The Student Room Group

Why no gaps in the periodic table?

There aren't any gaps in the periodic table i.e. elements yet to be discovered that have less protons than ununoctium- but how do we know that?

Elements are distinguished by their numbers of protons so I guess what I'm asking is, essentially, whether it would be possible to have 'fractional' protons if that makes sense.

I know protons are each composed of three quarks and could possibly decay but I don't know much particle physics beyond that. Not sure if this is a dumb question but thank you for your help!
Reply 1
Original post by fizzers
There aren't any gaps in the periodic table i.e. elements yet to be discovered that have less protons than ununoctium- but how do we know that?

Elements are distinguished by their numbers of protons so I guess what I'm asking is, essentially, whether it would be possible to have 'fractional' protons if that makes sense.

I know protons are each composed of three quarks and could possibly decay but I don't know much particle physics beyond that. Not sure if this is a dumb question but thank you for your help!


Basically no. Quarks must be bound together in either a meson or baryon (ignoring quark-gluon plasma).

Give this a read.
Reply 2
Original post by alow
Basically no. Quarks must be bound together in either a meson or baryon (ignoring quark-gluon plasma).

Give this a read.


Thank you very much! Why is that so?
Also, I know that protons wouldn't be protons anymore if they didn't have two up quarks and one down quark, but could there be elements with other combinations of quarks that can substitute protons?
Original post by fizzers
Thank you very much! Why is that so?
Also, I know that protons wouldn't be protons anymore if they didn't have two up quarks and one down quark, but could there be elements with other combinations of quarks that can substitute protons?


Elements are defined by the number of protons in the atoms nucleus. Isotopes of any given element have a different number of neutrons in the nucleus.

Neutrons have two down and one up quark. Neutrons convert to protons during beta-decay (producing a new element) and at the same time o producing an electron and anti-neutrino.

Protons convert to neutrons by the absorption of a W- boson.

These tables summarise the different combinations:

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/baryon.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/meson.html#c1
(edited 9 years ago)
Reply 4
Original post by fizzers
Thank you very much! Why is that so?
Also, I know that protons wouldn't be protons anymore if they didn't have two up quarks and one down quark, but could there be elements with other combinations of quarks that can substitute protons?


All baryons (the ones with 3 quarks like protons) are unstable with the sole exception of protons. Neutrons when bound in nuclei are also stable, but I don't think anything else is even when in nuclei. Other quark combinations would simply decay.

You can't get less than one proton because of a process called colour confinement which I don't even vaguely understand in it's gory detail, but the pop science explanation is that as you separate colour charges (i.e. unbound quarks) the strong force increases rather than decreases and you eventually get enough energy stored to make new quarks via E=mc2. This stops lone quarks existing. Mesons and baryons (quark-antiquark and triple quark respectively) are AFAIK the only stable combinations. Certainly they're the only ones we've found, but I don't know if you can theoretically get 6 quark combinations.

Lastly, the 'protons are up, up, down' line is a tiny bit wrong. It's more like they're a massive mess of quarks that happens to work out at being uud when you work out what cancels what. I.e. protons are only net uud.

That's pretty much everything I know on this. I can try to explain anything more clearly if you wish.
Reply 5
Original post by lerjj
All baryons (the ones with 3 quarks like protons) are unstable with the sole exception of protons. Neutrons when bound in nuclei are also stable, but I don't think anything else is even when in nuclei. Other quark combinations would simply decay.

You can't get less than one proton because of a process called colour confinement which I don't even vaguely understand in it's gory detail, but the pop science explanation is that as you separate colour charges (i.e. unbound quarks) the strong force increases rather than decreases and you eventually get enough energy stored to make new quarks via E=mc2. This stops lone quarks existing. Mesons and baryons (quark-antiquark and triple quark respectively) are AFAIK the only stable combinations. Certainly they're the only ones we've found, but I don't know if you can theoretically get 6 quark combinations.

Lastly, the 'protons are up, up, down' line is a tiny bit wrong. It's more like they're a massive mess of quarks that happens to work out at being uud when you work out what cancels what. I.e. protons are only net uud.

That's pretty much everything I know on this. I can try to explain anything more clearly if you wish.


Thank you for the detailed answer especially for pointing out the 'uud' thing- it really helped! I hardly know anything about particle physics- would you mind explaining how protons are made of "a massive mess of quarks"?

So if I said, in very very simple terms, that there are many different combinations of quarks and leptons that make up different particles (mesons and baryons), which, in turn, make up stuff like elements, would I be wrong? Does that mean that yes, element-like combinations do exist but they simply just aren't called elements?

Thank you again!
(edited 9 years ago)
Reply 6
Original post by uberteknik
Elements are defined by the number of protons in the atoms nucleus. Isotopes of any given element have a different number of neutrons in the nucleus.

Neutrons have two down and one up quark. Neutrons convert to protons during beta-decay (producing a new element) and at the same time o producing an electron and anti-neutrino.

Protons convert to neutrons by the absorption of a W- boson.

These tables summarise the different combinations:

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/baryon.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/meson.html#c1


(This is in my reply to lerjj as well, hope you don't mind but-)
So if I said, in very very simple terms, that there are many different combinations of quarks and leptons that make up different particles (mesons and baryons), which, in turn, make up stuff like elements, would I be wrong? Does that mean that yes, element-like combinations do exist but they simply aren't called elements?

Thank you!
(edited 9 years ago)
Reply 7
Original post by fizzers
Thank you for the detailed answer especially for pointing out the 'uud' thing- it really helped! I hardly know anything about particle physics- would you mind explaining how protons are made of "a massive mess of quarks"?

So if I said, in very very simple terms, that there are many different combinations of quarks and leptons that make up different particles (mesons and baryons), which, in turn, make up stuff like elements, would I be wrong? Does that mean that yes, element-like combinations do exist but they simply just aren't called elements?

Thank you again!


Mesons and baryons don't contain leptons, only quarks. Atoms contain protons, neutrons and electrons, because everything else decays to those particles very rapidly. Even neutrons are only stable when in nuclei.

So no, you don't get element like combinations purely because they'd be horrifically unstable. You wouldn't even be able to make them I expect because they'd probably decay before the whole system could be together for long enough to actually be an 'atom' rather than just a bunch of exotic particles flying past each other.

You can, however, get anti-atoms. You can make anti-Hydrogen using positrons and antiprotons, but again it's fantastically difficult (but stable if you ignore the fact that antimatter annihilates on contact with matter).
Reply 8
Original post by lerjj
Mesons and baryons don't contain leptons, only quarks. Atoms contain protons, neutrons and electrons, because everything else decays to those particles very rapidly. Even neutrons are only stable when in nuclei.

So no, you don't get element like combinations purely because they'd be horrifically unstable. You wouldn't even be able to make them I expect because they'd probably decay before the whole system could be together for long enough to actually be an 'atom' rather than just a bunch of exotic particles flying past each other.

You can, however, get anti-atoms. You can make anti-Hydrogen using positrons and antiprotons, but again it's fantastically difficult (but stable if you ignore the fact that antimatter annihilates on contact with matter).


Sorry for the awfully late reply! This explained a lot- thank you!
I would ask why antimatter 'annihilates on contact with matter' but I reckon I could and should probably read up and familiarise myself with all the basics before! :smile:

Quick Reply

Latest