User:Sandbh/Group 3

Cover sheet

Eric Scerri
IUPAC Task Group Chair
The Constitution of Group 3 of the Periodic Table

SUBMISSION TO TASK GROUP
1. I refer to your request for comments on this project, as advertised in Chemistry International, March–April 2016.

2. Please find attached a submission in support of Sc-Y-La-Ac. It comprises a list of arguments made in favour of Lu-Lr, and La-Ac. Many of these arguments have been made in the literature; others arose in the course of our deliberations or from contributions by other Wikipedia editors. We analyse each argument and make a finding as to its validity. We conclude our submission by comparing the overall case for the two options and explaining our support for Sc-Y-La-Ac.

3. One of us (Sandbh) thanks you for your help over the years in reading the e-mails I sent you on this topic and sharing your insights.

Thank you for the opportunity to contribute to your project.

Sandbh	Double sharp
Wikipedia editor   WikiProject Elements	Wikipedia Editor WikiProject Elements

Abstract

Drawing on the literature, arguments in support of Sc-Y-Lu-Lr are reviewed and analysed for their the validity. Most of these arguments are based either on group trends compared with other members of the d-block or similarities between Lu and Sc and Y. The same process is then applied to Sc-Y-La-Ac, in terms of basicity, condensed phase electron configurations, and the behaviour of group 3 as pre-transition metals. Judgements are made and elucidated about the strengths of the two sets of arguments. A conclusion is drawn in favour of Sc-Y-La-Ac.

Lu-Lr arguments

1956: Electron configurations (I) ♥

The Russian authors, Landau and Lifshitz (1977, p. 273–274) write:

The filling up of the 3d, 4d, and 5d shells…[has] a characteristic feature of [of] "competition" between the s and d states…The filling up of the 4f shell also occurs in a slightly irregular manner characterized by the competition between 4f, 5d, and 6s states…In books of chemistry, lutetium is usually placed in the rare-earth elements. This, however, is incorrect, since the 4f shell is complete in lutetium; it must therefore be place in the the platinum group… [They refer to Sc–Ni as the Iron group; Y–Pd as the Palladium group; and Lu–Pt as the Platinum group.]

They first wrote these words in 1956. Scerri (2015, pers. comm., 9 December) referred to them as "one of the oldest categorical statements in favor of Sc Y Lu Lr".

Analysis
The argument that a filled 4f shell in Lu forces its placement in the 5d transition metals is weak given that Yb also has a filled 4f shell. Such an argument would also seem to suggest that the group 11 and 12 elements, with their filled d-shells, must be grouped with the p-block elements in groups 13–18. However, group 12 is always considered a d-block group, since the ten columns from group 3 to 12 correspond to the filling of the ten vacancies in a d-subshell. Furthermore, the chemistry of group 11, with the d-electrons readily ionised, seems to further weaken such a possibility.

This suggests to us that the proper way to decide when a block ends is not where its shell is first filled, but when it first becomes chemically inactive. For instance, Cu and Zn both have a filled d-shell, but this is active in Cu and inactive in Zn, so that Zn is the true end of the d-block. Similarly, though Yb and Lu both have a filled f-shell, it is active in Yb and inactive in Lu, suggesting to us that Lu should similarly be taken as the last member of the f-block for consistency with the principles of the periodic table as it is drawn today.

1965: Similarity of Lu with Sc and Y ♥

A number of authors have argued that because Lu is more similar to group 3 than is La, it follows that Lu should be moved into group 3. For example:

• 1965: "In a widely-used version of the periodic table, lanthanum is classed in the same column with scandium and yttrium. However, in a number of respects lutetium resembles scandium and yttrium more closely than lanthanum does. Hence the periodic table should be modified so that scandium,yttrium, and lutetium are in the same column." (Hamilton)

• 1982: Jensen (as discussed later in this submission) partly relies on several similarities in the properties of Sc and Y versus those of Lu and La.

