A dummy’s guide to Mendeleev’s masterpiece
In 1669, Hennig Brand, a German merchant and alchemist, tried a novel experiment he hoped would yield the mythical “philosopher’s stone,” a way to spin base metals into gold. His exact formula is lost to history, but we know he heated urine in a retort, or glass chamber, until the vessel glowed and the dripping liquid burst into flames. Urine, it turned out, wasn’t a source of gold. It was a source of phosphorus, a previously unknown element and the first one isolated in the laboratory. It would take savvier business minds than his to spin the discovery into profits, if not literal gold, but his effort wasn’t wasted. Brand put the glowing extract to work in makeshift lamps he used to read alchemy texts after dark.
So goes the march of science. Two centuries later, in 1869, a Siberian-born genius named Dmitri Mendeleev, inspired by either a dream or a publishing deadline, organized the 63 elements then known into rows and columns according to their weight and chemical properties. (He designated phosphorus as No. 15.) And here was the real stroke of brilliance: He left placeholder boxes for elements where they were expected to exist but had yet to be discovered.
How, you ask, did Mendeleev know what he didn’t know? Simply stated, he arranged all the known elements in order from lightest to heaviest, beginning with hydrogen. He then organized them into seven horizontal rows, or periods, and 18 vertical columns, or groups, whose members have similar physical and chemical properties—like the “alkali metals” in the first group, which are known for their malleability and electrical conductivity. Then, once he’d established clear patterns of properties and behavior, he realized there were gaps in his table, places where there just had to be other elements—and particular kinds of elements, with predictable properties. Never mind that no such substances had ever been found or alchemized—Mendeleev understood that the integrity of his system relied on the existence of those then-missing elements.
The clever Siberian devised his ingenious table before the discovery of electrons, quantum theory, or the 16 radioactive elements created by Glenn Seaborg and others at UC Berkeley. Yet, with some modifications, his shrewd arrangement of elements has endured—unlike, say, Aristotle’s handwavy notion that the world was composed of four elements: earth, water, fire, and air—earning Mendeleev the undisputed title of “father of the periodic table.”
WHY WRITE ABOUT ALL THIS NOW? Well, if you haven’t heard, 2019 is the “International Year of the Periodic Table of Chemical Elements (IYPT 2019)” as proclaimed by the United Nations General Assembly and UNESCO.
Cue the fireworks.
The man in the White House hasn’t tweeted about IYPT 2019, which could help explain why word of the celebration has been slow to penetrate the Twittersphere. Then again, the last time most Americans laid eyes on the periodic table, it was hanging in Walter White’s classroom on Breaking Bad. Most likely you barely noticed it, just as you barely noticed the one from your actual chemistry class. More’s the pity, for as the U.N. puts it, the table is “one of the most significant achievements in science, capturing the essence not only of chemistry, but also of physics and biology.”
Berkeley chemist John Arnold fell under the table’s spell while still a high school student in Lancashire, England. For Arnold, now a professor and undergraduate dean of the College of Chemistry, Mendeleev’s creation has a magic about it. “It really is, I think, one of the greatest scientific accomplishments of all time,” Arnold says. “We can relate things that happen in our lives every day to that one simple, two-dimensional picture.”
Like Arnold, Lee Bernstein, a professor of nuclear engineering who runs the Nuclear Data Group at Berkeley Lab and UC Berkeley, waxes reverent about Mendeleev’s table. “This repeating, this idea that you would reach one end and then start again from the other—it’s brilliant. It’s not just brilliant, though. It’s beautiful. And it’s beautiful, I would say, in the same way the sun rising in the morning is beautiful.”
Bear in mind, Mendeleev’s wasn’t the first periodic table, nor the only one. The German chemist Lothar Meyer, notably, published a similar model just months after Mendeleev. But just as Darwin gets the credit for the theory of evolution—as opposed to his rival, Alfred Russel Wallace—history remembers Mendeleev, not Meyer. That said, Meyer did share a major award with his Russian counterpart for their independent work to establish the periodic law, which states that when the elements are arranged in order of atomic mass, physical and chemical properties will recur periodically.
Arnold calls this phenomenon “the dance of electrons” and speaks of “the magic number eight.” As in eight electrons.
He explains, “There’s a very strong tendency for things to get to the number eight one way or another. One way they can do it is to lose or gain electrons in their valence shell. And you see very clearly on the periodic table that as you start on the left-hand side, there’s a very strong tendency to lose electrons.”
Consider the case, for example, of sodium (Na), way at the far left, and chlorine (Cl) in group 17, one from the right. (Pictured above.)
“Each of those is unhappy,” Arnold says. “One has seven electrons”—speaking here of chlorine’s outer shell, the orbital that determines an atom’s, shall we say, restlessness—“and one has only one. And so they do this deal. They say, ‘OK, I have an electron that I don’t want, and you really want one.’ And you end up with something that’s in the oceans and you can dig it up, and it’s super stable.” The happy result is sodium chloride (NaCl), commonly known as table salt.
