Are there Undiscovered Elements Beyond The Periodic Table?

Adamantium, bolognium, dilithium. Element Zero, Kryptonite. Mithril, Netherite, Orichalcum, Unobtanium. We love the idea of ​​fictional items with miraculous properties that science has not yet discovered. But is it really possible that new

elements

exist beyond the

periodic

table

? Science fiction in particular often imagines artificial or yet-to-be discovered

elements

whose incredible properties will propel us into our stellar future. But to anyone who has studied a little chemistry, this seems far-fetched. The elements of the

periodic

table

are defined by the number of protons in the atomic nucleus (the atomic number), so how can there be room for new elements?

Sure, we could keep adding protons to the high end of the periodic table, but they seem hopelessly unstable and therefore of little use for building warp engines. But the fact is that there were gaps in the periodic table: atomic numbers that seemed to appear naturally. And it may also be that the current upper end of the periodic table is simply another such gap, beyond which there may exist an island of stability containing useful elements never before found. To understand the possibility of new artificial elements, let's start with the history of the first artificial element. We start from the moment Mendelev discovered the periodic table.

He arranged the known elements according to their atomic weight and noted periodic recurrences of chemical properties as atomic weight increased. We now know that chemical properties depend on the number of valence or outer shell electrons, which increase by one each time a proton is added to the nucleus, until the shell is filled and it starts again, filling the next shell. Although he knew nothing about protons, Mendelev did notice gaps in his periodic table. He correctly interpreted them as four elements that were yet to be discovered. He was even able to predict many of its properties. Over time three of these elements were discovered and the gaps were filled with scandium, gallium and germanium.

But an element was still missing, right between molybdenum and ruthenium, which we assumed must correspond to a nucleus with 43 protons. For seven decades chemists searched for element 43, but it was not found in nature. It was eventually discovered, but not in the wild. In 1937, the Italian physicist Emilio Segrè obtained a molybdenum sheet that had been part of Ernest Lawrence's newly invented cyclotron particle accelerator. The sheet became radioactive in the accelerator, and Segre and his colleague Carlo Perrier were able to show that some of the molybdenum had gained a proton, transmuting it into element 43. They called the new element technetium, after the Greek word for "art." . " or "craft", so in a sense its name means "crafted element".

It is a silver-gray metal with chemical properties between manganese and ruthenium, the elements above and below it on the periodic table , just as Mendelev predicted. So why did we have to produce technetium artificially, when all the other elements can be found in nature? Well, actually technetium is produced in nature, just like other heavy elements, in the core of massive stars. Those elements eventually find their way to planets, which form from the bowels of those stars after they explode as supernovae. But technetium is so unstable that when Earth recovered from the debris. of dead stars, all the technetium had long since disappeared.

You are probably familiar with the idea that elements can be unstable. A more common term is radioactive, which we tend to associate with very heavy elements like uranium and. plutonium. For them, instability makes sense: their cores are huge, so you might expect them to have trouble holding together. But in reality any element in the periodic table can be unstable. More precisely, each element in the periodic table has unstable isotopes. "Isotope" is the word for different versions of the same element with different numbers of neutrons. For example, a carbon atom has 6 protons in the nucleus. The Carbon isotope that also has 6 neutrons is called carbon-12 because of its 12 nucleons in total, and is perfectly stable.

Now, an atom with 6 protons and 8 neutrons is still carbon, carbon-14, but it is not stable. It has a tendency for one of its excess neutrons to transform into a proton after expelling an electron and a neutrino, which transmutes it into nitrogen. The half-life of carbon-14 is about 5,700 years, although we find it in nature because it is created when cosmic rays impact nitrogen nuclei in the atmosphere. We say that carbon-14 is an unstable isotope of carbon. Each element has unstable isotopes. Some elements only have unstable isotopes, for example those with more than 83 protons, but also rare exceptions such as technetium and element 61, promethium.

And there are different shades of instability: for example, technetium-97 has a half-life of 4.2 million years, while technetium-96 has a half-life of 51 minutes. A higher atomic number tends to produce fewer stable isotopes and shorter half-lives. Elements with more than 118 protons decay so quickly that we have never been able to detect one in the laboratory. Ultimately, stability depends on the balance between protons and neutrons in the nucleus. You would think that after a century and a half of thinking about nuclear physics, we would have this all figured out by now. But in reality, the dynamics of the atomic nucleus is so complicated that sophisticated computer models are needed to understand all but the lightest elements, and many mysteries remain to be solved.

