7.1: Anatomy of a Molecule

If you could shrink yourself to a billion times smaller than you are now, a water molecule would be about the size of a footstool. Assuming you could get a water molecule to hold still (they like to jump around like little kids), you could determine that a single water molecule has a diameter of approximately 1.1 × 10^–8 inches, or 280 picometers. (A pico is 10^–12, or 0.000000000001). Stepping back from your tamed water molecule and giving it a look-over, you take a quick breath and cover your mouth: “OMG! It looks like Mickey Mouse.” Indeed, the water molecule—when depicted as the stick-and-ball model of a molecule—resembles Mickey Mouse’s head, big ears and all.

The analogy offers an atomic view of water, too. Mickey’s head and ears represent different atoms, namely, oxygen and hydrogen. One molecule of water consists of one atom of oxygen—Mickey’s head—and two atoms of hydrogen—Mickey’s ears. But the structure of water was discovered long before Mickey. In 1805 French chemist Joseph Louis Gay-Lussac (1778–1850) and famed German biogeographer Alexander von Humboldt (1769–1859) suggested a 2:1 ratio of hydrogen to oxygen (Scott 1887). But before we go any further with Mickey’s head and the structure of water, let’s do some quick basic training in chemistry.

Molecules are composed of atoms, the building blocks of matter, the “stuff” of which the universe is made. Atoms consist of subatomic particles, the number of which determines an atom’s properties and classification. We often visualize atoms as miniature solar systems, where the center of the atom—the nucleus—corresponds to the sun. The electrons, which “orbit” the nucleus, correspond to the planets. The nucleus of an atom is made up of two subatomic particles: protons, subatomic particles with a positive charge, and neutrons, subatomic particles with a neutral charge—that is, no charge. The electrons have a negative charge equal to the proton’s charge, but with the opposite sign.

In the language of chemistry, atoms with the same number of protons represent an element. By definition, elements cannot be broken apart by ordinary chemical reactions. On Earth there are 98 or so naturally occurring elements. These are the individual building blocks of all matter. We find these elements in the ocean, on land, and everywhere else in the universe. Each element—and, therefore, each atom of an element—is unique and has unique properties. Chemists represent elements with one or two letters—their chemical symbol. For example, the chemical symbol for hydrogen is H, and the chemical symbol for oxygen is O. Iron and silicon get two-letter chemical symbols, Fe and Si, respectively. Unknown or synthetic chemicals may receive temporary three-letter symbols (e.g., Chatt 1979).

One way to think of elements is to imagine a Lego set with 98 different varieties of plastic bricks, gears, Figures, and so forth. Elements are like the Lego set used to build Earth and the rest of the universe. It’s pretty mind-blowing if you think about it. Everywhere around you are atoms in various combinations that give shape and substance to you and the world around you. A selfie is nothing more than an image of the billions upon billions upon billions of atoms of which you are made (7 billion billion billion, or 7 × 10²⁷, to be exact). Interestingly, just three elements—carbon, hydrogen, and oxygen—make up 99 percent of those atoms of beautiful you.