A very widely held belief, among chemists and others alike, is that the periodic system consists primarily of a classification of the elements as simple substances that can be isolated and whose properties can be examined experimentally. However, there is a long-standing tradition of also regarding the elements as unobservable bearers of properties, sometimes elements as basic substances.
Figure 3.8 The Rich and Laing proposal showing hydrogen as a member of Group 1, Group 14, and Group 17 (see Ref. [20]).
Figure 3.9 The placement of hydrogen according to Kaesz and Atkins (see Ref. [21]).
To summarize Scerri’s critique of Kaesz and Atkins, Scerri believed that the Periodic Table represented the order of atomic structure, not any bulk chemical behavior.
… And Then There Is Helium
Though most of the discussions have centered upon the location of hydrogen, the location of helium has also been contentious.
Hydrogen as a Member of Group 1 and Helium as a Member of Group 2
Up to this point, we have only considered the possible locations of hydrogen in isolation. The arguments were largely, but not entirely, on chemical grounds. If the Periodic Table arrangement is defined by the electron configuration, then logic demands that hydrogen, 1s1, and helium, 1s2, are placed as the top members of Groups 1 and 2, respectively. One of the Periodic Table designs by Janet in 1928 [23] followed this logic. Then in 1934, White authored a modern-style Periodic Table (reprinted by Laing [24]) displaying electron configurations to reinforce the reason for the design (Figure 3.10).
The first thorough modern discussion of this possibility was given by Katz [25]. In the article, Katz first described moving “He” to above “Be,” then shifting Group 1 and Group 2 to the right-hand side of the Periodic Table to generate the left-step (or right-justified) Periodic Table shown in Figure 3.11.
As Katz and, later, Scerri [26] have commented, the left-step table is more elegant than the conventional table. Also the orbitals are now in sequence as f>d>p>s instead of s>f>d>p. The complicating factor arises from electron configuration considerations.
Figure 3.10 The first three Periods of White’s 1934 spectroscopic-based Periodic Table (reprinted in Ref. [24]).
Figure 3.11 The left-step Periodic Table (from Ref. [6]).
One may protest that helium is not a reactive metal. Bent was not swayed by such an argument. He believed that electron configuration — particularly using the left-step Periodic Table — was the essentiality: the Periodic Table is about atoms, nothing else [27]:
The answer given here to the Helium Question To Be or Not to Be? is, on both chemical and physical grounds, a resounding Yes! The most noble of the noble gases is not a Noble Gas. Helium’s natural position in Periodic Tables is in the s-block above beryllium …
Thus the debate becomes one of chemical properties versus spectroscopic energy levels. Novarro has cited a quote by Scerri that sums up the situation [28]:
Chemists may place He in the noble gas column, physicists however would rather place it above Be.
In the continuing debate, Ramíríez-Solís and Novarro used quantum-mechanical grounds to argue for helium’s place to be above neon [29]. Taking the contrary view, Grochala [30] noted that nothing is seen to be wrong in placing nonmetal hydrogen at the top of the Group 1 metals, so what objection can there be to placing helium also above a metal (beryllium)?
Hydrogen in Group 17 and Helium in Group 18 (Again)
More recently, Scerri has recanted his chemical heresy of placing helium in Group 2 [6]. By combining Period 1 and Period 2 in a single line, helium is safely returned to its chemical “home” atop the noble gases. Hydrogen, meanwhile, is given a home with the halogens, probably a more welcoming location for an element that exists in nature as a diatomic gas, not as a solid metal (Figure 3.12).
Figure 3.12 The revised Scerri left-step Periodic Table (from Ref. [6]).
Commentary
By 2010, the Editor of the Journal of Chemical Education felt that the hydrogen location debate had run its course. In an Editor’s Note, Pienta stated [31]:
… the Journal is implementing a new policy concerning submissions about the periodic table; those that cover new ground will be considered, but continuing arguments on longstanding issues will not be accepted for review.
As the purpose of this book is to look predominantly at the chemical aspects of the Periodic Table, the convention of placing helium as a member of Group 18 will be followed. For hydrogen, it is the Author’s prerogative to choose the location of hydrogen: that will be the Rang, and later Kaesz and Atkins, “lonely” central position.
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