But we're getting to that point, so let's see if we can at least expose the competing influences in action. An atomic nucleus is a place of extreme forces in delicate balance. On the one hand, we have the electromagnetic force that tries to separate all those positively charged protons, and the strength of that force is great due to the proximity of the protons. On the other hand, we have the even stronger strong nuclear force that holds the nucleons together. We talked about how the strong force holds protons and neutrons together. The story of how it binds to whole nuclei is even more complicated.

It involves sending packets of virtual quarks (mesons) between nucleons. The details deserve their own episode, but the important thing is to know that this is a short-range effect. If a nucleus grows too large, the strong force cannot hold things together and various types of nuclear decay become inevitable. Although the strong force disappears quickly, its strength does not change much in the short distance where it actually acts. However, electromagnetism continues to get stronger the closer two electric charges are brought together. That means electromagnetism can overwhelm the strong force if the protons are too close together, which is another way to destabilize the nucleus.

That's why neutrons are so useful: they help separate protons so that the strong nuclear force remains stronger than electromagnetism. For smaller nuclei (up to an atomic number of 20), a uniform splitting of protons and neutrons is usually the most stable. But for heavier elements more and more neutrons are needed to provide that buffer, reaching neutron-to-proton ratios of 1.5 or more. But this is only part of the picture. It doesn't explain why the difference of a single neutron can make a huge difference in stability. It also does not explain why there is no stable isotope of technetium. To understand this we have to go beyond the common representation of the nucleus as a confusing mass of protons and neutrons.

We have to think that these nucleons have energy levels, just like electrons. You may remember the octet rule from your chemistry classes: If an electron shell has eight electrons, it is stable. This is why noble gases do not interact with anything, because their electronic shells are already complete. In this case something similar happens, there are magic numbers that complete the nuclear shells, they are 2, 8, 20, 28, 50, 82, 126 for the neutrons, and 2, 8, 20, 28, 50, 82, 114 for the protons. . The closer a core is to those numbers, the more stable it will be. All magic numbers are even, and that is because nucleons pair up according to their quantum spin, just like the electrons in their shells.

One spin up and one spin down results in zero net spin. This type of spin coupling means that even if we don't have a magic number of protons or neutrons, nuclei still prefer to have an even number of protons, or an even number of protons plus neutrons. Up-down pairs of nucleons form these stable spin-zero associations in so-called nuclear pairing interactions. Having a rogue proton or neutron with a non-cancelling spin seems to be bad for stability. Let's see if we can understand the instability of technetium using some of this. Surely we can see that 43 is not a magic number of protons, not even like its more stable neighbors, molybdenum and ruthenium.

But nearby odd-numbered elements, such as the 47-proton silver, have perfectly stable isotopes. Even giving technetium a magic number of 50 neutrons doesn't help. Neither is giving it an even total number of nucleons. Why, for example, does technetium-97 survive for 4 million years but Tc-96 decays in less than an hour? It seems there are more mysterious forces at play besides neutron filling, nuclear shell filling, and spin coupling. It turns out that there is no simple set of principles for determining nuclear stability. There are so many factors at play that the only way to solve it is to simulate the core.

And we've had remarkable success doing this using computational techniques like density functional theory, which we explained in a previous episode. These models are not yet perfect, but they make many predictions that we have verified and some that we have not. For example, the island of stability. When we combine our experimental data with our simulations we can make graphs like this. Here we can see the magic numbers. Elements with a magic number of protons have more stable isotopes and there tend to be more isotopes with a number of neutrons close to the magic neutron numbers. Patterns emerge, but not to give us clear rules about what is needed to produce a stable core.

As for unstable ones like technetium, well, they have unfortunate spots in terms of not having magic or even an even number of protons, and for whatever complex reasons there may be, there is no neutron configuration that can stabilize that unhappy nucleus. So are there elements not on the periodic table that humans can or have invented? Well, there are many. Nature can produce them, but unless that production process is ongoing on Earth, as is the case with carbon-14, short-lived unstable elements are extremely rare in nature and only appear briefly in the decay chain of other longer-lived unstable elements.

The first was technetium, but we have now synthesized 24 "artificial elements", filling in Mendelev's gaps and also extending the periodic table to 118, Oganesson, with its half-life of 0.69 milliseconds. There are elements beyond that, but we haven't made one last long enough to detect them unambiguously. But this is not the end. I have hinted at this island of stability. Our calculations show that there may be more magic numbers for a large number of protons and neutrons beyond the current periodic table. And our computer simulations agree. We're not sure what these magic numbers are, but they are apparently in the neighborhood of 184 for neutrons and 126 for protons, and could have half-lives of millions of years.

