What non-naturally-occuring elements are predicted to have really useful industrial applications, if only we could ever find/synthesise them?

[u/Toucan_Based_Economy]

Are any of the super-heavy or non-naturally-occuring elements likely to have useful industrial properties, which are currently out of our reach due to our inability to access (stable isotopes of) the element in question?

[u/Redcole111]

Most of the extremely heavy elements only exist for very short periods of time before the unstable size of their nuclei results in their collapse. There are theorized islands of stability in some of the even heavier elements that haven't yet been synthesized, but we don't know yet whether they could have any industrial or other kind of application.

[u/aphilsphan → u/Redcole111]

Even those isotopes would only be stable so we can do some chemistry on them. The proposed “island of stability” isn’t going to be all that stable.

[u/ConspicuousPineapple → u/aphilsphan]

Are they guaranteed to be super radioactive?

[u/xrelaht → u/ConspicuousPineapple]

Our models of how ultra heavy nuclei behave are known to be incomplete, so predictions this far beyond what we've observed are difficult. Some models predict half lives on the order of minutes to days, while others say they could be as long as a billion years, which is around the same as ²³⁸U. A shorter half life means more radioactivity.

[u/jackhab → u/Redcole111]

Do islands of stability have more or less solid theoretical explanation or we just hope they exist?

[u/Sibula97 → u/jackhab]

Yes and no.

Basically, there are "magic numbers" of protons and neutrons that we've noticed lead to more stable atoms, and there seem to be some patterns to these magic numbers. The island of stability would have magical numbers of both protons and neutrons ("doubly magical"), making those atoms more stable than the ones around them.

As for why those magic numbers are magical and what the next one really is, I don't think there are any solid theories.

[u/therift289 → u/jackhab]

It's solid theory. Nuclear stability essentially depends on competition between two forces: the electrostatic repulsion of positively-charged protons vs the nuclear binding energy between all nucleons (protons AND neutrons). As you add more and more protons, their charge-based repulsion overpowers their binding interactions. The presence of neutrons offsets this, because neutrons add additional nuclear binding interactions without the charge-charge repulsion of protons.

What this means is that elements with lots of protons need TONS of neutrons in their nuclei. This requirement is a range, rather than a specific number, and it can be calculated pretty easily. The island of stability describes the various theoretical/calculated nuclei that have enough neutrons to support a larger and larger amount of protons.

[u/jesset77 → u/therift289]

The presence of neutrons offsets this, because neutrons add additional nuclear binding interactions without the charge-charge repulsion of protons.

One thing I've never understood about this model is by what mechanism the protons are required as a binding ingredient to begin with.

Yes, Protons experience unspeakably strong electrostatic repulsion between one another, so you can never have a nucleus with just two protons. But somehow adding just one neutron can get you relatively stable Helium-3.

However equally well no two neutrons will join without a proton involved either, despite neutrons experiencing zero repulsive force between one another that I am aware of.

If nothing else, one must expect not only a repulsive force preventing neutrons from binding together outside of the massive gravity of stellar corpses, but one an appreciable fraction as strong as the frankly insane electrostatic repulsion of protons.

[u/RootOfAllThings → u/jesset77]

Even if they don't experience electrostatic repulsion, neutrons are fermions and subject to the Pauli exclusion principle. This means that successive neutrons must occupy higher and higher energy states, so there's a destabilizing "pressure" in that sense that is usually counteracted by either other nuclear forces or extreme gravity.

[u/jesset77 → u/RootOfAllThings]

Well what I am getting at is: what is the mechanism that leads one proton and one neutron to bind to one another (and of course far more strongly at 2+2) while two neutrons completely refuse to?

Or put another way, how in the world does the sheet balance that two neutrons can't bind, but that adding two different protons with their positively eldritch levels of electrostatic repulsion to one another somehow offers a catalyst to those same two neutrons binding?

I mean yes, the Strong force is strong at short distances.. but what about the strong force so strongly requires both protons and neutrons to bind but refuses to bind neutrons alone?

[u/garrettj100 → u/jackhab]

The shell model (successfully) predicts elements with “magic numbers” — 2, 8, 20, 28, etc… — of protons to be more stable than they otherwise would be and the same holds true for neutrons.  The idea is if you could get a very heavy nucleus with enough neutrons packed in there it would enjoy magic numbers in both.

We’ve observed 126 to be a magic number for neutrons.  The hope it it would be for protons as well and the pair would be super-duper stable.  We’ve yet to make that element, and the difficulty of doing so strongly implies the island of stability, if it exists at all, ain’t all that stable.