• 2014: "I based that comment on what I read in the Jensen paper (Eric's ref. 1). Apparently the methods of separating Lu from rare earths are the same as for Sc and Y but La is different - this is referenced to S I Levi's "The Rare Earths". The greater chemical similarity of Lu than La to the trends of that group and period is also referenced to T Moeller in "The Rare Earths" (ed. F H Spedding & A H Daane)." (McCaw)
  
  

Analysis
The nub of our critique of this approach is that we are not looking for something similar to Sc and Y but, rather, for something different from them that visibly continues the trend down group 3.

Similarity as a standard for placing elements represents something that not even the alkali metals and halogens can follow. For instance, lithium is anomalous in the alkali metals because of its small size and therefore much greater polarising power, and fluorine is anomalous in the alkali metals because of the great weakness of the F–F bond arising from the small size of the fluorine atom and the resultant repulsion between non-bonding electron pairs. Later in the d-block, mercury is very different from zinc and cadmium, being more strongly polarising and favouring 2-coordination as opposed to 4-coordination. In the p-block "all hell breaks loose" and we have nitrogen (a highly electronegative nonmetal) in the same group as phosphorus (a less electronegative one that can expand its octet) as well as arsenic and antimony (metalloids) and bismuth (a metal), and we certainly do not extract these elements in the same way. In fact Zn is more similar than Ca to Be and Mg, but that does not mean that Be and Mg should be moved to group 12 and placed above Zn. Asking for the third member of group 3 to act exactly like a carbon copy of its two "younger sisters" is asking for the impossible: this does not even happen in the alkali metals and halogens, the model examples of great group trends. In fact it is because they are model examples of great group trends that this does not happen: rather than a sameness throughout the column, there is a gradual change of properties–something we see everywhere across the table, whether we are going down the alkali metals or going across the lanthanide series.

Just because Lu is more like Sc and Y does not mean it should be in the same group with them. We do not necessarily place elements with each other just because of similarities. Shall we place Al in the same group as Be, or Mg in the same group as Li? Shall we place all the metalloids together in the same column? Obviously not! So why would we bend this for Lu? To do so would not be quite as bad since they share the same valence, but placing Lu under Y just for the sake of similar properties neglects the fact that as you descend a group, one does not expect properties of the elements to remain approximately constant. No, one expects increasing atomic radius, increasing basicity, and increasing electropositivity. Lanthanum continues these trends down group 3 while lutetium does not. Finally, this resemblance, weak as it is as an argument, is essentially limited to yttrium. Scandium is so much smaller than lutetium that it is qualitatively different, occupying an uneasy position in its chemistry intermediate between the heavy rare earths and the later 3d transition metals. No, we daresay it is better to consider the similarity of Y^III to Lu^III as just an effect of the lanthanide contraction, like the astonishingly similar size of Zr^IV and Hf^IV.

There is another flawed analogy in the periodic table. In the early 20th-century, when this kind of thinking led in our view to the erroneous placement of Lu under Y, there were also some chemists who placed Be and Mg over Zn (in group 12) instead of Ca (in group 2). Now indeed they do have similarities, but this is once again a size issue: Be and Mg show similarities to the class-B metals Zn, Cd, and Hg because of their small size compared to the obviously class-A metals Ca, Sr, and Ba. It is the same thing, just to a lesser extent, that occurs in group 3. There is a contraction in the heavier element due to the filling of an inner shell that brings its size and hence quantitative properties down to those of the lighter element; but since the consensus is to focus on trends instead of similarities, leading to Be and Mg being always placed above Ca today, it is the height of inconsistency to propose placing Lu under Sc and Y.

1967: f-like charge in La? ♥ ¶

The older literature has references to this possibility:

Matthias et al. (1967) attribute the melting point of La, which is much lower than would be expected from its periodic table position, to the presence of some f character, "in the hybridized wave functions describing the band structure for the valence electrons." Kmetko and Hill (1976) offer a theoretical explanation for this anomaly. They calculate a value of 0.6–0.7 for the amount of f-like charge in La (which agrees with Matthias et al.).

