TIL about the end of the periodic table
Jun. 18th, 2011 08:50 pm![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
sniffnoyI guess this is must be well-known among anyone who knows nuclear stuff but it was new to me. I was looking up some stuff about super-heavy elements the other day and I was surprised to learn that the periodic table is not infinite, with atoms just getting less and less stable (with occasional islands of stability) as you go on, but rather that it's thought that past Z=173 atoms are thought to be impossible. I'm not entirely too clear on what that means - my first reaction is "Well you could still drive the particles together even if they decayed quickly, unless you want to say it would decay 'instantaneously' or something like that". Wikipedia makes it clear it's only talking about neutral atoms, the problem is that atoms that large couldn't hold their electrons. I guess then it means that atoms that large would lose their electrons before their nuclei decayed? Though that seems to me to not really an "end" to the periodic table, if they could exist in salts. But I guess past that point chemistry as we know it must pretty much break down entirely, so I guess that's an end.
Actually more naive models have the periodic table ending at Z=137, where here 137 comes from 137=⌊1/α⌋ (α being the fine-structure constant). But accounting for relativistic effects pushes things up to 173 (or so it's thought?). But then apparently these are just upper bounds and the end could be lower than that! Though I'm not sure how you'd tell that a given atom was impossible.
But what really surprised me is that the periodic table as we know it may break down in periods 8 and 9 (and maybe a bit even at the end of period 7) before the atoms end entirely! Due to relativistic effects. I'd heard that relativistic effects were important with large atoms, being responsible for e.g. the color of gold, but I had no idea they could cause things like this. Pekka Pyykö modeled the atoms up to Z=172 by computer and found that due to relativistic effects, their electron shells wouldn't even fill in the usual order! Take a look at the periodic table he's drawn up for them - grouped by predicted properties, by electron shells, no longer in order of increasing atomic number. And even in period 7 it's thought that element 114 will probably act more like a noble gas than element 118! (I was also surprised to find that Copernicium is actually stable enough that people have been able to definitively pin down that yes, it really is a transition metal and really does act like a heavier analogue of mercury. Only element with Z≥109 anyone has managed to do this for, it would seem.) And of course due to the end of the periodic table, there's no such thing as an h-block element. (Though I guess his simulations suggest that indeed the periodic table doesn't end before 172? Must wonder why he didn't do 173... actually looking at the original paper I notice he says others have put the limit at 175? And that actually it should be higher and that the models generating these numbers are still a bit simplistic? Oh boy...)
So super-heavy elements are a hell of a lot weirder than I would have guessed. There's no way that quantum gravity effects could become relevant for these, right? :-/
(Also, I need to go bug Steve about CDN shit again. Goddammit.)
-Harry
Actually more naive models have the periodic table ending at Z=137, where here 137 comes from 137=⌊1/α⌋ (α being the fine-structure constant). But accounting for relativistic effects pushes things up to 173 (or so it's thought?). But then apparently these are just upper bounds and the end could be lower than that! Though I'm not sure how you'd tell that a given atom was impossible.
But what really surprised me is that the periodic table as we know it may break down in periods 8 and 9 (and maybe a bit even at the end of period 7) before the atoms end entirely! Due to relativistic effects. I'd heard that relativistic effects were important with large atoms, being responsible for e.g. the color of gold, but I had no idea they could cause things like this. Pekka Pyykö modeled the atoms up to Z=172 by computer and found that due to relativistic effects, their electron shells wouldn't even fill in the usual order! Take a look at the periodic table he's drawn up for them - grouped by predicted properties, by electron shells, no longer in order of increasing atomic number. And even in period 7 it's thought that element 114 will probably act more like a noble gas than element 118! (I was also surprised to find that Copernicium is actually stable enough that people have been able to definitively pin down that yes, it really is a transition metal and really does act like a heavier analogue of mercury. Only element with Z≥109 anyone has managed to do this for, it would seem.) And of course due to the end of the periodic table, there's no such thing as an h-block element. (Though I guess his simulations suggest that indeed the periodic table doesn't end before 172? Must wonder why he didn't do 173... actually looking at the original paper I notice he says others have put the limit at 175? And that actually it should be higher and that the models generating these numbers are still a bit simplistic? Oh boy...)
So super-heavy elements are a hell of a lot weirder than I would have guessed. There's no way that quantum gravity effects could become relevant for these, right? :-/
(Also, I need to go bug Steve about CDN shit again. Goddammit.)
-Harry
