The location and composition of Group 3 of the periodic table
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The location and composition of Group 3 of the periodic table René E. Vernon1
© The Author(s) 2020, corrected publication 2020
Abstract Group 3 as Sc–Y–La, rather than Sc–Y–Lu, dominates the literature. The history of this situation, including involvement by the IUPAC, is summarised. I step back from the minutiae of physical, chemical, and electronic properties and explore considerations of regularity and symmetry, natural kinds, and quantum mechanics, finding these to be inconclusive. Continuing the theme, a series of ten interlocking arguments, in the context of a chemistrybased periodic table, are presented in support of lanthanum in Group 3. In so doing, I seek to demonstrate a new way of thinking about this matter. The last of my ten arguments is recast as a twenty-word categorical philosophical (viewpoint-based) statement. Keywords Group 3 · Lanthanum · Lutetium · Descriptive chemistry · Isodiagonality
Scope My focus is intended to be philosophical or systematic rather than descriptive or theoretical. Along the way some more detailed ancillary arguments will be encountered where I feel these are required to provide context, are novel, or provide useful insights. Arguments in support of lutetium in Group 3 have been summarised by Scerri and Parsons (2018); Scerri (2020a, pp. 392–403); and Scerri (2020b). Landau and Lifshitz (1958, pp. 256–257) argued for group 3 membership of Lu on the basis of its complete 4f subshell. Scerri (2015, pers. comm., 9 December) referred to this as “one of the oldest categorical statements in favor of Sc Y Lu Lr”. Please refer to the Appendix to this paper for a commentary. I mention some recent arguments, in passing. Stewart (2018a, p. 117) observed that an argument for lutetium in Group 3 was that the pth element in the f-block series, with the exception of Gd, has p (for place) f-electrons. In contrast, Wulfsberg (2006, p. 3) opined that: …valence electron configurations of atoms and ions are also important in predicting the periodicity of chemical properties. Since ions are more important than isolated Mention of electron configurations in this article are those of the free atoms, unless otherwise specified. * René E. Vernon [email protected] 1
Kingston, ACT, Australia
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gaseous atoms for nearly all atoms, and important ions have no anomalous electron configurations, there is little reason to worry students with anomalous electron configurations of atoms: we prefer to teach ‘characteristic’ electron configurations without anomalies in the occupancies of d- and s-orbitals in the transition elements or d-, s-, and f- orbitals in the inner transition elements. Thus, with lanthanum in Group 3, the number of f-electrons in the trivalent cations of the f-block elements corresponds perfectly with their position in that block. The series starts with Ce3+ as [Xe]4f1 and concludes with Yb3+ [Xe]4f13 and Lu3+ [Xe]4f14. Tsimmerman and Boyce (2019) argued for lutetium in Group 3 on the basis of the regularity of spin multiplicity, whi
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