Some elements are just snobs.
As a math and chemistry tutor at a fancy Boston agency after college, I learned a brand-new vocabulary for talking about elements. To keep my unwilling students focused on the curriculum, an ugly corpus of facts that I’d memorize in pre-session sprints, I would hack away at their boredom with any narrative tool I could find. And so it was that through trial and copious error, I learned to anthropomorphize the un-learnable, to tell living stories about dead things: a positive quadratic parabola makes a smile on graph paper, I told them, because positive exponents are happy. Heated gases take up more space because the heat makes the gas particles angry and they need space to cool off. And so on.
The more absurd the mnemonic, the better it worked. When teaching chemistry, for example, I told them that elements like sodium were “givers,” enthusiastically passing out the “extra” electrons that upset the neat shape of their atoms and thus bonding easily with “takers” like chlorine, whose orbitals must feel incomplete without the givers’ donations. Students rolled their eyes, but some of the same ones found me on Facebook years later to quote these mnemonics back at me, word for word.
Gold, however, is a snob. Most of its fellow transition metals are happy givers, ready to offload as many as five or six electrons at once in pursuit of the shapely, organized orbitals of the noble gases. These odorless, colorless gases are the ultimate snobs, so uninterested in chemical reactions that they were some of the last stable elements in the periodic table to be discovered. In the process of isolating and naming most of the noble gases, William Ramsey called argon “an astonishingly indifferent body” when he bombarded it with reactive chemicals and was unable to provoke a response.
Like gold, noble gases bond only under extreme conditions; gold and palladium were once referred to as the “noble metals.” These details were a lot to remember for teenagers who just wanted to go back to sleep, but the nonsense phrase “gold is a snob” summed up enough of the important facts to earn them a passing grade on a quiz, so it stuck.
(And, of course, gold is expensive and pretty. “Snob” just fits.)
When personification failed to engage students, I reached for historical drama. I’d tell the story of how, on the morning of April 9, 1940, the Nazis seized control of Denmark and two Nobel Prize medals disappeared in the heart of Copenhagen. They had been stashed there by the Danish scientist Niels Bohr on behalf of two German physicists who were enemies of the Third Reich: Max von Laue, a vocal critic of Hitler’s politics, and James Franck, whose Jewish background and academic protests against Nazism had won him an early exile. Because they had entrusted their Nobels to Bohr during the war, they had violated a Nazi prohibition against sending gold out of Germany; the medals’ presence in Bohr’s lab warranted execution for everyone involved.
But the Nazis found no gold medals in Bohr’s laboratory, engraved with the names of traitorous German physicists or otherwise; the institute would eventually be taken over by the Nazis three years later, but Bohr and his associates survived. The SS officers dispatched to find the gold had been looking for solid disks of yellow metal, stashed in a false drawer or above a ceiling tile, but the gold they were looking for was unrecognizable, suspended in an orange solution in a pair of ordinary glass beakers for the duration of the war. When the occupation ended, it was recovered and returned to the laureates in its more conventional form.
The story works for two reasons. For one, even a teenager with an existential fear of science education can’t resist a good scientific caper; for another, any student paying attention would notice that it didn’t make sense. Having absorbed the axiom of gold as a standoffish element, my students were rightfully suspicious of a story in which gold dissolves. After all, while dissolution isn’t exactly bonding, it does require that gold, for once in its miserly life, give something up.
Students who noticed the problem were rewarded, or punished, with an overview of the type of maddeningly complex chemistry elided by my glib personifications. To accurately explain gold’s rare exceptions to stinginess requires a knowledge of chemistry and physics beyond what I’ve ever taught or even formally learned. I drew neat concentric circles in two-dimensional diagrams to explain chemistry to my students, but real electrons orbit nuclei in probabilistic clouds of bizarre three-dimensional shapes, all superimposed on top of one another in a delicate and nearly inscrutable matrix. We draw circular electron-shell diagrams that resemble illustrations of the solar system, another poetic and oversimplified learning tool, and allow the nucleus, the atom’s center, to stand in for the sun.