Liu (1980) observes as follows: "Lanthanum has a very high density of states at the Fermi level and a much higher superconducting critical temperature compared with other trivalent transition metals. These have led to speculation that the conduction bands at the Ferm level contain the f character. The band calculation of Glötzel and Fritsche(14) has shown that the f bands of La are above the Fermi level by about 2eV, but because of hybridization the occupied states contain 0.3 electrons of the f character for each atom." (p. 125)

Smith (1980) continues the theme:

"The existence of f states at or near the Fermi level is demonstrated by depressed melting points, by high low-temperature capacities, by the ability to make the solids either superconducting or magnetic in various intermetallic compounds, by the exterme sensititvity of most physical properties to pressure, and by the occurrence of certain unique crystal structures." (p. 39)

"…lanthanum, actinium, thorium, and americum…have some f character…These elements have f bands above the Fermi energy…The existence of these unfilled bands is shown, for example, by depressed melting points…by the double hexagonal close-packed (dhcp) structure of lanthanum and americium…and by the need for including some f character in the calculation of the Fermi surface of thorium." (p. 42)

"More specifically, the evidence for several pressure-induced phase transitions [in La] shows the f character in the bonding." (p. 43)

Analysis
After a flurry of speculation in the early 1980s literature, we were unable to locate any further references substantiating an f-like charge in La.

In any event, we are not impressed by these arguments given (1) there are other possible rationalisations for the low melting point and other properties of La—in fact one could argue that this is because of the lack of 4f character in La which limits 4f–5d hybridisation; and (2) "supervalent hybridisation" is known in Ca, Sr, and Ba as well, since CaF₂, SrF₂, SrCl₂, and all four BaX₂ are markedly bent in the gas phase and show sd hybridisation instead of sp hybridisation. But this is not at standard conditions, and we do not consider Ca, Sr, and Ba to be transition metals. The d-orbitals there may be able to act as the lowest unoccupied subshell in extreme circumstances, like the f-orbitals in La and Ac, but even they are too high to contribute usually. We assign elements to blocks based on what electrons are available for bonding, not for what other orbitals may occasionally make a contribution. Even when it was thought that PCl₅ implied d-orbital involvement for phosphorus, no one suggested that phosphorus was a d-block element.

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@Double sharp: I don't understand the point you're trying to convey with (1) and its reference to Th etc. Could you perhaps edit accordingly? Sandbh (talk) 03:47, 14 November 2016 (UTC)

This is from the various papers on the electronic structure of Th, given the reference to f-character of Th and Am that you quote. That is true, but not so for La and Ac. I agree its relevance is quite obscured the way I wrote it initially. The issue here is that although Th as [Rn]6d²7s² in the f-block might seem to be a valid precedent for putting Ac as [Rn]6d¹7s² in there as well, it is not so because Th has 5f involvement while Ac does not. But I think it is better said elsewhere, so I have deleted (1). Double sharp (talk) 04:10, 14 November 2016 (UTC)

BTW, it has been suggested (10.1063/1.476995) that the delayed collapse of the 4f shell is a relativistic effect (10.1063/1.476995): without it, you would expect 4f involvement to begin at La. (But then you would also expect 5d involvement to begin at Ba, so it is not clear what this means.) Double sharp (talk) 07:14, 15 November 2016 (UTC)

1982: Separation groups ♥

Jensen (1982, p. 634) writes, "For quite some time it has been known that Y, and, to a lesser degree, Sc are closer in their chemical properties to Lu and the other heavy rare earths than they are to lanthanum (1,2)…" The latter two references or notes read as follows:

(1) In the classical chemical methods for separating the rare earths Sc, Y, and Lu occur together in what is called the Y group, whereas La and Ac occur together in what is called the Ce group. See, for example, Levi, S.I.,"The Rare Earths," Longmans, Green and Co, London, 1915, Chap. IX.

(2) Moeller, T., "The Rare Earths", Spedding, F. H., and Daane, A. H., (Editors), Wiley, New York. 1961. Chap. 2."

