In my college biology course, I teach a short section on chemistry that's essential to understanding many biological processes. Unfortunately, many of my students grimace when I so much as mention chemistry, due, I suspect, to unhappy experiences with the subject in high school. Undaunted, I plow ahead.
There is a certain romance about chemistry that I strive to communicate to my students, and much of its poetry lies in its building blocks – the elements.
Oxygen, sulfur, gold, tin: For the longest time only 104 of these pure substances were known, 92 of them naturally occurring and 12 man-made. But now the number seems to be unlimited as we engineer ways to create larger and larger atoms, some existing for the briefest of moments before evaporating into the universal ether.
Be that as it may, the elements are jam-packed with the most wonderful lore. All elements have a chemical symbol consisting of one or two letters, frequently taken from their English names: H for hydrogen, He for helium, and B for boron. But some symbols are derived from Latin, Greek, and other languages. The symbol Ag, for silver, is from the Latin word for silver, argentum. In the same manner, we have for gold, Au, from aurum; sodium, Na, from natirum; and one of my favorites, lead, Pb, for plumbum, hence plumbers, who used to work with lead pipe.
But my favorite symbol is the one for the only metallic element that is a liquid at room temperature – mercury, symbol Hg. I have a small vial of mercury that I swirl around for my students. The ancient Romans regarded mercury as a type of silver that flowed. They therefore called it "liquid silver" or hydragyrum, hence its symbol.
But there's an even more alluring name for the stuff, the archaic English "quick-silver." Although quick has come to be synonymous with fast, its original meaning was "living," as if our forebears considered mercury to possess a spirit (hence "the quick and the dead").
The scientist most famously associated with the elements was Dmitri Mendeleev, a pre-Russian Revolution genius born in Siberia and educated in St. Petersburg. In Mendeleev's time, the elements were little more than a grab bag of interesting metals, gases, and liquids.
There was little sense that they could be ordered in any logical way. Mendeleev suspected otherwise. He wrote the elements' symbols down on index cards and began to play a seemingly endless game of solitaire with them. It eventually dawned on him that the elements did, indeed, bear upon one another and could be arranged in groups, or periods, based on shared properties.
For example, sodium, potassium, lithium, and calcium are soft metals that share the exciting ability to explode when placed in water. Helium, xenon, and neon are so-called "noble gases," because they are snobs that will not join with any other element to form a compound.
Mendeleev's ordering of the elements into a periodic table was one of chemistry's great achievements, perhaps its greatest, because it showed that the material world was not a haphazard collection of, in the words of the Wizard of Oz, "clattering ... caliginous junk" but rather had a wondrous rhyme and reason.
When I present the elements to my students, I do it with a hint of reverence. Vial by vial I reveal them: bromine, the only elemental liquid besides mercury; vanadium, one of the hardest of metal elements, used in high-quality cutlery; silicon, neither a metal nor a nonmetal, but something in between (it's shiny and conductive like true metals, but is nonmalleable and shatters under a hammer blow); sulfur, stark yellow and pungent, from the bowels of the earth; and sodium, which cannot bear to be alone and therefore combines, or bonds, with many other elements (such as chlorine, forming salt, NaCl) to achieve stability in a new relationship.
As a fitting coda to my elements lecture, I take my students outside and, at a safe distance, drop a nugget of pure sodium into a coffee can of water. It hisses, smokes, ignites, and then, with a bang, disappears. A cheer goes up. One student exclaims, "I love chemistry!"
That's all I ask.