An accurate representation would be more like a pulsing, three-dimensional sculpture in which planets might or might not be present inside the overlapping zones of probability. But the solar system is still a useful comparison: the electron cloud that would replace Mercury’s flat, circular orbit (in the 3D map of where electrons actually go) would be a single sphere, right around the sun, though few others would be recognizable as “orbits.” Venus would live somewhere inside six pairs of overlapping squashed meatballs at orthogonal orientations, Earth would get four sets of four egg-like clouds each (plus something that looks like one of Venus’s meatball sets positioned on either side of an inexplicable doughnut), and it gets a lot worse from there. As electrons fill these shapes from Mercury outward, they occupy teardrops and doughnuts in pairs, sometimes doubling back to lower levels and sublevels for reasons inexplicable outside of quantum physics.
It’s beautiful and impossible to teach to bored teenagers. And so, a full outer cloud becomes a “happy” cloud, where an outer cloud with lots of empty electron slots will try to attract more or shed all the extras at once; certain numbers of electrons just seem to be better than any numbers in between. I like to think of electrons as the wheels on a vehicle: there’s a clear preference for two or four, and some models do well with eight or eighteen, but five or eleven are problems to be corrected. But because of the crazy shapes of their orbital clouds, electrons in the outer cloud are sometimes, paradoxically, trapped inside an inner cloud. In heavy elements like metals, outlying electrons can be trapped beneath electrons of lower-order clouds, like spare tires nobody knows how to use.
And so, as much as the gold atom’s lonely outer electron would like to leap into another atom’s orbit, leaving a smooth, perfectly filled outer shell behind, it is congenitally, tragically unavailable.
Except when it’s not, of course. My students’ instincts were right: no single acid can effectively dissolve gold. However, a highly corrosive mixture of hydrochloric and nitric acids, in a 3:1 molecular ratio, is capable of eating through glass, gold, and platinum alike. As the Royal Society of Chemistry describes it, the “volatile mixture” of hydrochloric and nitric acids “turns from colourless to a fiery yellow-orange within a few seconds of being prepared,” fuming vigorously to add to its dramatic effect. In a reaction both dramatic and excruciatingly slow, the two acids tag-team the gold: nitric acid tears off electrons to make charged gold ions, which then separate from the rest of the solid metal when they react with the hydrochloric acid.
George de Hevesy, the Hungarian-Jewish chemist who came up with the plan to dissolve the Nobel medals, complained in a letter to von Laue after the war that the process took several hours because the thick, dense gold was “exceedingly unreactive and difficult to dissolve.” De Hevesy went on to win his own Nobel years later and was himself a legendary researcher, but his confidence in the acid mixture’s ability to make the incriminating medals disappear rested on knowledge so ancient that it was closer to magic than to chemistry.
The discovery of the stuff that ate two solid-gold Nobel Prizes and saved a half dozen scientists from Nazi execution predates atomic theory, chemistry, and European science; it belongs to the same worldview that brought us the philosopher’s stone. According to legend, aqua regia (or “king’s water”) was first developed by the eighth-century Iranian alchemist Abu Musa Jabir ibn Hayyan, who is sometimes credited as the first thinker to classify elements according to their behavior. Just as his system, which sorted elements into spirits, metals, and stones, is the ancestor of the periodic table itself, alchemy is the intellectual parent of chemistry and other material sciences. But the difference is more than just the scientific method, especially in their treatment of gold. An esoteric blend of metallurgy, philosophy, and science, alchemical writings survive from an era when gold was an all-consuming religious obsession.
Two of the oldest known fragments of the Hellenic Egyptian alchemists’ wisdom are dated to roughly 300 CE, their authors lost to history; the papyri contain hundreds of recipes for the creation of gold, both real and fake, as well as instructions for producing silver, gemstones, and dyes. Over a thousand years later, the alchemist Eirenaeus Philalethes explained the philosophy behind the long alchemical obsession with gold: “All metallic seed is the seed of gold: for gold is the intention of nature with regard to all metals. If the base metals are not gold, it is only through some accidental hindrance: they are all potentially gold.”