Analysis
The fact that Sc, Y and Lu occur in the so called yttrium group, and that La and Ac occur in the "cerium" group does not imply anything particularly significant; it is simply a reflection of the increasing basicity of these elements as atomic radius increases. Thus, for another example, among the alkaline earth metals, Mg (less basic) belongs in the "soluble group" and Ca, Sr and Ba (more basic) occur in the "ammonium carbonate group" (Moeller et al. 1989, pp. 955–956, 958). Arguing that Lu should go under Y simply because they occur in the same chemical separation group ignores periodic trends. Moeller (1961, p. 10) in fact gives Sc, Y, La and Ac as the first members of the four "transition" series. Moreover, we could not find anything supporting Jensen's argument aside from a comment (p. 21) that the chemisty of Sc differs significantly from that of the "rare-earth elements" (La–Lu), something that is to be expected given the differences in radii. Similarly, Li is usually found with Mg and not with the heavier alkali metals Na and K; and Be does not occur together with Mg, Ca, Sr, and Ba.

---

"ignores periodic trends": the latter points cause some doubt on this. This could be justified if specified, but now it's too vague as a statement, I think.--R8R (talk) 17:45, 27 November 2015 (UTC)

Older tables ♥

Continuing on from the previous argument, Jensen (1982, p. 634) goes on to write, "…and on this basis alone a number of chemists in the 1920's and 1930's assigned Lu rather than La to group IIIB (3)." The latter reference reads as follows:

(3) See, for example, Shemyakin, F. M., Zh. Obshch. Khim., 2, 62 (1932) and Bury, C. R., J. Amer. Chem. Soc., 43, 1602 (1921). Further examples can be found in reference (14): Mazurs, E. G., "Graphic Representations of the Periodic System During One Hundred Years" Univ. Alabama Press, University, Alabama, 1974"

Analysis
Of the mentioned references:

• Bury shows Sc-Y-Lu on the basis of chemical properties, but does not elaborate which properties he had in mind. He draws an analogy to Be and Mg resembling Zn better than Ca.

• Mazurs has plenty of tables with Lu in group 3 as well as La-Ac tables pre-dating, dated during, and post-dating the 20s and 30s. One needs to be careful with Mazurs as some of his renderings of tables appearing in the literature are fanciful, but there is no doubting both kinds of tables have been around for quite a while.

• Shemyakin is a short article about placing the Ln into the 8-group table (noting Russian chemists are still keen on the Mendeleev's original format, not to say back in the 30s). It is mostly interesting from a historical perspective; it does not specifically discuss the group 3 problem, although it does very briefly mention "close similarities between Jt and Lu," without adding a word about it. The author suggests one would use, apart from the regular group 6a/6b notation, also 6a2/6a1 for lanthanides (Lu-Eu and Gd-Yb, accordingly), and nc and nd for what we would call group 9 and group 10. It does not cast much light onto the question.

• Furthermore, just because a classification has the weight of tradition behind it is not a good reason to use it. Many old tables from this time period also place Be and Mg in group 12 with Zn, Cd, and Hg.

Electron configurations (II) ♥

Jensen (1982, pp. 634–635) says that La and Lu have equal claims to the position under Y, based on their differentiating d electrons. He then asserts that nobody doubts Th is an f block element with an irregular electron configuration i.e. [Rn]6d²7s² and that this therefore "strongly" supports treating La i.e. [Xe]5d¹6s² and Ac i.e. [Rn]6d¹7s² as f block elements with irregular electron configurations. Thus Lu i.e. Xe4f¹⁴5d¹6s² and Lr i.e. Rn5f¹⁴7s²7p¹ fit under Y, with the result that each element in periods 6 and 7 of the d block has either a completed 4f¹⁴ or 5f¹⁴ shell.

Analysis
This is a weak argument. Firstly it is based on gas phase electron configurations which have little relevance to the chemistry of the elements. (We discuss gas phase v condensed phase electron configurations later in this submission.) Secondly, it seems to be only a "tipping point" argument. That is to say, if the merits of -La-Ac and -Lu-Lr are otherwise similar in terms of which one is placed under Y then, of course, -Lu-Lr would be the one given this would result in completed 4f¹⁴ or 5f¹⁴ shells across periods 6 and 7 of the d block.

Thirdly, though indeed nobody doubts that Th is an f-block element, this lack of doubt is quite probably due to the fact that the 5f orbitals demonstrably contribute in metallic thorium (being hybridised with the 6d and 7s levels), and that the electron configuration of the Th³⁺ ion is [Rn]5f¹, showing that the 5f orbitals are indeed low-lying here and available for chemistry. In contrast, the little evidence there is for purported f-orbital involvement in La and Ac is very spotty and inclusive. While slight irregularities in electron configuration are of course permissible and occur throughout the d- and f-blocks, it does not seem right to us that elements without any f-orbital involvement at all should be placed in the f-block.

