Getting back to new elements:
The number of the protons in an atom's nucleus is what defines an "element". The number of neutrons in an atom's nucleus may be different for the same number of protons, so the various numbers of neutrons make the atoms different "isotopes" of the same element. For instance, hydrogen atoms most usually have just a single proton in the nucleus, but can also have one or two neutrons accompany the proton. These heavier isotopes of hydrogen are given specific names (deuterium and tritium), but most isotopes are simply called by their element name and the total number of protons plus neutrons. For example, carbon has six protons and six, seven or eight neutrons, and those isotopes of carbon are simply called "carbon-12", "carbon-13" and "carbon-14". The first 2 are stable, while carbon-14 is radioactive and decays with a half-life of 5,730 years. Carbon 14 would decay away to undetectable levels if it was not constantly being produce in our atmosphere by cosmic rays (by a process that I won't go into for this post).
For the most part, all isotopes of a particular element have about the same chemistry, because the number of electrons in an (electrically neutral) atom is the same as the number of protons in its nucleus, and the energy levels of those electrons is also mainly a function of the number of protons. So, for instance, the chemistry of carbon-14 in our bodies is the same as that of carbon-12. Scientists use the fact that just about everything alive absorbs some carbon-14, while alive, but after death, it decays away with that half-life of 5,730 years. So, they can measure the amount of remaining carbon-14 to estimate how long something has been dead, at least for periods on the order of tens of thousands of years.
Anyway, there are a lot of processes that change atoms from one element to another, including fission (splitting of a nucleus into smaller pieces), fusion (combining 2 or more nuclei into one heavier nucleus), radioactive decay (the nucleus spitting out electrons - known as beta particles, protons, neutrons or helium nuclei, known as alpha particles), or spalling where something like a neutron hits a nucleus and a proton comes out - which is how carbon-14 is made from nitrogen-14 atoms.
We think that atoms of elements heavier than helium (element #2) have all been produced by fusion in stars long after the "Big Bang" produced the original hydrogen and helium. Some of that production was due to gravity-induced extreme pressure and extreme temperatures in the center of stars fusing nuclei together. That got elements up to iron (element #26 with a bit more than that number of neutrons), but beyond that, it takes more energy to fuse elements with even more protons than the energy that is released by their fusion process. So, at some point, stars run out of fusion fuel and gravity makes them collapse. That collapse suddenly makes tremendously high pressures and is thought to very quickly make the heavier elements,
at least up to uranium (element #92) before the star explodes as a supernova. But elements with more than 82 protons (lead) are all unstable and experience radioactive decay, so they do not last forever, and only a few like uranium-235 and uranium-238 have lasted the billions of years that it took for our solar system to form from the dust of long-ago supernovas. Most of the elements on Earth that are heavier than lead are the products of the radioactive decay chains that start with Uranium and Thorium and end at stable isotopes of lead.
So, depending on how long ago a star went supernova and made a lot of heavy elements beyond lead, less of those heavier-than-lead elements will be around as those remnants age. We do know that element 92 gets made by star supernovas. But we don't know how many other, maybe heavier elements also get made and have already decayed away before humans evolved and started looking for them.
We do know that humans can make uranium atoms fission and release neutrons that get absorbed in other heavy element nuclei and make elements heavier than uranium. For instance, Uranium-238 can absorb a neutron and emit a beta particle and become plutonium-239, which is also radioactive and decays faster than uranium-238. We call plutonium "man-made" but it was also probably made in star supernovas, too, and has just decayed away by now, around this part of our galaxy.
We also know that humans can make heavier atoms by shooting nuclei of one type of atom at another type of atom with enough energy to make then fuse into a new element. That is how we got up to element #118. But, those elements decay very fast, and are of little value for anything beyond experiments used to develop the theory of how atomic nuclei work in nature.
The theory of the atomic nucleus structure is not completely developed, even now, so there is some conjecture that, well above element #118, there might be some stable isotopes, or maybe some that just live long enough to have some usefulness - which I think was your question. I will let you read about that here:
https://en.wikipedia.org/wiki/Island_of_stability .
The question is, if there really are elements that are stable or at least long-lived in a radioactive sense, why are we not finding them in nature? Do they not get produced in supernovas? It seems likely that all sorts of elements with more protons than 92 get produced in supernovas and just have such short half-lives that they have all decayed away by now. And, trying to look closely at the remnants of recent supernovas to find elements that we do not already know about is tricky, because we don't have any good way to know what to look for. There are some theories about what those elements would look like in emission spectra, but who knows if those theories are correct?
So, the odds seem low that we will find any new elements with long enough lifetimes to be useful. And, if we do find some, there is no reason to assume that they will have some magical properties. They will certainly be very heavy.
The thing that is most likely to show us some unexpected and perhaps very useful new physics is this question of what is "dark matter". We know so little about it that we have no idea if it could give us a way to do things we now think are not possible. But, that is the type of hope that keeps scientists probing for more understanding.
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