by Sam Kean
That breakdown could set limits on the periodic table. To return to the electron-planet analogy, just as Mercury zips around the sun every three months while Neptune drags on for 165 years, inner electrons orbit much more quickly around a nucleus than electrons in outer shells. The exact speed depends on the ratio between the number of protons present and alpha, the fine structure constant discussed last chapter. As that ratio gets closer and closer to one, electrons fly closer and closer to the speed of light. But remember that alpha is (we think) fixed at 1/137 or so. Beyond 137 protons, the inner electrons would seem to be going faster than the speed of light—which, according to Einstein’s relativity theory, can never happen.
This hypothetically last element, 137, is often called “feynmanium,” after Richard Feynman, the physicist who first noticed this pickle. He’s also the one who called alpha “one of the great damn mysteries of the universe,” and now you can see why. As the irresistible force of quantum mechanics meets the immovable object of relativity just past feynmanium, something has to give. No one knows what.
Some physicists, the kind of people who think seriously about time travel, think that relativity may have a loophole that allows special (and, conveniently, unobservable) particles called tachyons to go faster than light’s 186,000 miles per second. The catch with tachyons is that they may move backward in time. So if super-chemists someday create feynmanium-plus-one, un·tri·octium, would its inner electrons become time travelers while the rest of the atom sits pat? Probably not. Probably the speed of light simply puts a hard cap on the size of atoms, which would obliterate those fanciful islands of stability as thoroughly as A-bomb tests did coral atolls in the 1950s.
So does that mean the periodic table will be kaput soon? Fixed and frozen, a fossil?
No, no, and no again.
* * *
If aliens ever land and park here, there’s no guarantee we’ll be able to communicate with them, even going beyond the obvious fact they won’t speak “Earth.” They might use pheromones or pulses of light instead of sounds; they might also be, especially on the off off chance they’re not made of carbon, poisonous to be around. Even if we do break into their minds, our primary concerns—love, gods, respect, family, money, peace—may not register with them. About the only things we can drop in front of them and be sure they’ll grasp are numbers like pi and the periodic table.
Of course, that should be the properties of the periodic table, since the standard castles-with-turrets look of our table, though chiseled into the back of every extant chemistry book, is just one possible arrangement of elements. Many of our grandfathers grew up with quite a different table, one just eight columns wide all the way down. It looked more like a calendar, with all the rows of the transition metals triangled off into half boxes, like those unfortunate 30s and 31s in awkwardly arranged months. Even more dubiously, a few people shoved the lanthanides into the main body of the table, creating a crowded mess.
No one thought to give the transition metals a little more space until Glenn Seaborg and his colleagues at (wait for it) the University of California at Berkeley made over the entire periodic table between the late 1930s and early 1960s. It wasn’t just that they added elements. They also realized that elements like actinium didn’t fit into the scheme they’d grown up with. Again, it sounds odd to say, but chemists before this didn’t take periodicity seriously enough. They thought the lanthanides and their annoying chemistry were exceptions to the normal periodic table rules—that no elements below the lanthanides would ever bury electrons and deviate from transition-metal chemistry in the same way. But the lanthanide chemistry does repeat. It has to: that’s the categorical imperative of chemistry, the property of elements the aliens would recognize. And they’d recognize as surely as Seaborg did that the elements diverge into something new and strange right after actinium, element eighty-nine.
Actinium was the key element in giving the modern periodic table its shape, since Seaborg and his colleagues decided to cleave all the heavy elements known at the time—now called the actinides, after their first brother—and cordon them off at the bottom of the table. As long as they were moving those elements, they decided to give the transition metals more elbow room, too, and instead of cramming them into triangles, they added ten columns to the table. This blueprint made so much sense that many people copied Seaborg. It took a while for the hard-liners who preferred the old table to die off, but in the 1970s the periodic calendar finally shifted to become the periodic castle, the bulwark of modern chemistry.