Ionization potentials ♥

Citing the Russian chemist Chistyakov, Jensen (1982, p. 636) argues that the trend in the sum of the first two ionization potentials going down Sc-Y-Lu is similar to that occurring in groups 4 to 8, and unlike that of Sc-Y-La.

Analysis
True, but not the full story, and of questionable relevancy. Why the sum of the first two ionization potentials? In any event, the trend in this case (for Sc-Y-La) is similar to the trend seen in the group 2 and 1 metals, -Ca-Sr-Ba- and -K-Rb-Cs-. As well, the trend in the sum of the first three ionization energies for Sc-Y-La is a better fit with the trend occurring in groups 4 to 8, than is the case for Sc-Y-Lu.

The Russian source (English translation) is: Chistyakov VM 1968, "Biron's secondary periodicity of the side d-subgroups of Mendeleev's short table", Journal of General Chemistry of the USSR, vol. 38, no. 2, pp. 213–214.

The author compares the atomic radii and sum of the first two ionization energies (IE) for groups 3–8 and 11-12 and finds that Sc-Y-Lu is a better fit than -Y-La. He says this is probably due to the impact of the lanthanide contraction on the periodi 6 transition metals. For Group 11 he only uses the first IE's. In his conclusion he writes, "The radii of the free atoms, recently calculated from Dirac's equation, and the sums of the first two ionization potentials, i.e., parameters of the external ns-electrons of the d-elements, are periodic functions of the atomic numbers in each side d-subgroup." We thought his reference to "ns-electrons" explained why he was using the sum of the first two IE's rather than the first three (since it was group 3 that was the anomaly) but this doesn't work since, for example, Nb, Cr and Mo only have one s electron, so he isn't really comparing like with like as, to get the sum of the first two IE's for these metals he has to include one d electron each. And comparing the first two IE's of the group 11 metals fails to produce the pattern seen in the other groups, although admittedly doing so involves one s and one d electron for all three. We think this explains why Jensen left out the group 11 and 12 metals in his article.

Atomic radii ♥

Again citing Chistyakov, Jensen argues that the trend in atomic radii going down Sc-Y-Lu is similar to that occurring in groups 4 to 8, and unlike that of Sc-Y-La.

Analysis
True, but not the full story. The trend in atomic radii going down Sc-Y-La is instead similar to the trend seen in the group 2 and 1 metals, -Ca-Sr-Ba- and -K-Rb-Cs-.

Ionic radii ♥

Jensen (1982, p. 636) argues that comparisons in periodic trends favour Sc-Y-Lu.

Analysis
No data nor a reference is given. In contrast, Shriver and Atkins in their 4th edition, here and as extracted below, discuss ionic radius and its influence on chemical properties. Based on a data comparison, they say Sc-Y-La is a better fit than Sc-Y-Lu.

Problem 1.14

At various times the following two sequences have been proposed for the elements to be included in Group 3: (a) Sc, Y, La, Ac; (b) Sc, Y, Lu, Lr. Because ionic radii strongly influence the chemical properties of the metallic elements, it might be thought that ionic radii could be employed as one criterion for the periodic arrangement of the elements. Use this criterion to describe which of the sequences is preferred.

Answer

The common ionic state for the group 3 elements is +3, so the electron configurations for the elements in each sequence are:

Sequence (a)

Sc³⁺: [Ar] Y³⁺: [Kr] La³⁺: [Xe] Ac³⁺: [Rn]

Sequence (b)

Sc³⁺: [Ar] Y³⁺: [Kr] Lu³⁺: [Xe]4f¹⁴ Lr³⁺: [Rn]5f¹⁴

The electron configurations in sequence (a) are all rare gas configurations so the ionic radii should increase slowly as the principal quantum number, n, increases. In sequence (b), Lu3+ and Lr3+ also have filled f subshells. Since f electrons shield the nuclear charge so poorly, Z* is expected to be much larger for Lu³⁺ and Lr³⁺, thereby reducing the ionic radius. Thus, sequence (a) is preferred based on ionic radii. The measured ionic radii bear this conclusion out. For six coordinate radii, the values found are 0.885 Å for Sc³⁺, 1.040 Å for Y³⁺, 1.172 Å for La³⁺, and 1.001 Å for Lu³⁺.