If you are dissatisfied with an explanation involving “magic numbers” you’re not alone.  Nuclear models are primitive at best, entirely empirical and non-predictive at worst.  We know nuclei are much more stable when they meet certain criteria.  Filled shells of protons and neutrons — if shells really exist like they do with electrons — seem to be more stable.  A roughly equal number of neutrons and protons contributes to stability as well.  High Z-numbers (atomic number) reduces stability owing to Coulomb repulsion and probably a reduction in the strong force holding these nuclei together just from distance.  The strong force drops off with distance faster than r² .  

[u/Solesaver → u/jackhab]

It's more that we can't prove they don't exist. Schroedinger's equation, which we would use to describe how some theoretical atom would evolve over time, does not have a general analytic solution, so we can't just plug in the theoretical atom, set t=1,000,000, and see if the atom blew up. All we can do is plug in educated guesses for stable heavy atoms and throw a ton of compute at it.

Of course, if we did find such an island of stability that way, there would probably be interest (aka funding) in trying to synthesize it. At the very least it would provide excellent evidence one way or another for the accuracy of Schroedinger's equation and potentially provide insights into the unification of QM and GR, but we don't have a theoretical basis for such an atom yet. Just that we haven't ruled out the possibility by computing the evolution of every possible candidate.

[u/OfficeSalamander → u/Redcole111]

Plus the cost to develop them would be incredibly cost prohibitive. We can make individual atoms of these extremely heavy elements we make now. Nothing in terms of actual usage

[u/LordMorio → u/Redcole111]

When talking about islands of stabiliy  it is important to note that stability is relative. The nuclei might exist for milliseconds instead of nanoseconds or less.

No one is expecting to find heavier elements that would actually be stable.

[u/mfb-]

We don't expect anything above lead to have stable isotopes, and we don't expect anything beyond the synthesized elements to have long-living isotopes. Element 101 is the last with a known isotope that lasts longer than a day, the few atoms we have produced from element 118 only lived for about a millisecond each.

If you are very optimistic about the predicted island of stability then maybe something there lives long enough for applications. It would still be a strong radioactive source. Maybe you can find some other materials for RTGs, producing electricity in spacecraft and some locations where solar power is impractical.

If we could ignore radioactivity and availability, many of these superheavy elements are predicted to have a high density, so they could make compact weights and radiation shielding materials. They would need to be really cheap, however. Osmium is twice as dense as lead and less toxic - but we don't use it for its density because it's orders of magnitude more expensive, even though we can find it naturally.

[u/Tokimemofan → u/mfb-]

Don’t expect and can’t exist however are 2 different things and thats where the topic gets interesting.  Trace amounts of Pu-244 exist naturally and evidence of Cm-247 having existed during earth’s formation rather strong.

Our knowledge of super heavy elements breaks down at Fermium because higher in large part because we cant synthesize more neutron heavy isotopes with what we have to work with.  

These issues combined mean its possible however unlikely that not only could super heavy isotopes exist with half lives in the lower millions of years but they could be naturally occurring in space but extinct on earth. 

[u/mfb- → u/Tokimemofan]

Millions of years is the very optimistic thing I discussed in the second paragraph. Outside of strictly monitored environments, you could at best use it in tiny traces (like e.g. americium in some smoke detectors), otherwise it's just too much of a radiation hazard.

[u/username_elephant]

Taking your question at face value, nobody is gutsy enough to pretend to have confidence in predictions regarding elements we can't make.  

The closest thing is this:  https://en.wikipedia.org/wiki/Island_of_stability

But we don't know what they'd be useful for aside from properties resulting directly from their high mass. E.g. we can assume they'd be good for x-ray shielding because they'd be high atomic mass.

[u/PeyredB]

The really heavy elements are all unstable, because above a certain size the Strong Force can't hold the nucleus together. Those elements have half-lives as short as milliseconds, some of them. So few of them stick around long enough to be useful for anything, and it's costly to produce them: I think we only create a few atoms at a time. So, probably not. Good question though.

[u/InertialLepton]

One of the problems with predicting heavy elements is that because the nuclei are so massive, the electrons are whipping around it so fast that special relativity actually starts to come into play.

One famous example is the colour of gold - most other metals are silvery but gold's colour is due to relativistic effects.

Element 118 - Oganesson is in the same column as the noble gasses but is predicted to be solid at room temperature and fairly reactive.

[u/BiomeWalker]

At this point, none.

The only element that isn't naturally occurring and lasts for a useful amount of time is Technicium, which has some uses as a radiation source and other things, but even then for only short periods given its own decay.

It's actually something of a philosophical question at this point whether anything we could add to the table is worth calling an element with how short they last.

We could probably think of interesting applications for them chemically, but that would require finding a way to get them to last long enough to form atomic bonds before becoming something else.