But who says that’s the ideal shape? The columnar form has dominated since Mendeleev’s day, but Mendeleev himself designed thirty different periodic tables, and by the 1970s scientists had designed more than seven hundred variations. Some chemists like to snap off the turret on one side and attach it to the other, so the periodic table looks like an awkward staircase. Others fuss with hydrogen and helium, dropping them into different columns to emphasize that those two non-octet elements get themselves into strange situations chemically.
Really, though, once you start playing around with the periodic table’s form, there’s no reason to limit yourself to rectilinear shapes.* One clever modern periodic table looks like a honeycomb, with each hexagonal box spiraling outward in wider and wider arms from the hydrogen core. Astronomers and astrophysicists might like the version where a hydrogen “sun” sits at the center of the table, and all the other elements orbit it like planets with moons. Biologists have mapped the periodic table onto helixes, like our DNA, and geeks have sketched out periodic tables where rows and columns double back on themselves and wrap around the paper like the board game Parcheesi. Someone even holds a U.S. patent (#6361324) for a pyramidal Rubik’s Cube toy whose twistable faces contain elements.
Musically inclined people have graphed elements onto musical staffs, and our old friend William Crookes, the spiritualist seeker, designed two fittingly fanciful periodic tables, one that looked like a lute and another like a pretzel. My own favorite tables are a pyramid-shaped one—which very sensibly gets wider row by row and demonstrates graphically where new orbitals arise and how many more elements fit themselves into the overall system—and a cutout one with twists in the middle, which I can’t quite figure out but enjoy because it looks like a Möbius strip.
We don’t even have to limit periodic tables to two dimensions anymore. The negatively charged antiprotons that Segrè discovered in 1955 pair very nicely with antielectrons (i.e., positrons) to form anti-hydrogen atoms. In theory, every other anti-element on the anti–periodic table might exist, too. And beyond just that looking-glass version of the regular periodic table, chemists are exploring new forms of matter that could multiply the number of known “elements” into the hundreds if not thousands.
First are superatoms. These clusters—between eight and one hundred atoms of one element—have the eerie ability to mimic single atoms of different elements. For instance, thirteen aluminium atoms grouped together in the right way do a killer bromine: the two entities are indistinguishable in chemical reactions. This happens despite the cluster being thirteen times larger than a single bromine atom and despite aluminium being nothing like the lacrimatory poison-gas staple. Other combinations of aluminium can mimic noble gases, semiconductors, bone materials like calcium, or elements from pretty much any other region of the periodic table.
The clusters work like this. The atoms arrange themselves into a three-dimensional polyhedron, and each atom in it mimics a proton or neutron in a collective nucleus. The caveat is that electrons can flow around inside this soft nucleic blob, and the atoms share the electrons collectively. Scientists wryly call this state of matter “jellium.” Depending on the shape of the polyhedron and the number of corners and edges, the jellium will have more or fewer electrons to farm out and react with other atoms. If it has seven, it acts like bromine or a halogen. If four, it acts like silicon or a semiconductor. Sodium atoms can also become jellium and mimic other elements. And there’s no
reason to think that still other elements cannot imitate other elements, or even all the elements imitate all the other elements—an utterly Borgesian mess. These discoveries are forcing scientists to construct parallel periodic tables to classify all the new species, tables that, like transparencies in an anatomy textbook, must be layered on top of the periodic skeleton.
Weird as jellium is, the clusters at least resemble normal atoms. Not so with the second way of adding depth to the periodic table. A quantum dot is a sort of holographic, virtual atom that nonetheless obeys the rules of quantum mechanics. Different elements can make quantum dots, but one of the best is indium. It’s a silvery metal, a relative of aluminium, and lives just on the borderland between metals and semiconductors.
