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Bifold symmetry in the metal-nonmetal progression

I finally believe I've nailed this, not for posting to Wikipedia, but to go into a journal:

		Noble gases He, Ne, Ar, Kr, Xe, Rn
Active metals Groups 1–3, Ln, An, (Al)			Corrosive nonmetals O, F, Cl, Br, I
Transition metals Most of groups 4–11			Related nonmetals H, C, N, P, S, Se
Frontier metals (Al), Ga, Bi etc			Metalloids B, Si, Ge, As, Sb, Te
		Noble metals Ru, Rh, Pd, Ag, Os, Ir, Pt, Au

The category name related nonmetals is analogous to older references to the transition metals as related metals, for example:

• Ebel IL 1938, "Atomic structure and the periodic table", Journal of Chemical Education, vol. 15, no. 12, p. 575
• Quagliano JV & Vallarino LM 1969, Chemistry, Prentice-Hall, 3rd ed., Englewood Cliffs, NJ, p. 848
• Luder WF 1970, "The atomic structure chart of the elements," Canadian Chemical Education, April, p. 13

This category name also refers to the fact the related nonmetals tend to form covalent bonds with metals. Here the word "related" is associated to "covalent", as follows: covalent→shared→related.

The related nonmetals are related by, among other things, the H-C-P-N-S-Se thread.

It's a pleasing coincidence that the transition metals line up with the related nonmetals.

I'm eschewing the term post-transition metal so as to not have to deal with the question of Al, or perhaps I should move it into the active metals category?

Praise be that all category names are relatively short.

The balanced 6-6-5-6 distribution of the nonmetals is pleasing.

-- Sandbh (talk) 12:00, 7 September 2019 (UTC)

Interesting. I just corrected At ---> Ar for the noble gases, unless astatine is somehow a noble gas in this element scheme. ― Дрейгорич / Dreigorich Talk 10:40, 10 September 2019 (UTC)

Electronegativity

Electronegativity bars for element categories

This chart has blue and red bars spanning the lowest and highest electronegativity values for each of the eight classes of elements.

There seems to be two kinds of bifold symmetry:

• The first is the y-axis symmetry for the noble metals and noble gases; and the frontier metals and metalloids.
• The second is the x-axis symmetry for the transition metals and metalloids; and active metals and corrosive nonmetals.

Do I have this right? It wasn't something I was expecting. Sandbh (talk) 12:38, 19 September 2019 (UTC)

---

From the 2.2 baseline, the noble metals and metalloids seem to be inversions relative to each other, and then the frontier metals versus the noble gases, if we just go by ranges over electronegativity.

1. Comparing the noble metals with the metalloids:

The noble metals begin to show some surprising nonmetallic behaviour e.g. Au sometimes behaves as if it were a halogen, and both Au and Pt are known to form anions e.g. in CsAu, and the Ba platinides (Ba₂Pt and BaPt).

The metalloids, while they are chemically weak nonmetals, show the most metallic character among the nonmetals. For example, on the analogy between B and metals, Greenwood (2001, p. 2057) commented that:

The extent to which metallic elements mimic boron (in having fewer electrons than orbitals available for bonding) has been a fruitful cohering concept in the development of metalloborane chemistry…Indeed, metals have been referred to as "honorary boron atoms" or even as "flexiboron atoms. The converse of this relationship is clearly also valid…

Sb and even Ge are sometimes referred to as metals.

2. For the frontier metals and the noble gases:

The heavier (period 6) frontier metals border on nobility:

Because of the increase of nuclear charge across each of the transition series, the B metals are distinguished from the early A metals by their much weaker tendency to form ions or to form compounds with the non-metals…This feature is particularly marked in the final row of B metals, Au, Hg, Tl, Pb, Bi, and Po…where the nuclear charge has been built up across the lanthanide as well as the third transition series. In some respects these elements might almost be classed as super-B or C metals. (Phillips and Williams 1966, p. 459)

The noble gases become more metallic going down the group, so much so that Rn begins to some cationic behaviour (cf At).

• Phillips CSG and Williams RJP 1966, Inorganic chemistry, vol. II, Clarendon Press, Oxford University Press, Oxford
• Greenwood NN 2001, 'Main group element chemistry at the millennium', Journal of the Chemical Society, Dalton Transactions, issue 14, pp. 2055–66

Sandbh (talk) 01:36, 20 September 2019 (UTC)

Group: n/a

In {{Periodic table (group names)}} (article Group (periodic table)), I have added footnote "n/a" because somewhere we better mention this PT habit. That blank group number looks strange to outsiders. -DePiep (talk) 22:06, 1 October 2019 (UTC)

One these columns fill up, I wonder what nomenclature we'll use in the future. I just refer to them as "cerium and thorium", "praseodymium and protactinium", etc. for now. I'd maybe say they're an "inner group 3" and number them something like 3-I, 3-II, 3-III... 3-XIV (or some other convention), but I know many would disagree. They don't really form groups for now, but it is a question we might have to think about one day. ― Дрейгорич / Dreigorich Talk 03:35, 2 October 2019 (UTC)