While waiting for a tutorial, I was reading some of the posters that the department whose building I was in had put up, in this case chemistry. One of them was about the periodic table, and in particular about elements past a certain proton number (I think that’s correct). It stated that once you get past a certain number, around 100, I think, the elements are no longer stable, however it is widely believed that once you get to around 125, there will be a “sea of stability”, although it is unknown whether we will ever be able to reach this.
Why is this sea of stability predicted and is it a widely held belief amongst chemists and physicists? Note: the numbers are from memory, so I don’t think that they’re very accurate.
Technically, it’s islands of stability, in a sea of unstable nuclides.
In point of fact, two or more protons can only coexist within a nucleus in the presence of neutrons that serve to stabilize them in immediate proximity to each other. For I believe every nuclide but “protium” (H-1) and “tralphium” (He-3) the number of neutrons is at least 100% of the number of protons, and for anything beyond Iron-56, there must be more neutrons than protons for stability to occur. The acceptable percentage range climbs with increasing atomic number, and above Bismuth-209 no quantity of neutrons will totally stabilize a nucleus.
Nonetheless, relative stability (and relative commonness) occurs in nuclei with 2x[sup]y[/sup] protons and the appropriate number of neutrons for that point on the periodic table. There are complex reasons for this which I don’t fully understand. The “islands of stability” are predicted points on the periodic table above what we presently have discovered or synthesized where these characteristics occur.
Either way, actually. Bismuth-209 is the sole nuclide of the (nuclearly) heaviest stable element, atomic number 83. No. 82, lead, has four stable isotopes, but quite a few of the elements just below them are single-stable-nuclide ones. And elements #84-94 exist in one of three capacities: trace isotopes; the three metastable nuclides Thorium-232, Uranium-238, and Uranium-235; and breakdown products from the decay of those three.