Surveys reveal that only 50 percent of people questioned know that the Earth goes around the sun once a year, and only 40 percent realize that electrons are smaller than atoms. That’s sad enough, but it is frightening that a mere 10 percent of the population understands what a molecule is. This is distressing, because everything in the physical world depends upon molecular action.
Molecules are the fundamental components of matter. They are made up of atoms, which in turn are composed of even smaller particles called protons, neutrons, and electrons. Perhaps it isn’t really surprising that people have misconceptions about molecules, since molecules are almost inconceivably small, roughly 100,000 water molecules could fit across the width of a single human hair. Nobody had seen a molecule until 2009 when using ultra-sophisticated atomic force microscopy scientists were able to take a picture of a molecule called pentacene that was clearly revealed to be composed of five fused benzene rings.
So, how did scientists conclude that the world was made of invisible molecules? The simplest answer may be that our ideas about molecules must be correct because we can predict and explain the behavior of matter based on the concept that everything is made up of molecules which in turn are composed of atoms joined together in specific ways. Of course, it took many, many years for the concept to evolve. As early as the 5th century BCE the Greek philosopher Leucippus and his student Democritus had suggested that if matter were cut into smaller and smaller pieces, eventually you would arrive at a particle that could not be divided further. For this they coined the term, “atom” from the Greek for “indivisible.” They envisioned different forms of matter to be made of atoms that differed in shapes and sizes.
Interestingly, this idea lay dormant for two thousand years until Robert Boyle in his classic work, “The Skeptical Chymist” described matter as being made of various “corpuscles” of different sorts and sizes that could be rearranged to form new substances. Antoine Lavoisier then recognized these corpuscles as “elements” from which all matter is made, and in his 1789 book “The Elements of Chemistry” described how during a chemical reaction, the total mass of the reactants is equal to the total mass of the products. John Dalton then rationalized this observation by claiming that in a chemical reaction atoms are not lost or gained but just rearrange and hook together to form novel entities for which Amadeo Avogadro coined the term “molecule” from the Latin “moles” meaning “a small mass.”
By making careful observations of chemical reactions, August Kekule concluded that atoms have a characteristic number of “hooks” that they can use to join together, and that the carbon atom has four such hooks which came to be called “bonds.” Then in 1874, August von Hofmann built the first ever model of a molecule using balls to represent atoms and sticks for bonds. His model of methane was a planar structure with a carbon atom joined to four hydrogen atoms. This was refined by van’t Hoff who concluded that molecules are three dimensional and the carbon in methane is at the center of a tetrahedron with the hydrogens at the four corners. Amazingly, all of this was done by inference based on what must be happening at the atomic level to explain reactions that could be observed in the lab. Today there are various instrumental methods such as x-ray crystallography and nuclear magnetic resonance spectroscopy that can identify molecular structures even as complex as DNA.
We chemists spend our lives thinking about, and working with, molecules. That’s why we become so irritated when we are confronted with molecular nonsense. Like the statement made by a meteorologist to the effect that fog is saturated air, and as the air cools, the water molecules get bigger and bigger until they become visible. Water molecules do not change in size. They can cluster and form a liquid or separate and form a vapor. Fog does not consist of large water molecules; it consists of water molecules that have clustered to form droplets of liquid.
Many “wellness influencers” have repeated the absurd claim that “margarine is about one molecule away from plastic.” Plastics are composed polymers while margarine is a blend of fats and water. There is no chemical similarity between the two. In any case, being “one molecule away” is a totally meaningless expression. Substances are made of molecules, which in turn are composed of atoms joined together is a specific pattern. I suppose one might say that hydrogen peroxide, H2O2, is one atom away from water, H2O, but even this is meaningless. That extra oxygen atom changes the properties of the substance dramatically. Sticking a finger into a bottle of pure hydrogen peroxide quickly reveals the effect of that extra oxygen. Just as outrageous is the claim made for the “Laundry Disk,” a product that is supposed to enable us to wash our clothes without detergent. Its makers say that it contains “an activated ceramic that makes water molecules smaller and enhances their ability to penetrate the fabric.” The Laundry Disk does not work this way, or indeed in any other way.
Water molecules do not change in size, but they do allow other molecules to squeeze between them. This is why water is such an excellent solvent. Have you ever wondered where sugar goes when you dissolve it in a glass of water? Another interesting molecule demonstration involves a phenomenon that was first noted by the ancient Greeks. If we combine equal amounts of water and alcohol, then we get a volume that is less than the sum of the two. How come? The only possible answer is that the alcohol molecules have lodged themselves in the spaces between the water molecules. And what can you do with that mixture of water and alcohol? Drink a toast to the molecule!
