Very recently, a milestone was reached, an important goal in the study of chemistry. The seventh row of the periodic table was officially filled in. Now, almost nobody outside of a few laboratories cares anything about oganesson and tennessine (nice to see that my state finally gets its own element, though), and they’ll probably never have any actual use, but they’re there, and now we know they are.
Especially in science fiction, there’s the trope of the “unknown” element that has or allows some sort of superpowers. In some cases, this takes the form of a supposed chemical element, such as the fictitious “elerium”, “adamantium”, or even “unobtainium”. Other works instead use something that could better be described as a compound (“kryptonite”) or something else entirely (“element zero”). But the idea remains the same.
So this post is a quick overview of the elements we know. As a whole, science is quite confident that we do know all the elements in nature. Atomic theory is pretty clear on that point; the periodic table has no more “gaps” in the middle, and we’ve now filled in all the ones at the end. But element 118 only got named in 2016, and that’s proof that we didn’t always know everything.
The classical idea of “element” wasn’t exactly chemically sound. We know the Greek division of earth, air, fire, and water, a four-way distinction still used in fantasy literature and other media; other cultures had similar concepts, if not always the same divisions.
But they also knew of chemical elements, particularly a few that occur naturally in “pure” form. Gold, silver, copper, tin, and lead are the ones most people recognize as being “prehistoric”. (Native copper is relatively rare, but it pops up in a few places, and most of those, coincidentally enough, show evidence of a bronze-working culture nearby.) Carbon, in the form of charcoal, doesn’t take too much work to purify. Meteorites provided early iron. Sulfur can be found anywhere there’s a volcano—probably a good reason to associate the smell of “brimstone” with eternal punishment. And don’t forget “quicksilver”, or mercury.
We’ve also got evidence of bismuth and antimony known in something like elemental form. Both found medicinal uses, despite being quite toxic. (Mercury was the same, and it’s even worse, because it’s a liquid at room temperature.) And then there’s the curious case of platinum. Some evidence points to it being used on either side of the Atlantic in olden times, which is good news for the fantasy types who need a coin more valuable than gold.
For most of Western history, chemists—or what passed for them—tended to focus on compounds rather than isolating elements. However, there were a few advances on that front, too. Albertus Magnus separated arsenic from its compounding partners in the 13th century, much to the delight of poisoners everywhere. Elemental zinc is also an alchemical discovery in Europe, though a few records point to it being made far earlier in India.
Around this time, the very definition of an element was in flux, especially in medieval and Renaissance Europe. You still had the Aristotelian view of the four elements, broadly supported by the Church, but then there were the alchemists and others working on their own things. Some of the questions they considered led to great discoveries later on, but the technology wasn’t yet ready to isolate all the elements. So, in this particular age (conveniently enough, the perfect era for fantasy), there’s still a lot left to find.
The enlightened ones
Henning Brand gets the credit for discovering phosphorus, according to the book I’m looking at right now. That was in 1669, almost a century and a half after Paracelsus possibly experimented with metallic zinc, and a full four hundred years after the last definitive evidence for discovery. The next on the timeline doesn’t come until 1735: cobalt.
Those opened the floodgates. By this point, you could hear the first stirrings of the Industrial Revolution, and that brought advances to the technology of chemistry. The more liberal academic climate led to greater experimentation, as well. All in all, the late 18th century was the beginning of an element storm. Thanks to electricity, the vacuum, and numerous other developments, enterprising chemists (no longer alchemists at this point) started finding elements seemingly everywhere.
It’s this era where the periodic table is a bit of a Wild West. Everything is up in the air, and nobody really knows what’s what. Indeed, there are quite a few mistaken discoveries in the years before Mendeleev, some of them even finding their way into actual chemistry textbooks. In most cases, these were simple mistakes or even rediscoveries; there were a few fights over primacy, too. But it shows that it wasn’t until relatively recently that we knew all these elements couldn’t exist.
The periodic age
Once the periodic table became the gold standard for chemistry, finding new elements became a matter of filling in the blanks. We know there’s an element that goes here, and it’ll be a little like these. So that’s how we got most of the rest of the gang in the late 1800s through about 1940 or so.
Ever since nuclear science came into existence, we’ve seen a steady stream of new elements being created in particle accelerators or other laboratory conditions. Strictly speaking, that began in 1937 with technetium (more on it in a moment), but it really got going after World War II. Over the next 70 years, scientists made from scratch a couple dozen new elements, none of which exist in nature, most tearing themselves apart within the barest fraction of a second.
Nuclear physics explains why these superheavy elements don’t work right. The way we make them is by forcing lighter elements to fuse, but that leaves them with too few neutrons to truly be stable. The island of stability hypothesis says that some of them could actually be stable enough to be useful…if we built them right. So, even though there’s no more room on the periodic table (unless Period 8 turns out to exist), that’s not to say all those spots along the bottom row have to disappear in the blink of an eye.
Last but not least, there are a few weirdos in the periodic table, and these deserve special mention. Two of them are quite odd indeed: technetium and promethium. By any reasonable standard, these should be stable. Technetium is element 43, a transition metal that should act a bit like a heavier manganese.
No such luck. Due to a curious quirk in atomic structure, 43 is a kind of “magic number”. An atom with 43 protons (which would be, by definition, technetium) can never be fully stable. At best, it can have a long half-life, and some isotopes do last for tens of thousands of years, but stable? Alas, no. Promethium, element 61, is the same way, for much the same reason.
Uranium is well-known as the last “stable” element, although none of its isotopes are truly stable; the most stable, 238, has a half-life around the current age of the Earth. Element 92 is also familiar as the fuel for a man-made fission reactor or a bomb, but it’s even more interesting than that. Because it’s radioactive, yet it can last for so long, uranium has the curious property of “spontaneous” fission. A few places in the world are actually natural nuclear reactors, though most have long since decayed below critical mass. A culture living near something like that, however, might discover neptunium, plutonium, and other decay byproducts long before they probably should. (They’ll likely find the link between radiation and cancer pretty early, too.)
Depending on who you ask, we’re either at the end of the periodic table, or we’re not. Some theories have it running out at 118, some say 137, and one even says infinity. The patterns are already clear, though. If there’s no true island of stability, then most anything else we find is going to be extremely short-lived, highly radioactive, or both. Probably that last one.
Today, then, there’s not really the possibility for an “undiscovered” element. We simply don’t have a place to put it. That doesn’t mean your sci-fi is out of luck, though. There could be isotopes of existing elements that we don’t have; this is especially true of the transuranic elements. More likely, though, would be a compound not seen on Earth. A crystal structure we don’t have, or an alloy, or something of that sort—a novel combination of existing elements, rather than a single new one.
And then you have the more bizarre forms of matter. Neutronium (the stuff of neutron stars), if you could make it stable when you don’t have an Earth mass of the stuff packed into something the size of your house, would be a true “element zero”, and it may have interesting properties. Antimatter atoms would annihilate their “normal” cousins, but we don’t know much about them other than that. You might even be able to handwave something using other particles, like muons, or different arrangements of quarks. These wouldn’t create new elements in the traditional sense, but an entire new branch of chemistry.
So don’t get discouraged. Just because there’s no place on the periodic table to put your imaginary elements, that doesn’t mean you have to choose between them and scientific rigor. You just have to think outside the 118 boxes.