Redox potentials ♥

Jensen (1982, p. 636) argues that comparisons in periodic trends favour Sc-Y-Lu.

Analysis
No data nor a reference is given. We had a look at the National Institute of Standards and Technology standard electrode potential data at http://www.nist.gov/srd/upload/jpcrd355.pdf but were unable to discern any meaningful differences in periodic trends between Sc-Y-La and Sc-Y-Lu, and neither choice results in a trend that is very similar to those of the neighbouring groups.

Electronegativities ♥

Jensen (1982, pp. 635, 636) argues that comparisons in periodic trends for Allred-Rochow electronegativity favour Sc-Y-Lu.

Analysis
True, but not the full story. The trend in going down Sc-Y-La is instead similar to the trend seen in the group 2 and 1 metals.

Further, the choice of electronegativity scale is a little arbitrary. Pauling clearly favours Sc-Y-La. Groups 1, 2, 4, and 5 have the period 6 element a hair more electropositive than the period 5 element; this works with La (1.1) under Y (1.22) but not with Lu (1.27) under Y.

Melting points ♥

Jensen (1982, pp. 635, 636) argues that the trend in melting points going down Sc-Y-Lu is a better fit with groups 4 to 10, than is the case with Sc-Y-La.

Analysis
True, but not the full story. The trend in melting points going down Sc-Y-La is instead similar to the trend seen in the group 2 and 1 metals, -Ca-Sr-Ba- and -K-Rb-Cs-.

Crystal structures (elements) ♥

Jensen (1982, p. 636) contends that the most compelling evidence for Sc-Y-Lu comes from the physicists. He says that, as a first example, the crystalline structures for Sc, Y, Lu are all hexagonal close packed (HCP) whereas that of La is double hexagonal close packed.

Analysis
The example given is true, but its relevance is questionable. For example, the structures of the group two metals Be, Mg, Ca, Sr, Ba, and Ra are HCP; HCP; face centred cubic; face centred cubic; body centred cubic; and body centred cubic. Groups 7, 8, 9, and 10 also show inconsistencies in crystalline structures.

We note, however, that in groups 7-9 we have a first-row anomaly between the 3d metal and the heavier two members whereas Sc-Y-La-Ac has the heavier elements be inconsistent, which is more akin to the situation in group 2.

Crystal structures (oxides, chlorides, various intermetallics) ♥

Jensen (1982, p. 636) says that the crystalline structures of the oxides X₂O₃ for Sc, Y and Lu are the same whereas that of La is different. The same pattern occurs with the chlorides -Cl₃ and various intermetallic compounds.

Analysis
True, but not relevant at least for oxides and chlorides. Different structures for homologous ionic compounds are unremarkable. Consider, for example, NaCl vs. CsCl (and this is for the alkali metals, the model example of great group trends). NaCl has the sodium chloride (rocksalt) structure; CsCl has a different (primitive) cubic structure, as shared with caesium bromide and caesium iodide, and many binary metallic alloys. When both ions are similar in size (Cs⁺ ionic radius 174 pm for this coordination number, Cl⁻ 181 pm) the CsCl structure is adopted, when they are different (Na⁺ ionic radius 102 pm, Cl⁻ 181 pm) the sodium chloride structure is adopted.

The reference to intermetallic compounds is from Hamilton (1965) who says, "There are at least several intermetallic compounds where the compound with La has a different crystal structure from the corresponding compounds with Sc, Y, and Lu." However, this is again not entirely unexpected because, as expected from its position in the next row down in the periodic table, lanthanum atoms are larger than scandium or yttrium atoms. It would therefore stand to reason that they should not be able to pack in a crystal structure in quite the same way as the smaller scandium, yttrium, or lutetium atoms.

