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We've synthesized all elements up through oganesson, element 118. It's interesting that this heaviest element completes row 7 of the periodic table (I've heard it's theorized to have quite different chemical properties from the noble gasses, but that's beside the point). Since nuclear orbitals are fairly different from electron orbitals, there's no reason this has to be the case.

I know many attempts have been made to synthesize elements above oganesson. From what I understand, these heaviest elements were often made by hitting lighter transuranic elements with calcium-48, because calcium-48 has a high neutron-to-proton ratio. The result (if successful) is a nucleus with 20 more protons. Since einsteinium and fermium have notably shorter half-lives than berkelium and californium, it's hard to make elements heavier than oganesson this way. But if this is the main reason, I don't see any connection to rows of the periodic table.

So, is there a reason that the heaviest element we've synthesized happens to be in the noble gas column, or is it a coincidence?

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    $\begingroup$ To quote the alt text here: "It's nice how the end of the periodic table is flush with the edge these days, so I think we should agree no one should find any new elements after #118 unless they discover a whole row at once." $\endgroup$ Commented yesterday
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    $\begingroup$ Ah! How did I miss that xkcd? @J.G. Thanks! $\endgroup$ Commented yesterday
  • $\begingroup$ Starting with uranium, about 20 different elements have at one point been the heaviest known element. I'm not sure if the fact that one of those 20 is in the noble gas group even rises to the level of being a coincidence. $\endgroup$ Commented 6 hours ago

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It's a total coincidence.

Also I don't think there's evidence that the electron configuration for oganesson actually corresponds to a noble gas. (The NIST database, updated late 2024, stops at hassium, which is in the iron group.) A closed valence shell like those of radon, xenon, and friends is certainly a very probable configuration for oganesson, but things have an annoying habit of behaving differently in unexplored territory.

The chemistry of heavy elements in general is different from the chemistries of their lighter cousins. A major factor is that, for the innermost electron orbitals, relativity is non-negligible. It's easy to find arguments that relativistic corrections are responsible for the color differences and reactivity differences between gold and its cousin silver, or between liquid mercury and its solid cousin cadmium.

I personally have a hard time taking claims about the chemistries of superheavy elements seriously, because in general it's impossible to collect a large enough sample for them to exhibit any collective behavior. For example, twenty years ago, it wasn't obvious whether copernicum ($Z=112$) would act more like its cousin mercury or more like radon. The radon argument was (I think) based on group 12's position at the end of the $d$-block of the periodic table, and some idea that relativistic effects might make the full $d$-shell more important than the empty $p$-shell. The radon-like low-reactivity argument was supported by a 2001 paper which reported zero copernicum detections out of "about three" expected. But the mercury-like high-volatility-metal argument was supported by a a 2007 paper which detected two copernicum atoms; part of their argument depended on whether the implantations were shallow versus deep in the detector.

The press at the time reported "element 112 is a liquid!", which is just not a statement I feel is supported by two atoms' worth of data. I haven't followed the literature since, but the 2007 paper is still today the citation on Wikipedia at the sentence "copernicum may be a gas or a volatile liquid at STP."

As another answer points out, $Z=118$ is not close to a nucleon magic number. The proton magic numbers at $Z=20,28,50,82$ are well-attested by the fact that calcium, nickel, tin, and lead each have approximately a zillion stable isotopes. Neglecting relativistic effects we'd predict the proton and neutron magic numbers to be the same, which is also attested by nuclear stability and abundance data. There is a huge change in nuclear stability above the $N=126$ magic number, obvious on any table of isotopes; this suggests the next proton closed shell should be near $Z\approx 126$ as well.

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    $\begingroup$ Note that nuclear pairing effects make it likely that even-$Z$ nuclei may be produced before their odd-$Z$ neighbors. I happened to have a 2016 period table on my shelf, in which the name flerovium (114, first observed 1999) is official, while nihonium (113, first observed 2003) still has only a provisional name. I'm sure I could dig one up that has it labeled as Uut (ununtritium, or one-one-three-ium in pseudolatin), and I very vaguely remember a 2001-era table with Uuq hanging off the bottom like a loose tooth. $\endgroup$ Commented yesterday
  • $\begingroup$ Typo: Where you wrote $Z=118$, clearly should be proton magic number rather than neutron. The next part where you used "neutron magic number" is not clear if you meant proton or neutron; my Wikipedia link included a direct assertion that the next neutron magic number will differ from the next proton magic number; in either case, the neutron magic number is irrelevant to the element number, which is why I chose not to emphasise that in my answer, but to each their own. It is an interesting thing to discuss. $\endgroup$ Commented yesterday
  • $\begingroup$ Not a typo (it says "nucleon"). But you are right that it was a little too terse. Thanks for the feedback. $\endgroup$ Commented 22 hours ago
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I elect to preserve an upvoted comment by another user:

10 years ago this was not the case. So, coincidence…

On top of the upvoted comment above (+1), it is also highly suspected that Oganesson's proton number is not a magic number, with a magic number coming up soon after that (and also before, but we already have those detected). As such, it is highly unlikely that this "coincidence" will even stay as-is. At least it makes more sense to expect that a doubly-magic nuclei would be where we will decide to stop wasting incredible efforts (and monstrous amounts of money) to find more.

Watch the YouTube video. It is very very very entertaining and informational.

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Purely coincidental.

The title of this paper: "Oganesson: A Noble Gas Element That Is Neither Noble Nor a Gas" summarizes it best.

Only five atoms of $\text{Og}$ have been produced with an estimated mean lifetime of $0.7$ ms. With such scarcity of material and too short a lifetime for producing meaningful chemical reaction experiments, not much can be said for sure about this particular element. Hence most of its properties are estimated from a relativistic quantum theory or other computational approaches. These predict that Oganesson melts at a $\approx52 ^\circ$ C temperature and that this element actually is a semiconductor. So, we can call $\text{Og}$ a "noble gas solid", which would describe it best and amplify its differences from other noble gasses.

By the way, the next $\text{Group}~18$ element "to be found" would also likely have melting properties similar to Oganesson, since if we chart noble gasses melting temperatures, they only increase with atomic number.

enter image description here

So it seems that there's no more gasses in a noble gas group after $86$ element.

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  • $\begingroup$ That melting point trend seems pretty close to linear, aside for Oganesson. Is that coincidence, or is there something about Oganesson which makes it buck a trend? (e.g. like relativistic effects changing Au/Hg properties.) $\endgroup$ Commented 10 hours ago
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    $\begingroup$ As an article states, relativistic effects shifts melting temperature up by about $100K$, but we should not forget that for $\text{Og}$ this is just an estimation (modelling) of a melting property, while for the other noble gases- these melting points are more or less confirmed experimentally (measured). So we can't actually align linear trend to Oganesson simply due to the fact that we be comparing apples to the oranges. $\endgroup$ Commented 7 hours ago
  • $\begingroup$ This made me wonder whether anyone has ever produced a sample of liquid radon. Apparently just once, in 1909. $\endgroup$ Commented 31 mins ago

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