This update is embedded within a detailed analysis of Lavelle’s abortive 2008 attempt to discredit this suggestion.
In 2016, an IUPAC task force was instituted to endeavor to resolve definitively which option would be given official IUPAC status [17]. Toward this endeavor, Scerri and Parsons have compiled their own account and recommendations [18].
Some Aspects of the Group 3 Debate
The complexities of the debate would fill a volume on its own. Only some of the key issues will be addressed here. It was unfortunate that the first modern contribution to the discourse, that by Luder, was published in the obscure and long-deceased journal, Canadian Chemical Education [3]. In the article, he used two (innovative) 32-column Periodic Tables to show that, by placing lanthanum and actinium in Group 3, Group 3 then became separated from the d-block elements. Instead, it was isolated next to the Group 2 elements. On the other hand, placing lutetium (lawrencium being then unknown) as the third member of Group 3, ensured that these elements became placed next to Group 4. Luder considered the second option the only logical placement. The two options are shown in Figure 4.2.
Physical Properties as Criteria for Location
Jensen’s 1982 article [2] raised some interesting points about chemical compatibility. Three of the criteria he chose were atomic radii, the sum of the first two ionization energies, and the melting point. He compared the two options of Sc–Y–La and Sc–Y–Lu with the subsequent d-block sequences of Ti–Zr–Hf, V–Nb–Ta, and Cr–Mo–W (Figure 4.3).
In terms of atomic radii, the early transition metals show a systematic pattern of an increase from 4th Period to 5th Period, then a decrease to the 6th Period. This decrease is a result of the so-called “lanthanoid contraction” (see Chapter 12). The Sc–Y–Lu series follows this pattern, while the atomic radius of lanthanum is larger than that of yttrium. There is an inverse pattern with the sum of the first two ionization potentials, but then this would be related to atomic radius and is not surprising. For the melting point, the trend is not so precise, though the Sc–Y–Lu series does show an increase (as do the transition metals), while the Sc–Y–La series shows a decrease. From these data, Jensen noted that scandium and yttrium better matched with lutetium. Hence Group 3 was better considered as Sc–Y–Lu–Lr.
Figure 4.2 The two possible locations for Group 3 according to Luder (Ref. [3]).
In addition to the numerical data, Jensen provided some comparative properties, three of which are shown in Table 4.1. A large range of properties are common to all rare earth elements, but Jensen found a few specific examples where the properties of lanthanum differed from those of scandium, yttrium, and lutetium. Again, he concluded that the better fit was Sc–Y–Lu–Lr.
Figure 4.3 Diagrams comparing properties of Group 3 “candidates” to those of early transition metals (adapted from Ref. [2]).
Table 4.1 Some comparative properties of scandium and yttrium with lanthanum and lutetium (adapted from Ref. [1])
Endeavoring to identify the key features of the debate, Lavelle’s position largely related to electron configurations of the atoms. He argued that as atoms of neither lanthanum nor actinium possessed an electron in an f-orbital, instead possessing an electron in a d-orbital, then both elements needed to be considered as members of the d-block [6]:
However, placing lanthanum (La) and actinium (Ac) in the f-block is the only case where a pair of elements is placed in a group that results in their being part of a block with no outer electrons in common with that block.
This is shown in Table 4.2, together with the other relevant electron configurations.
The debate discussed in the previous section revolved largely around the relevance of placement of an element upon its ground-state electron configuration. For example, Laing noted that f-block member thorium has instead a ground-state configuration of [Rn]7s26d2 [12]. The unexpected electron occupancy of a 7p orbital for lawrencium (see Table 4.2) seemed to cause a particularly bitter exchange on the relevance of orbital occupancy for Group 3 membership. In conclusion, though certainly not in closure, to match the d-block electron configurations (Table 4.3), it would seem most logical to identify the Group 3 elements as Sc–Y–Lu–Lr.
Table 4.2 Electron configurations for the competing elements for membership of Group 3
Table 4.3 Comparative electron configurations for the Group 3 (inc. Lu and Lr), Group 4, and Group 5 elements
Commentary
In Chapter 5, the term “rare earth metals” will be introduced. By definition, this set of chemical elements includes scandium, yttrium, and all of the elements from lanthanum to lutetium inclusive. Thus, any decision of the membership of Group 3 does not affect the identity of the rare earth metals.
The membership of the f-group elements known as the lanthanoids will be affected, depending upon the definition of Group 3. There is no conflict if all 15 consecutive chemical elements are chosen, which have a common +3 ion charge and which are found in similar ores. Likewise, the actinoids will be a 15-member series. However, if the lower members of Group 3 are excluded from a “double membership” in the appropriate f-block series, then complexities will follow.
In this book, therefore, to avoid placing either of La–Ac or Lu–Lr in both Group 3 and in the f-series in an 18-column Periodic Table, the lower placements in Group 3 will be left empty. It is more important (in this Author’s view) to populate the f-series with 15 members and show the continuity of their properties.
References
1.L. S. Foster, “Why Not Modernize the Textbooks Also? I. The Periodic Table,” J. Chem. Educ. 16(9), 409–412 (1939).
2.W. B. Jensen, “The Position of Lanthanum [Actinium] and Lutetium [Lawrencium] in the Periodic Table,” J. Chem. Educ. 59(8), 634–636 (1982).
3.W. F. Luder, “The Atomic-Structure Chart of the Elements,” Can. Chem. Educ. 5(3), 13–16 (1970).
4.R. W. Clark and G. D. White, “The