These stable elements would appear here in the graph above. A small island of stability in an ocean of hopelessly unstable isotopes, but we have not been able to reach it with the same techniques that we use to create the other artificial elements. If we want to get there, our conventional nuclear reactors and particle accelerators won't be enough, we'll have to come up with something new. But why should we even try to reach the Island of Stability? I mean, it's nice to be able to name an element, but other than that, would such a discovery have any impact on the world?

Well, probably, and possibly a big one. The eras of humanity are named after the materials we mastered at that time: the Stone Age, the Bronze Age, the Iron Age and even the current Silicon Age. And the new artificial elements have proven invaluable. For example, technetium is constantly used in medical imaging as a contrast agent, and in this case its short half-life is actually an advantage. By using an isotope with a half-life of only six hours, we can greatly reduce the amount of radiation the patient will be exposed to, while still being able to obtain useful images.

Plutonium is another example: there are no stable isotopes, but we can obtain it from uranium in nuclear reactors, where it becomes a partcriticism of the fission process in certain types of reactors. Millions of people depend on it for electricity. And then there's americium, created by bombarding that plutonium in a cyclotron to place it on the periodic table before a complex chemical extraction process. Americium is essential for smoke detectors, making it an artificial element that has saved many lives. The elements that we will discover on the island of stability will be very heavy, initially difficult to synthesize and somewhat radioactive.

But some are sure to have unexpected and perhaps powerful applications. We discover hints of these islands of possibilities beyond the limits of the known. What can we do but hold our breath and leap towards them, hoping to gain new ground in humanity's journey into the further, future horizons of space-time? As always, thank you very much to everyone who supports us on Patreon. Seriously, we wouldn't be here without you. Special thanks today to Glenn Sugden, who supports us at the quasar level. Glenn, as a thank you for your generous support, we will name element 267 after you. The suggestion is great.

It is slightly radioactive, extremely useful in medical imaging, and is the fundamental catalyst for low-temperature fusion. A beautiful violet tone shines on top. Glenn, thank you for your support. We will send you a gram of sugdenium as soon as it is invented. In our last episode we talked about grabby aliens. That is the hypothesis that the future emergence of new civilizations has to be interrupted at some point, or else humanity will arrive surprisingly early in the universe. And the limit is when the universe is completely colonized by... yes, grabby aliens. Elijah Zayin makes a thoughtful critique of using the Copernican principle to argue that we can't do it especially in the early stages of the universe.

To paraphrase: even if there is very little chance of a given civilization being one of the first, someone has to be the first. So there will always be a civilization that ends up "confused" about why it is so early. Here we come to the most controversial aspect of anthropic reasoning. If I maintain that I should be in the most typical circumstances consistent with my existence, what circumstances does that exclude? Nick Bostrum's auto-sampling assumption attempts to clarify this. He says that other things being equal, an observer must reason as if he were randomly selected from the set of all actually existing observers (past, present, and future) in his reference class.

So the trick is to find out what its reference class is. For example, if I define my reference class as a biological being, then I should not be surprised if I am not in an uninhabitable place. But that allows for the 4 billion years of habitability prior to my birth. Why am I in the least brutal of those 4 billion years? Just luck? But if I define my reference class as those who are capable of formulating anthropic arguments, then it is less surprising that I live in a modern civilization. But then why can't I define my reference class as “those who observe an empty universe”?

After all, I am my mental experience, and the mental experience of seeing an empty universe is what made me ask these questions in the first place. Being a member of a primitive species is one of the few circumstances consistent with who I am. You could say that this is an overly restrictive way of defining your reference class, but the fact is that there is no clearly correct way to do it. This whole anthropic thing is pretty confusing. Tristan Cleveland points out that life may have had the potential to arise many times in the beginning, except for the fact that once one incident of life began and progressed, it would be very difficult for it to happen a second time.

That second incidence would surely be devoured by the first incidence, now more evolved. In fact, we see that the DNA of all life clearly comes from a single common ancestor. So if this dynamic occurred on Earth, it makes sense that it could happen throughout the universe. And that is exactly what the study we analyzed suggests. That over time the emergence of new civilizations will be prevented. They may not be eaten, but they cannot emerge naturally in a fully colonized universe. Several of you liked the idea that later civilizations could consider us ancient. For example, doctors like to someday refer to us as "the old ones," with our ancient technology and ruins scattered throughout the universe.

Let's make sure we're the omniscient, benevolent kind of "old guys." instead of the Lovecraftian tentacle type. Because you know that's another solution to the Fermi paradox: that the first civilization turned into cosmic horrors, destroying everything that came after, just as life probably did on Earth. we want to arrive early... better than them. Or do we just hide? Of course, it is exactly this thought that gives you the dark forest solution to the Fermi Paradox.