• Hamilton DC 1965, 'Position of Lanthanum in the Periodic Table', American Journal of Physics, vol. 33, pp. 637–640

Excited state spectra ♥

Again citing Hamilton, Jensen says that the atomic spectra for Sc, Y, and Lu differ from La, in that for La, "excited energy levels have been observed which can be attributed to an electron in an f orbit" (Hamilton 1965 p. 637) whereas this is not the case for Sc, Y, or Lu thereby indicating, "that the 4 f wave function in La differs from the 4 f wave function in Sc and Y or the 5 f wave function in Lu; this causes the various line strengths to be different."

Analysis
OK, but incomplete. We have no primary grounds to query Hamilton's discussion about Sc, Y, Lu and La. However, we are troubled by Myers (1997, p. 201–202) who says that:

Normally we define transition metals as only those containing incompletely filled d shells but the empty d bands in the alkaline earths (Ca, Sr and Ba) and the filled d bands in Cu, Ag, and Au lie sufficiently close to the Fermi energy to produce significant effects, Because of this, the former group may be termed incipient transition metals, whereas the latter are immediate post-transion metals.

So, we tend to find Hamilton inconclusive as he does not say anything about the spectra of Ca, Sr, and Ba.

• Myers HP 1997, Introductory Solid State Physics, 2nd ed., CRC Press, Boca Raton, Florida

We would also draw some links between the situation in groups 2 and 3. Ca, Sr, and Ba are "incipient transition metals" with the empty d-bands close enough to influence spectroscopic properties as well as occasional supervalent hybridisation in CaF₂, SrF₂, SrCl₂ and BaX₂, so we also submit in the end that La and Ac are "incipient inner transition metals" with a similar usage of the f-bands. However, just as Ca, Sr, and Ba are not d-block elements and precede the d-block, so we argue that La and Ac should similarly be considered to precede the f-block.

Superconductivity ♥ ¶

Jensen (1982, p. 636) says Sc, Y, and Lu are not capable of superconductivity in bulk form at normal pressure whereas La is.

Analysis
Incorrect. Lu is capable of such conductivity. See http://arxiv.org/pdf/cond-mat/0410302.pdf

I've seen a paper (10.1080/00018736900101347) that (somewhat incoherently) argues for the opposite, that lanthanum's lack of 4f character is what allows it to exhibit superconductivity. From the abstract: "conduction electrons...participate in the superconductivity mechanism, while the 4f electrons tend to inhibit superconductivity". Consistent with this, cerium is not superconducting except at the high pressures needed to effect the 4f → 5d promotion (α→α′). However, lanthanum is superconducting and is the only rare earth metal to be so at standard pressures. It even notes that a 4f-type explanation of the low melting point of lanthanum predicts a valence of 2.29, which is at odds with the experimental result of 3. While the paper argues for 4f involvement in lanthanum, I find its argument very strange because it is against the "normal rare earths" from Pr to Lu (excluding divalent Eu and Yb and quasi-tetravalent Ce), which all have prominent 4f involvement. If La behaves differently from them you would expect the conclusion that it lacked something that Ce to Lu had, which might well be 4f involvement. Double sharp (talk) 06:34, 5 November 2016 (UTC)

P.S. Even more hilariously, they go on to write that Lu has the same conduction band structure as La; so you would expect that Lu would be a superconductor, unless there is enough 4f character to inhibit that. Since Lu is more reluctant (0.1 K) to be superconducting than La (6 K), this might imply that Lu actually has slightly more 4f character than La, which accords well with Sc-Y-La-Ac. Double sharp (talk) 06:39, 5 November 2016 (UTC)

Conduction band structures ♥

Citing Merz and Ulmer (1967), Jensen says that Sc, Y and Lu have conductivity bands with a d block like structure whereas La does not.

• Merz H & Ulmer K 1967, 'Position of Lanthanum and Lutetium in the Periodic Table', Physics Letters,, vol. 26A, no. 1, pp. 6–7
  
  

Analysis
We have no reason to question Merz and Ulmer's observation that La's conduction band does not have a typical d-block like structure. This may be associated with the presence in La of a low-lying nonhydrogenic (unoccupied) f-orbital. In any event, the significance of such an atypical structure is not clear to us since La still has the high density of states that are characteristic of transition metals (Goncharova & Il'ina 1984, p. 995). And while Lu may have a conduction band structure that is more characteristic of transition metals such as Hf, we do not think this is especially notable, since we generally expect the conduction bands of metals at or towards the end of the s-, d- and f-blocks, and some of those of the p-block metals (e.g. Sn, Bi, Po) adjacent to the metalloids, to be atypical for their blocks. We have commented elsewhere that similarity in properties is not necessarily the same as anticipated trends in properties, and we think this is another example.

