# About limit for atomic number

Discussion in 'Physics & Math' started by Eagle9, Dec 21, 2010.

1. ### Eagle9Registered Senior Member

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As well-known the atomic number uniquely identifies a chemical element, for instance Hydrogen’s atomic number us equal to one, Uranium’s is equal to 92 and etc. I wonder, is there any limit for atomic numbers and hence the number of chemical elements? Let’s say, can there exist in nature the element with atomic number of 156 or 270? I know that creating them synthetically would be greatest challenge, but now I would like to know if they generally can exist or not

3. ### prometheusviva voce!Moderator

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Theoretically you could make any element with any atomic number but it will be unstable and will eventually decay into something stable that we already know about. This picture shows the stable elements - as you can see, the largest stable number of protons is Bismuth, having 83.

5. ### Fraggle RockerStaff Member

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They can exist, but as the number of protons increases, the half-life of the substance becomes progressively shorter. You'll eventually reach a point at which the half-life is so brief that you won't have any practical way to observe the atoms, much less test them.

7. ### mathmanValued Senior Member

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"Bismuth has classically been considered to be the heaviest naturally-occurring stable element. Recently, however, it has been found to be very slightly radioactive: its only naturally occurring isotope bismuth-209 decays via alpha decay into thallium-205 with a half-life of more than a billion times the estimated age of the universe."

Above is from Wikipedia article.

8. ### prometheusviva voce!Moderator

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When you're talking about those sorts of timescales I bet there's a bunch of other "stable" nuclides that turn out to be unstable. In field theory, there aren't really any stable particles at all. A real particle is just a virtual particle that is very close to being on shell for a while.

9. ### TachBannedBanned

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The protons in the nucleus are kept together by the strong force. On short distances , the strong force can overpower the enormous electromagnetic force that makes protons repel each other.
As you start "packing" more protons and neutrons in the nucleus, the distance needed to be covered by the strong force increases and the electromagnetic force starts overpowering the strong force. As such, the nucleus created by packing more and more nucleons together is no longer stable. This is why we cannot synthesize infinitely heavy elements.

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11. ### mathmanValued Senior Member

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There is no evidence for your assertion, so I'll continue to assume all known stable isotopes are truly stable.

12. ### prometheusviva voce!Moderator

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Indeed. My limited understanding of nuclear physics is that it's quite ad hoc and in fact quite poorly undertood. A lot more so than, for example, atomic physics which is more or less tied up by the Schrodinger equation.

13. ### FarsightValued Senior Member

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When I look at isotopes I tend to think of the nuclear force as "neutron linkage".

14. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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This doesn't make sense.

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16. ### BenTheManDr. of Physics, Prof. of LoveValued Senior Member

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This sounds a bit like numerology, and I don't know if it's right. It may be that the patterns you're noticing have already been documented, you might try looking at the nuclear shell model.

17. ### FarsightValued Senior Member

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They haven't AFAIK, though that's not to say they aren't in papers somewhere that have received scant publicity. What does seem to get publicity is nuclear-shell-model "magic numbers". I have to say that sounds more like numerology than the neutron-linkage inference drawn from atomic number and atomic weight.

18. ### Captain KremmenAll aboard, me Hearties!Valued Senior Member

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Menages a trois are notoriously unstable.
Often the neutron will love one proton more than the other, and just want the other as a friend.
This causes jealousy between the protons, and often leads to tragic consequences.

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and the distance needed to be covered by the weak force decreases.

20. ### rpennerFully WiredValued Senior Member

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Foul. What does the weak force have to do with internucleon forces?