I give my students taking freshman chemistry an on-line quiz every week. After the week in which we discussed groups of elements, one of the questions had to do with identifying and naming all of the elements in a particular group, in this case, group 4A (or group 14 in the IUPAC designation). This is the group headed by carbon, which also includes silicon, germanium, tin and lead. One of my students contacted me because she kept getting the answer wrong to this question. The problem? She was including flerovium in the list. I thought “What the hell is flerovium?” And then I remembered that the 7th row of the periodic table had been filled out recently with newly discovered superheavy, radioactive elements. I checked a latest-edition periodic table, and sure enough, flerovium (element 114) was at the bottom of group 4A. I responded to the student that the on-line quiz simply hadn’t caught up with the latest version of the periodic table (and I hadn’t either).
I’m not really much of a fan of the efforts to create new superheavy elements because, it seems to me, that these elements are of limited use. They decay radioactively to other elements in very short periods of time, and if you manage to make 30 atoms of said element, that’s considered quite a lot. With such small quantities and such short lifetimes, there isn’t enough time to determine the element’s physical or chemical properties. As such, these elements are really of academic interest only. But there is one aspect I do find interesting as a reason for pursuit of their study, and that’s to test the theory of the “island of stability” hypothesized to exist among the superheavy elements.
Way back when I took freshman chemistry, now more than 40 years ago, we very briefly covered the expansion of the periodic table by human-made elements. The heaviest element found on Earth naturally is uranium (element 92). However, all elements heavier than bismuth (element 83), including uranium, are radioactive and will eventually decay to lighter, more stable elements. In the 1940s, nuclear chemists discovered that it was possible to make elements heavier than uranium, though these were all guaranteed to be radioactive, with lifetimes getting shorter the heavier they got.
However, it was observed that not all of the elements lighter than bismuth are equally stable, and that the most stable elements occur at particular “magic numbers” of protons and neutron. The elements that correspond to these magic numbers are Helium (element 2), oxygen (element 8), calcium (element 20), nickel (element 28), tin (element 50), and lead (element 82). A theory was developed to try to explain this behavior, called the shell model, where a magic number corresponded to the filling of a shell in the nucleus; a filled shell would confer greater stability to the nucleus. (Physicist Maria Goeppert Mayer created the model in the late 1940s and the early 1950s, and eventually shared in the 1963 Nobel Prize for Physics, only the 3rd woman to be awarded a Physics Nobel.)
Of course, there’s no reason for the “magic numbers” to give out at 82. Goeppert Mayer conjectured the next one would occur somewhere around element 114 or or so. This raised the possibility that, as nuclear physicists created increasingly heavier elements past uranium, the elements would eventually become less radioactive, and some around the next magic number might actually be stable. This was the concept of the “island of stability”—that somewhere among the superheavy elements, the radioactive lifetimes would get longer, possibly resulting in a stable superheavy element at some point.
And this brings us back to flerovium. The prediction for element 114 was that it was smack dab in the middle of the island of stability. So recently, an experiment was performed to carefully study the radioactive decay properties of this element in order to determine if its lifetime is any longer than its superheavy neighbors. Atoms of flerovium were created by shooting high-speed calcium nuclei at nuclei of plutonium 244. Thirty flerovium atoms were observed to decay, but there was no apparent increase in the stability of the nuclei of these atoms compared to other superheavy elements.
This doesn’t kill the idea of the island of stability. Scientists will continue to search of lifetime lengthening of the superheavy elements, but it’s somewhat discouraging that it doesn’t appear to be precisely where Goeppert Mayer predicted it to be.
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