The Search for the Final Element
Identifying Every Different Kind of Atom that Could Theoretically Exist in the Local Universe
Early in the 19th century, a pioneering chemist named Johann Wolfgang Dobereiner noticed that certain chemical properties repeat when the elements are placed in order of increasing mass. That is to say, halogens, alkaline metals, and alkaline earths always occurred in the same order. Then, once Dobereiner’s pattern was established, another trailblazing chemist, named Dmitri Mendeleev, tabulated the sixty-one elements that were known at the time. This helped set the stage for modern-day chemistry.
It did this by allowing Mendeleev to see blank spaces where other elements should exist. This gave him the ability to predict undiscovered atoms on the old vertical row model, setting him apart from everyone else in his field. As if that wasn’t impressive enough on its own, in 1871, Mendeleev rearranged the elements, putting the ones with similar chemical properties in the same vertical columns. That one simple act totally revolutionized chemistry from that moment on, because the resulting chart became the classic periodic table of elements.
The question is if hydrogen is the first element on the list, then what will the last element be? What’s the heaviest possible superheavy element that could ever exist? Put another way, if hydrogen (element 1) is made up of the smallest atoms with the least amount of protons and electrons, then what element is, or could be, made up of the largest atoms with the most protons and electrons? Is there a biggest element, whose atoms are so big that there couldn't possibly be anything bigger? Logically, there must be. So, it’s not just theoretically possible that there’s a limit. There is definitely a finite amount of matter that can go into an atom, thereby restricting how massive one can become.
A major problem in all of this is that as the nuclear charge goes up, the velocity of the innermost orbiting electrons also increases, and this causes strange things to happen. Normally, as you add more protons to a nucleus, the mass of an atom increases making it denser, forming a more robust object. However, for very massive atoms, the force holding them together becomes unstable and they tend to break apart through radioactive decay. Thus, very massive atoms such as nobelium (element 102) and lawrencium (element 103) have lifetimes that are very short. Specifically, the longest-lived isotope of lawrencium is 266 with a half-life of 11 hours.
The issue is that this gets out of hand very quickly. The half-lives of superheavy elements diminish very rapidly. This makes understanding them very difficult. For flerovium (element 114) it’s 2.6 seconds, for livermorium (element 116) it’s 0.06, and for oganesson (element 118) it’s 0.002. In sharp contrast to this, the heaviest element found in any appreciable amount on Earth is uranium (element 92). More to the point, the half-life of uranium-238 is about 4 billion years, uranium-235 about 700 million years, and uranium-234 about 25 thousand years.
Above and beyond the level of uranium, scientists are able to create new elements in atom smashers, otherwise known as particle accelerators. This is done by colliding a beam of lighter atoms into a target of heavier atoms. As an example of what I mean, labs have smashed calcium (element 20) into curium (element 96) to make livermorium (element 116). The thing is that the world-renowned physicist Richard Feynman argued that the last possible element would be feynmanium (element 137) because after that the electrons of 1s orbital would have to travel faster than the speed of light, which is theoretically impossible.
Unfortunately for Richard Feynman, as it turned out, he was right about the effect but wrong about the element, so when the proper calculations were done by Pekka Pyykko, he came up with element 173, not 137, as the highest possible atomic number that could ever exist in this space-time continuum. The math proves that beginning with unseptrium (element 173), the probability of making two nuclei come together gets smaller and smaller as experimenters go up higher and higher in atomic numbers. This makes the existence of any atoms above element 172 highly unlikely.
Regardless, because resistance to fission drops as the charge in the nucleus goes up, the elements that are being made have shorter and shorter rates of stability, meaning they decay faster and faster. Plus, as more and more protons are added on, it takes longer and longer to make superheavy elements. To put everything in perspective, with rutherfordium (element 104) scientists can make several atoms per minute, with seaborgium (element 106) they can only make several atoms per hour, and with hassium (element 108) they can only make several atoms per day, and so on and so forth.
Meanwhile, no predictions for half-life or decay modes are currently available for elements with an atomic number greater than 175. However, well beyond that, unoctquadium is a hypothetical chemical element that has an atomic number of 184. It’s known by the temporary symbol Uoq. In regards to this, the nuclear charge of element 184 is believed to be so great that stationary-state orbital theory can’t describe its electrons. So, it’s highly implausible that neutron capture can form any Uoq isotope whatsoever, meaning it would be impossible to synthesize the element altogether.
Regardless, in the not-too-distant future, superheavy elements will inevitably force chemists to reinvent the periodic table of elements, in a new crowning achievement in human thought. In regards to that, it’s possible that they might even expand from the 18 column version to the more accurate 32 column version, and then continue on from there. Although I seriously doubt it. Either way, the issue is that humanity needs more powerful machines to produce heavier and heavier elements, like element 121, if it exists. Until then every element that has not been synthesized will remain purely hypothetical, so the image below is what the ultra-long periodic table of elements should look like up to this point.
Beyond this, element 119 could be really special because it will begin the eighth period, which would add an eighth row to the table. That is unless the left-step table designed by Charles Janet is a more accurate model, which I suspect it is, as shown below (note the added layer of periodicity, as revealed in the pattern on the right). When read from top to bottom and left to right, it gives the exact order in which electrons fill up an atom’s available energy shells. Therefore, if the left-step table is employed then it’s more likely that element 121 will begin the eighth period, which is what I believe. Either way, even just making elements 119 and 120 to fill in the left-step table will be very difficult.
The problem is that scientists have currently run out of suitable target materials with which to make the next generation of superheavy atoms. That is to say, to make element 119 chemists need to have enough of element 99 on hand. The problem is that einsteinium is a very difficult element to make. So, there are ideas of using either titanium (element 51) or chromium (element 54) with the existing targets. The problem is that with these elements the chances of a successful collision taking place are much less than with calcium, so you need a much more intense beam, which costs a lot more money.
With that being said, as of the time of this writing, element 118 is currently the final element. However, that doesn’t mean that other superheavy elements are necessarily science fiction. It only means that physicists and chemists haven’t been able to produce them yet. With that in mind, the only reason that we shouldn’t put every element from 119 to 172 on the periodic table is that we don’t know for sure that they can all really exist. In that sense, the final element is merely the most recent superheavy element that scientists have been able to synthesize, and it always will be. So, in spite of all the speculations and calculations that have been done, only time will tell when and where the last cutoff will actually occur. Then, and only then, the periodic table of elements will finally be complete.