“It’s the difference between the electron number an element has and the electron number it would like to have in order to have a stable, noble gas–like configuration,” explains Bernstein. “Mendeleev realized that, for example, the Group 1A elements,” or alkali metals—the leftmost column of the table—“all had very similar properties, they exploded in contact with water or burned combined with the oxygen. He didn’t necessarily know why. But he knew they were all in common in this regard.”
The race to eight is evident even by looking at oxygen, in column 16, just two positions away from neon, poised at the table’s easternmost edge.
“Oxygen wants to be neon,” explains Bernstein, acknowledging the seemingly universal habit of chemists and nuclear scientists to anthropomorphize the elements. “Nature tends to minimize energy. Saying an atom wants to do something is the same as saying there’s an energy release. And the more it wants it, the more energy that’s released.”
So why does oxygen want to be neon?
“Neon is stable. All the elements in this row”—he runs a finger down the right-hand edge of a handcrafted periodic table given to him by a former student—“are stable. They’re noble, they have a low-energy configuration.” In other words, they have a full set of eight valence electrons. “They don’t want to interact.”
The uppermost element in that column is helium, the only element in the top row besides hydrogen. Hydrogen sits alone in the top left corner by dint of its single proton. It, too, is unhappy.
“One is a lonely number,” says Bernstein, “because nature likes to have things in pairs. And so if I get to two protons—helium—it becomes much less chemically reactive. It’s very stable. In fact, it’s kind of snooty. It doesn’t like to play with the other elements. So we call it a noble gas.”
The social life of the elements, it seems, is chemistry, the study of how atoms bond with other atoms to form compounds. And, as Bernstein’s own work demonstrates, Mendeleev’s table is expansive enough to embrace even nuclear physics, the study of how atoms can be blown apart or reconstituted—alchemized, if you like—in the form of new, radioactive elements. We have man-made radioactivity to thank for luminous watch dials, PET scans, and radiotherapy, and to curse for nuclear weapons. (When it comes to nuclear energy, it seems, thanking and cursing are both popular options.)
Sharing electrons in their outer shells is how elements bond with their neighbors. Should their number of protons change, they actually become their neighbors. Unlike electrons, protons reside with neutrons inside the atom’s nucleus, the province not of chemistry but nuclear physics. Picture electrons as planets, orbiting a sun—the nucleus.
The particle accelerator invented by Ernest O. Lawrence, namesake of the Livermore and Berkeley labs, enabled his colleagues and academic descendants to create strange new elements by restructuring atoms themselves. This chapter in tabular history began in 1937 with technetium, which Mendeleev hadn’t identified but anticipated as element 43. Mendeleev even anticipated the heavy, radioactive elements that have extended the number of known elements far beyond the 88 found in nature. (Some sources argue for 92 or 94, but many nuclear scientists—Bernstein among them—don’t credit radioactive elements with half-lives so short that they’re more naturally absent than present.) Sixteen of these so-called transuranic elements, including berkelium, californium, lawrencium, and seaborgium, were discovered (and, you probably guessed it, named) by Berkeley scientists. (Read more about berkelium here.)
It’s Seaborg, not coincidentally, who’s responsible for the two breakaway rows found in modern renditions of Mendeleev’s table. These are the lanthanides and the actinides, which mathematically bridge barium (56) and hafnium (72) in Row 6 and radium (88) and rutherfordium (104) in Row 7, respectively. Suffice it to say this gets us into the realm of quantum mechanics and the discovery of orbital shapes. More in-depth exploration of the table’s nether regions is discouraged without rubber gloves and safety goggles.
The point, as we celebrate IYPT 2019, is that the periodic table accommodates even those elements Mendeleev could never have imagined, ones created only by smashing atoms at incomprehensible speeds with subatomic particles from a machine that didn’t exist until decades after his death. The total of known elements is currently 118, but there are apt to be more to come.
“I’m sure we’ll discover new elements,” Arnold says, “119, 120 are on people’s radar in Russia and in the U.S., and probably Japan as well. Given enough time and effort, we’ll get there.”
And whatever new elements turn up, they’ll all have a place at Mendeleev’s table, notwithstanding some inevitable griping over where, exactly, to seat them.
“It’s just an amazing, amazing thing that too many people take for granted,” says Arnold. “There’s very little like it scientifically that I can think of. E=mc2, I guess, pretty much everybody knows because it’s easy and quick, and once you’ve heard it, it’s hard to forget. The periodic table is sort of like that. It’s very memelike, it’s become a part of everything, in a way. It is everything, which is probably why.”
And so, with that in mind, let’s tip a vessel of Russian vodka to 150 years of the periodic table, fire up Tom Lehrer’s “The Elements” on the karaoke machine, and party like it’s 1869.
Noble-gas types are urged to keep to your snooty selves, lest you kill the buzz for the rest of us.
Barry Bergman has a special place in his heart for The Elements of Style. He is married to an actual science journalist.