Scientists start construction of a quantum dot by building a tiny Devils Tower, barely visible to the eye. Like geologic strata, this tower consists of layers—from the bottom up, there’s a semiconductor, a thin layer of an insulator (a ceramic), indium, a thicker layer of a ceramic, and a cap of metal on top. A positive charge is applied to the metal cap, which attracts electrons. They race upward until they reach the insulator, which they cannot flow through. However, if the insulator is thin enough, an electron—which at its fundamental level is just a wave—can pull some voodoo quantum mechanical stuff and “tunnel” through to the indium.
At this point, scientists snap off the voltage, trapping the orphan electron. Indium happens to be good at letting electrons flow around between atoms, but not so good that an electron disappears inside the layer. The electron sort of hovers instead, mobile but discrete, and if the indium layer is thin enough and narrow enough, the thousand or so indium atoms band together and act like one collective atom, all of them sharing the trapped electron. It’s a superorganism. Put two or more electrons in the quantum dot, and they’ll take on opposite spins inside the indium and separate in oversized orbitals and shells. It’s hard to overstate how weird this is, like getting the giant atoms of the Bose-Einstein condensate but without all the fuss of cooling things down to billionths of a degree above absolute zero. And it isn’t an idle exercise: the dots show enormous potential for next-generation “quantum computers,” because scientists can control, and therefore perform calculations with, individual electrons, a much faster and cleaner procedure than channeling billions of electrons through semiconductors in Jack Kilby’s fifty-year-old integrated circuits.
Nor will the periodic table be the same after quantum dots. Because the dots, also called pancake atoms, are so flat, the electron shells are different than usual. In fact, so far the pancake periodic table looks quite different than the periodic table we’re used to. It’s narrower, for one thing, since the octet rule doesn’t hold. Electrons fill up shells more quickly, and nonreactive noble gases are separated by fewer elements. That doesn’t stop other, more reactive quantum dots from sharing electrons and bonding with other nearby quantum dots to form… well, who knows what the hell they are. Unlike with superatoms, there aren’t any real-world elements that form tidy analogues to quantum-dot “elements.”
In the end, though, there’s little doubt that Seaborg’s table of rows and turrets, with the lanthanides and actinides like moats along the bottom, will dominate chemistry classes for generations to come. It’s a good combination of easy to make and easy to learn. But it’s a shame more textbook publishers don’t balance Seaborg’s table, which appears inside the front cover of every chemistry book, with a few of the more suggestive periodic table arrangements inside the back cover: 3D shapes that pop and buckle on the page and that bend far-distant elements near each other, sparking some link in the imagination when you finally see them side by side. I wish very much that I could donate $1,000 to some nonprofit group to support tinkering with wild new periodic tables based on whatever organizing principles people can imagine. The current periodic table has served us well so far, but reenvisioning and recreating it is important for humans (some of us, at least). Moreover, if aliens ever do descend, I want them to be impressed with our ingenuity. And maybe, just maybe, for them to see some shape they recognize among our collection.
Then again, maybe our good old boxy array of rows and turrets, and its marvelous, clean simplicity, will grab them. And maybe, despite all their alternative arrangements of elements, and despite all they know about superatoms and quantum dots, they’ll see something new in this table. Maybe as we explain how to read the table on all its different levels, they’ll whistle (or whatever) in real admiration—staggered at all we human beings have managed to pack into our periodic table of the elements.
ACKNOWLEDGMENTS AND THANKS
I would first like to thank my dear ones. My parents, who got me writing, and never asked too often what exactly I was going to do with myself once I’d started. My lovely Paula, who held my hand. My siblings, Ben and Becca, who taught me mischief. All my other friends and family from South Dakota and around the country, who supported me and got me out of the house. And finally my various teachers and professors, who first related many of the stories here, without realizing they were doing something so valuable.
I would furthermore like to thank my agent, Rick Broadhead, who believed that this project was a swell idea and that I was the one to write it. I owe a lot as well to my editor at Little, Brown, John Parsley, who saw what this book could be and helped shape it. Also invaluable were others at and around Little, Brown, including Cara Eisenpress, Sarah Murphy, Peggy Freudenthal, Barbara Jatkola, and many unnamed others who helped design and improve this book.
