CHAPTERS 8 & 9.1: BONDINg
Rocks, coal, soil, petroleum, trees, and human bodies are all complex mixtures of chemical compounds in which different kinds of atoms are bound together. Substances composed of unbound atoms do exist in nature, but they are very rare. Examples are the argon in the atmosphere and the helium mixed with natural gas reserves. The manner in which atoms are bound together has a profound effect on chemical and physical properties. For example, graphite is a soft, slippery material used as a lubricant in locks, and diamond is one of the hardest materials known, valuable as both a gemstone and in industrial cutting tools. Why do these materials, both composed solely of carbon atoms, have such different properties? The answer, as we will see, lies in the bonding in these substances. Molecular bonding and structure play the central role in determining the course of all chemical reactions, many of which are vital to our survival. All of these fundamental biological reactions hinge on the geometric structure of molecules, sometimes depending on very subtle differences in molecular shape to channel the chemical reaction one way rather than the other.