which are shown when the molecule is rotated (middle). The unshared pairs
of electrons can form hydrogen bonds to other water molecules (right).