I offer thanks, too, to the many, many people who contributed to individual chapters and passages, either by fleshing out stories, helping me hunt down information, or offering their time to explain something to me. These include Stefan Fajans; Theodore Gray of www.periodictable.com; Barbara Stewart at Alcoa; Jim Marshall of the University of North Texas; Eric Scerri of the University of California at Los Angeles; Chris Reed at the University of California, Riverside; Nadia Izakson; the communications team at Chemical Abstracts Service; and the staff and science reference librarians at the Library of Congress. If I’ve left anyone off this list, my apologies. I remain thankful, if embarrassed.
Finally, I owe a special debt of gratitude to Dmitri Mendeleev, Julius Lother Meyer, John Newlands, Alexandre-Emile Béguyer de Chancourtois, William Odling, Gustavus Hinrichs, and the other scientists who developed the periodic table—as well as thousands of other scientists who contributed to these fascinating stories about the elements.
NOTES AND ERRATA
Introduction
“literature, poison forensics, and psychology”: Another topic I learned about via mercury was meteorology. The final peal of the death knell of alchemy sounded on the day after Christmas in 1759, when two Russian scientists, trying to see how cold they could get a mixture of snow and acid, accidentally froze the quicksilver in their thermometer. This was the first recorded case of solid Hg, and with that evidence, the alchemists’ immortal fluid was banished to the realm of normal matter.
Lately mercury has been politicized as well, as activists in the United States have campaigned vigorously against the (totally unfounded) dangers of mercury in vaccines.
1. Geography Is Destiny
“anything but a pure element”: Two scientists observed the first evidence for helium (an unknown spectral line, in the yellow range) during an eclipse in 1868—hence the element’s name, from helios, Greek for “sun.” The element was not isolated on earth until 1895, through the careful isolation of helium from rocks. (For more on this, see chapter 17.) For eight years, helium was thought to exist on earth in minute quantities only, until miners found a huge underground cache in Kansas in 1903. They had tried to light the gas shooting out of a vent in the ground on fire, but it wouldn’t catch.
“only the electrons matter”: To reiterate the point about atoms being mostly empty space, Allan Blackman, a chemist at the University of Otago in New Zealand, wrote in the January 28, 2008, Otago Daily Times: “Consider the mo
st dense known element, iridium; a sample of this the size of a tennis ball would weigh just over 3 kilograms [6.6 pounds]…. Let’s assume that we could somehow pack the iridium nuclei together as tight as we possibly could, thereby eliminating most of that empty space…. A tennis ball–sized sample of this compacted material would now weigh an astonishing seven trillion tonnes [7.7 trillion U.S. tons].”
As a footnote to this footnote, no one really knows whether iridium is the densest element. Its density is so close to osmium’s that scientists cannot distinguish between them, and in the past few decades they’ve traded places as king of the mountain. Osmium is on top at the moment.
“every quibbling error”: For more detailed portraits of Lewis and Nernst (and many other characters, such as Linus Pauling and Fritz Haber), I highly recommend Cathedrals of Science: The Personalities and Rivalries That Made Modern Chemistry by Patrick Coffey. It’s a personality-driven account of the most important era in modern chemistry, between about 1890 and 1930.
“most colorful history on the periodic table”:Other facts about antimony:
1. Much of our knowledge of alchemy and antimony comes from a 1604 book, The Triumphal Chariot of Antimony, written by Johann Thölde. To give his book a publicity boost, Thölde claimed he’d merely translated it from a 1450 text written by a monk, Basilius Valentinus. Fearing persecution for his beliefs, Valentinus had supposedly hidden the text in a pillar in his monastery. It remained hidden until a “miraculous thunderbolt” split the pillar in Thölde’s time and allowed him to discover the manuscript.
2. Although many did call antimony a hermaphrodite, others insisted it was the essence of femininity—so much so that the alchemical symbol for antimony, , became the general symbol for “female.”