Those four new elements

The recent announcement of the official ratification of four super-heavy elements, with atomic numbers 113, 115, 117, and 118, has taken the world of science news by storm. It seems like there is an insatiable appetite for new information about the elements and the periodic table within the scientific world and among the general public. Maybe it’s all about nostalgia and the fact that the periodic table is like an old friend to anybody who has ever taken any chemistry class whatsoever? Or maybe it has to do with the meme-like status that the elements, their symbols, and their table have achieved in recent years. The elements are everywhere.

One of the most repeated statements about the latest four elements, none of which have names yet, is that their discovery has brought about the completion of the seventh period of the periodic table. But this is not necessarily the case. In recent years a perfectly respectable and alternative periodic table that was first proposed in the 1930s has been making a comeback. This is the left-step periodic table proposed by the French polymath Charles Janet, which is being actively supported by many periodic table experts. This table is obtained by making two small changes to the conventional table. First the element helium is moved to the top of the alkaline-earth elements, on the basis of its two electrons, just as the alkaline earth elements have two outer-shell electrons. Secondly, the entire two-column s-block is chapped off the left side of the table and transported to the right edge. This very elegantly shaped left-step table shows greater regularity than the conventional table by featuring the repetition of every single period length including the first very short period of two elements.

Left step periodic table. Courtesy of Eric Scerri.

But to return to the new elements, the left-step table shows that the seventh period is not in fact complete even after the inclusion of elements 113, 115, 117, and 118. Only when elements 119 and 120 are created will it be true that this period is really complete. Of course most of the news articles have acknowledged that the ‘completion’ of the seventh period does not preclude the discovery of elements even heavier than element 118. The question is where does it all end? The predictions depend on just how one conducts the calculation. According to a simple argument that relies on Einstein’s theory of relativity the highest atomic number that can possibly be produced is 137. Alternatively, if one takes into account the finite size of the nucleus of the atom, the answer is either 172 or 173.

But there are many other interesting questions connected with the periodic table that were not even mentioned in the recent flurry of news articles. For example, in addition to asking about elements beyond number 118, one might ask about the possibility of elements lying somehow within the current range of elements? This question is not as far-fetched as it might seem. There are many serious academic studies that have considered the possibility of quarkonium matter. Since a proton consists of three quarks it is not inconceivable that elements with atomic numbers increasing in units of one third, rather than by integral values, might actually exist.

But leaving aside such exotic species there is a great deal of debate concerning some very stable light elements such as hydrogen and helium. It has long been recognized that the element hydrogen could be placed at the head of the halogen group containing fluorine, chlorine, bromine, iodine and astatine. There is no clear-cut criterion that demands that it should be kept in group 1 of the periodic table. The case of helium has already been alluded to. In the left-step table this element is no longer regarded as a noble gas but should be placed into group 2.

Finally there is an ongoing debate concerning the membership of group 3 of the periodic table. Some periodic tables show the group as containing scandium, yttrium, lanthanum, and actinium while many others feature scandium, yttrium, lutetium, and lawrencium. Which version is more correct or indeed does it make sense to seek one objective correct version of the periodic table? At the same time that the International Union of Pure and Applied Chemistry (IUPAC) announced the ratification of the four new elements, they also approved the formation of a task force, led by yours truly, to discuss and make recommendations on the constitution of group 3 of the periodic table. Clearly the elements and the periodic table will continue to be in the news for some time to come.

Featured image: Elements Background. (c) Eyematrix via iStock.

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