Commentary On Three Different Extensions For The Periodic Table Of The Elements
JERIES A. RIHANI
Let us assume that the nuclei of the elements, including their corresponding atomic structure, beyond element 118 are experimentally synthesizeable. Let us further assume that the Aufbau Principle in its extrapolated form also holds and applies even at this highly unstable and complex nuclear and chemical stage. If these assumptions were granted then we could perhaps argue that since the periodic table of the elements in its extended form must continue to be an exact reflection of the electron configurations of all the elements, including the newly synthesized ones, it must also reflect our detailed understanding of the way the atomic orbitals (at the ground state) tend to become either half-filled or completely-filled orbitals, as a net result of seeking lowest possible energy levels. For example, we know that at certain appropriate instances or occasions, the d orbital, within any relevant electron period (electrons in orbitals very close in energy levels,i.e. 7s<5f<6d<7p or 8s<5g<6f<7d<8p), chooses to receive an electron from the s orbital within the same period in order to satisfy this tendency (as in the electron configurations of Cr, Cu, Mo, Ag, Au, Uuu?, Uhu?). By comparison, the f orbital, in seeking to satisfy the same tendency in similar occasions, chooses to receive this required electron from the d orbital, its closest in energy level within the same period (as in the electron configurations of Eu, Yb, Am, No, Uqp?, Upb?).
Now, here is the big question. What happens when it is g's turn in the period 8s<5g<6f<7d<8p? Should the g orbital, in seeking the same, receive this 'occasional electron' from d or from, its closest, the f? Or, for that matter, when it is h's turn in the period 10s<6h<7g<8f<9d<10p, should the h orbital, in seeking the same again, pick its 'occasional electron' from d, .. from f, or from, its closest, the g?
At this point in the developmental stage of the periodic table it is helpful to know that we can put aside the question regarding h and focus on g alone. In fact, finding the answer for g can undoubtedly help us extrapolate and predict the answer regarding h (theoretically at least)*.
As you can see, answering the question regarding g leads to two probable answers and, at this stage, we do not know which answer is correct (that is if any). Thus, if g behaves in a similar manner as f and needs (in certain instances or occasions) to acquire its 'occasional electron' from d, we have no objection to that since it is assumed that d has one electron available to offer as predicted in the extended periodic table suggested by Glenn T. Seaborg. On the other hand, if we believe that neighboring f may constitute a better alternative donor than d (since neighboring f is closer to g in energy level) then it becomes necessary to propose a different extension than Seaborg's and may be one like that suggested by Jeries A. Rihani. It is important to emphasize, however, that accepting any of these two choices is totally dependent on whether the 'occasional electron' is available in one or the other, i.e. on how the electrons initially configure.
In 1984, I made two layouts, on independent sheets of paper, for two different extended periodic tables corresponding to the two different possible answers for g suggested above. And instead of including both versions in the appendix of the two studies published by The Royal Scientific Society in Amman I included only one. I was hoping that someday this extended form might draw the attention of somebody interested in the same issue and perhaps initiate some sort of a debate in order to resolve the issue. Unfortunately, this debate has never been realized and the issue still stands unresolved.
Recently, however, Pekka Pyykko of the University of Helsinky, Finland, in a paper presented at the 150th anniversary of "Weltkongress Chemie" at Karlsruhe, Germany, proposed a different approach to extension. As an expert in relativity and quantum chemistry, he applied the Dirac-Fock calculations on atoms and ions, up to atomic number 172, and showed, after taking into account the lower and higher spin-orbit split components of 8p and 9p, that the exterior shell-filling sequence for the period of elements 119-172 should roughly follow the order shown below:
Note that this exterior energy order is different from the corresponding one in the extrapolated Aufbau Principle(i.e. 8s<5g<6f<7d<8p), and suggests an extension very different from the extensions indicated previously. And to compare Pyykko's Extended Periodic Table, which is the most recent, with the others, you need to go here:
*Reaching the h-block stage is highly improbable and it seems likely the periodic table may reach an end at a much earlier stage either at atomic number 120 or 170.
[THE ABOVE COMMENTARY, OCCASIONALLY EDITED, MODIFIED AND UPDATED, WAS ORIGINALLY TAKEN FROM AN E-MAIL, SENT ON AUGUST 5, 1999, TO DR. HISHAM B. GHASSIB, THE ROYAL SCIENTIFIC SOCIETY, AMMAN, JORDAN.]