The complex building block of matter beyond the atom is the molecule. There are 90 odd elements. But this number is hardly enough to provide enough variety. It is good to have rice and flower and sugar, salt and butter and a range of spices. However, when they are combined in the right proportions under the right conditions, many wondrous culinary creations can emerge.
Likewise, there is a cosmic culinary complex, as it were, by which nature, always in accordance with established principles, concocts an incredible richness in atomic combinations. These are the molecules of compounds. They are at the root of much of the variety in perceived reality. All the substances we see around, and the multitude that we don’t see, are ultimately made up of molecules containing two or more atoms.
There may be just two or three atoms, or they may number a few hundred. Even two or three can be significant. The molecule of common salt is made up of just two kinds of atoms, the water molecule has no more than three atoms, and we know how important and indispensable they are. As all of us know, mere sodium or chlorine is no good. But in combination, they make the soup tasty. No amount of hydrogen and oxygen, just by themselves, can sustain life. But when combined in the right proportion, they form water.
Molecules are imperceptibly small. A molecule of an ordinary substance barely stretches to a few millionths of a millimeter. One of the intellectual achievements of 19th-century science was to reckon how many molecules there are in, say, a teaspoon of water. This is of the order of a trillion trillion. We simply cannot grasp what this number is. Written out explicitly, it is 1 followed by 24 zeroes. There are more molecules in a cup of water than there are stars in the entire universe.
It is difficult to form an idea of this numerical monstrosity at the root of perceived reality by drinking a glass of water or by tasting salt. That we are able to arrive at such a number from conceptual considerations is an indication of the power of the human mind. The number of molecules in two grams of hydrogen, known as Avogadro’s number, is probably the first number of such mind-boggling magnitude ever to cross the human mind in a non-speculative context. Already in the 19th century, a simple and clever experiment enabled physicists to estimate how many molecules there are in a drop of oil. Such a drop, thrown into a tank of water, can spread all over the 30-square-foot surface of an entire tank. Taking the radius of the drop to be of the order of a millimeter, one can estimate the size of the molecules that spread as a single layer over this whole area.
Next, consider the very interesting molecule made up of six carbon atoms and six hydrogen ones, forming what chemists describe as a ring. This is the molecule of benzene, a toxic liquid that can catch fire at the slightest provocation. An incessant eerie switching goes on among the chemical bonds in the ring. This miniature ring is the cornerstone in a great many more complex molecules that affect the olfactory cells in mucous membranes in the nose. Put in plain language, we can smell them. So benzene-based substances are called aromatic compounds, though these are not the only ones with this property. This is another marvel in the physical world: The root of the perceived reality of smell is to be seen in molecules that lock in mostly carbon and hydrogen atoms in strongly linked rings!
Then there are macromolecules—an oxymoron in scientific jargon because “macro” means big, and molecule means small mass. They are so named because, compared with the molecules of ordinary substances, these are larger by far, by an order of 100 times.
Macromolecules are like trains, molecules linked to molecules, in chains or in more complex structures. Sometimes all the wagons in a train are the same. We get additional polymers this way: a whole series of identical molecules hooked together like beads in a rosary thread. Polystyrene—the stuff of which disposable cups and packing cushions are made—consists of such identical molecules. On the other hand, if the component units are not quite the same, we get a condensation polymer. These are polyester materials we see everywhere these days. All our plastics are polymers.
Long before human ingenuity learned to produce polymers, nature has been doing it on grander scales. Rubber and cellulose with their peculiar properties are polymers par excellence. Polymers also come into play in living matter. Proteins, which form the material basis for life, are polymers. Science has unraveled polymers in much of life.
Human beings try to go a step beyond nature’s handiwork, often along different directions. So, for example, we have made buckyballs, molecules made up of 60 or more carbon atoms. These have the tremendously useful property that, in association with ions of thallium and rubidium, they become superconducting at reasonably high temperature. More formally known as fullerene, these molecules are finding their way into the world of applied science in a variety of ways: producing super-strong fibers, and other materials for medicinal purposes.
Analyzing starlight with spectroscopes, astronomers have recognized telltale signs of large aromatic molecules, the so-called polycyclic aromatic hydrocarbons—fragrance in the firmament, one might say, because these are made up of benzene rings.
Deoxyribonucleic acids or DNA are stupendously large molecules, nearly 120 million times as massive as a hydrogen atom. With variations here and there, they get intertwined in pairs, twisting away in spiral forms, often with some 5,000 turns, forming a characteristic structure that has come to be called the “double helix.” These awesome complex spirals are the most precious entities in the entire universe, for in them are encoded every bit of information pertaining to the functioning and continuation of the life principle. The combined mass of all the DNA molecules on earth is pitifully small compared with the mass of the ocean water, but they are like the libraries of the world: in them are hidden all the knowledge and information that keeps the earth throbbing with life. DNA molecules are made up of four different kinds of more basic molecules, the so-called nucleotides. Every human cell is made up of some 25,000 of these.
Ultimately, protons and electrons make the atoms about some elements, and atoms make the molecules that spell out a splendor in the rich variety of matter and life in the world. Recall the lines of Alexander Pope who wrote long before scientists thought of atoms and molecules:
See plastic Nature working to this end,
The single atoms each to the other tend,
Attract, attracted to, the next in place,
Form’d and impell’d its neighbor to embrace.