Re: Is there a maximum atomic number?

Hi Isaac,

Yes, there is a maximum atomic number for a single atom. The reason comes from nuclear physics. A nucleus can have no more than 126 protons (and around 150 neutrons), because a nucleus with more than approximately 126 protons cannot possibly hold itself together.

First of all, remember your basic atomic structure: all of the protons and neutrons are extremely extremely close together in the middle of the atom. All of the electrons are orbiting far away (a hundred thousand times farther apart than the protons). The "atomic number" is just a count of the number of protons in the nucleus. If there is an upper limit to the number of protons in a single nucleus, then this is also an upper limit on the atomic number of this atom.

Second, remember your basic laws of static electricity: Like charges repel. The closer two charges are, the more strongly they'll repel one another. Protons all have positive charge (i.e. they are all "like charges"); moreover, in the nucleus they are packed very close together. If you put more than 126 protons together into one nucleus, they just repel one another so strongly that nothing can hold them together, not even for a microsecond. The nuclear force (called the "strong force"), which holds smaller nuclei together, is not strong enough across the width of these bigger nuclei.

Nobody is quite sure about the stability of nucleus #126, even, since it has not been made yet. Everything above lead (#82) is somewhat unstable; everything around and above hahnium (#105) is extremely unstable. Nuclei like #121 or #123 are so unstable, we think, that they can never really be said to form at all. #126 (for various theoretical reasons) may be an "island of stability", but around and beyond that, all nuclei are expected to just fall apart due to electrostatic forces. They end up undergoing "spontaneous fission", wherein half of the nucleus just repels the other half so strongly that they fly apart. If you can't make that nucleus, you can't make that atom.

The maximum atomic number observed so far is #114. There was an announcement that Berkeley Lab created #118, which decayed into #116, but the supposed "detection" seems to have been an experimental mistake. Unless the theories are dramatically wrong (and so far there is no whisper of them being wrong - they pretty correctly predict things like the lifetime of #114 et. al.) everything above #126 will be irredeemably unstable.

I hope this is a bit clearer than my previous response to this question? :) If you really do want an third-party, independent opinion, please let us know.

-Ben

P.S. I ought to mention, for completeness' sake, that particle physicists have theorized about something called a "strangelet". A strangelet is a little blob of matter which in some ways behaves like a nucleus, but does not really contain protons or neutrons. A strangelet can be arbitrarily heavy, large, and charged ... the lower limit may be something like 10,000 proton masses, and the upper limit is something like an entire neutron star. If strangelets really exist, you can put some electrons around them and call them "strange atoms" with "atomic numbers" ranging from 1000 up to 10 billion billion billion. But they would have very odd properties indeed. And, it must be emphasized, they are predicted by some theories, and have never been observed, and so may not exist. I think they are interesting, because I am actually building an experiment that will look for them in space. If this is the sort of thing you're looking for, try a Web search (or ask us another question) specifically about "strangelets".