Gold, to alchemists, was less an element with a specific identity than an idealized version of a whole category of substances; it was what all metals were supposed to be.
Alchemists believed metal was as vital as any person or animal. Like modern scientists, these philosophers believed all natural substances, animate and inanimate, should obey the same fundamental principles; like a chemistry tutor in a hurry, they just picked the most poetic rules first and set about proving them right by any means necessary. The English alchemist Thomas Norton wrote in his 1477 book Ordinall of Alkimié, “Metals are generated in the Earth, for above ground they are subject to Rust; hence above ground is the Place of Corruption of Metals and of their gradual Destruction.” From this perspective, the right substances under the right transformations could result in the perfect beauty and longevity that was the natural state of all metals and human beings.
Alchemists used various tests to establish the authenticity of gold, including tests of hardness, malleability, and density; most famously, they used “trial by fire,” in which a metal was examined for traces of oxidation after being exposed to extreme heat. Absent an atomic theory, their results only measured substances according to their characteristics, especially as compared to the idealized behaviors of various materials; if a substance passed the gold tests, it was gold, because there was nothing further to prove.
This poetic arrangement of knowledge made me daydream about teaching AP Alchemy. Alchemists filtered their findings according to their belief that the universe obeyed laws of symbolism, analogies, and mysticism. Every experiment had a religious and philosophical implication on the alchemist; “objectivity” would have been as useless as the concept of an electron. All of that might make a Nobel Prize winner hiss, but, then again, de Hevesy never had to trick a teenager into learning chemistry. Technically, gold is “that element which has 79 protons in its nucleus.” But remembering gold as any soft, nonreactive, dense yellow metal will get you a lot farther in both high school and life; it might even convince you that metal is a subject worth thinking about once you graduate.
The poetry stays with me, too. In later alchemical writings, we find the material world described through a kind of symbolic code, overlapping with literary analogy and elements of Greek astrology. Antoine-Joseph Pernety’s 1758 guide to translating alchemical cryptography, the Dictionnaire mytho-hermétique, used astrological symbols to represent specific experimental processes: Capricorn for fermentation, Cancer for dissolution, Libra for sublimation. Illustrated manuscripts from this era depict epic scenes of nature and astronomy as complex pictorial allegories for chemical processes.
Gold, yellow and eternal, appears as a blazing sun; aqua regia is a green lion devouring it whole.
For alchemists, the vitality of their subject wasn’t just a metaphor; it was the whole point of it all. If you could change the metal by alchemical experimentation, it tantalizingly suggested that human longevity might be similarly mutable, if only the right alchemical process could be found. That aspirational point of view is where chemistry just can’t compete with alchemy. No matter how much evidence stacks up in support of the subatomic world’s infinitesimal structures and jarringly counterintuitive rules, the fundamental laws of chemistry are too foreign to resonate in the same part of our psyche.
Gold has been as central a figure in modern chemistry as any Nobel laureate, for many of the same reasons that made it so beloved to alchemists. It is the star of the Rutherford gold foil experiment, one of the most elegant discoveries in recent scientific history, which established the nuclear model of the atom over competing theories. Each of gold’s therapeutic applications in bioengineering has its own dazzling origin story.
But all of gold’s experimental value pales in comparison to the sheer drama of its impact on the alchemists. For them, gold’s beauty and longevity were not intrinsic characteristics of a metal, but proof of an ideal form to which every metal could aspire and, within a worldview that fused philosophy with science, proof that any substance could reach perfection under the right circumstances. The divorce of alchemy from chemistry is thus as much a tragic loss as it was a necessary step toward establishing a framework of scientific truth. The list of things now forbidden in the realm of scientific thought—subjective experience, moral judgment, mystery, fear, and hope—works just as well as a list of reasons to consume art, religion, and poetry. Gold’s monetary value may be as overblown as ever, but chemistry, for all its one-to-one correspondence with reality, will never be able to fully account for the human bond to the yellow metal.