About limit for atomic number

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

  1. Eagle9

    Eagle9 Registered Senior Member

    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 :)
  2. prometheus

    prometheus viva voce!

    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.

  3. Fraggle Rocker

    Fraggle Rocker Moderator

    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.
  4. mathman

    mathman Valued Senior Member

    "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.
  5. prometheus

    prometheus viva voce!

    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.
  6. Tach

    Tach Banned

    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.
  7. Farsight

    Farsight Banned

  8. mathman

    mathman Valued Senior Member

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

    prometheus viva voce!

    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.
  10. Farsight

    Farsight Banned

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

    BenTheMan Dr. of Physics, Prof. of Love

    This doesn't make sense.
  12. Farsight

    Farsight Banned

    All: start with helium-3 and you've got one neutron and two protons. To visualize this imagine walking down the street with a girl on each arm. Your arms are linked. In this analogy you are the neutron, hence "neutron linkage", and a menage-a-trois such as this can be stable. Think of helium-4 in terms of you and your good buddy walking down the street with your two girlfriends, all with arms linked. That's stable too. Apply the same simple logic to carbon, oxygen, iron, and other isotopes. The more protons there are the more opportunity for stable extra links. There may be patterns to this. For example thallium-180 has 81 protons and 99 neutrons, but doesn't decay to via mercury-180 to two atoms of zirconium-90. Instead we see ruthenium-100 and krypton-80. Divide the 81 protons and 99 neutrons by 9 and you see they're in a 9:11 ratio. Then split the 9 into a 5 and a 4 and scale back up to 100 and 80, and note that flourine has an atomic number of 9. Hence thallium-180 might be akin to an aggregation of 9 flourine-19 atoms with 9 extra links. Interesting stuff.
  13. BenTheMan

    BenTheMan Dr. of Physics, Prof. of Love

    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.
  14. Farsight

    Farsight Banned

    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.
  15. Captain Kremmen

    Captain Kremmen All aboard, me Hearties!

    That's a bad analogy.
    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.
  16. and the distance needed to be covered by the weak force decreases.
  17. rpenner

    rpenner Fully Wired

    Foul. What does the weak force have to do with internucleon forces?
  18. The strong force can not overpower the strong force itself. It needs Energy from an outside influence (hence weak force). Not only does packing more protons into the nucleus increase its distance needed to be covered by the strong force, but decreases the distance to the weak force making it more ceceptabne to instability and the electromagnetic force that overpowers unstable elements.

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