We further note that x-ray isochromats of Gd to Lu suggest there is little to the story. Bergwall (1966) recorded these and found that they were rather constant, "which on account of the atomic configuration in these elements is expected." (p. 13) In other words, over half the lanthanides–not just lutetium—have conduction band structures that are more characteristic of transition metals such as hafnium! This means there is nothing particularly unusual about Lu being positioned in the f block and it may be that the atypical conduction band structure of La is no more than a one-off outcome of the imminent 4f collapse that will happen at Ce.

1996: f orbital participation in bonding? ♥

The literature contains references to this possibility:

From Dolg & Stoll (1996): "...the relatively small value of 0.04 Å for the lanthanide monoxides results from f-orbital participation in LaO, whereas the 4f shell has core character in LuO." (p. 626)

From MacKay et al. (2002), in their chapter on the Scandium Group and the Lanthanides: "The one case in which contributions to the bonding from the f orbitals is possible is in complexes of the heavier elements in which the coordination is high. Use of the s orbital, together with all of the p and d orbitals of one valency shell, permit a coordination number of nine in a covalent species. Thus, higher coordination numbers imply either bond orders less than unity or else use of the f orbitals. In addition, certain shapes (such as a regular cube) of lower coordination number also demand the use of f orbitals on symmetry grounds. These higher coordination numbers have only become clearly established recently, but their occurrence in lanthanide or actinide element complexes suggest the possibility of f orbital participation. Example include the 10-coordinate complexes mentioned above ["Yttrium, and the other lanthanides investigated, also form 10-coordinate M(NO)₃)₅^2– complexes…In Ce(NO₃)₆^3–, the coordination number is twelve…In the ion La(C₆H₉N₃)₄³⁺, the twelve nitrogen atoms form an almost regular icosahedron around the La atom."], LaEDTA(H₂O)₄ and Ce(NO₃)₅^2– or 10-coordinate La₂ (CO₃)₃.8H₂O; 11-coordinate Th(NO₃)₄.5H₂O (coordination by four bidentate nitrate groups and three of the water molecules; and the 12-coordinate lanthanum atoms in La₂ (SO₄)₃.9H₂O—with twelve sulfate O atoms around one type of La atom position."

From Sastri et al. (2003): "Two other polyhedra possible for 8-coordination are hexagonal bipryamid and cube...Cubic coordination requires f orbital participation and is a possible configuration for some lanthanide compounds. Some structures of lanthanide compounds with octa-coordination are given in Table 5.10." The example is given of LaTaO₄, with a cubic structure, although the column heading says nearest [italics added] regular shape. (pp. 397, 399)

From Zhang et al (2014): "Lanthanide ions have a strong ability to form complexes by the coordination bonding between their f orbitals and lone electron pairs of various Lewis bases. Therefore, TiO₂ doping with lanthanide ions can concentrate the organic pollutants at the semiconductor surface."

Analysis
The MacKay et al. argument seems to be weakened by the existence of 10-coordination in yttrium in [Y(NO₃)₅]⁻, since yttrium has the configuration [Kr]4d¹5s² with no possibility for 4f involvement. Thus 10-coordination cannot be taken to imply 4f involvement, even in the other lanthanides which form isostructural complexes. The symmetry grounds are also suspect: Greenwood and Earnshaw write in pp. 952–3 of the 2nd edition "The low symmetries of many of the above highly coordinated species [including extraordinary 9-coordinate Sc], which appear to be determined largely by the stereochemical requirements of the ligands, together with the fact that these high coordination numbers are attained almost exclusively with oxygen-donor ligands, are consistent with the belief that the bonding is essentially of an electrostatic rather than a directional covalent character". While f orbital involvement indeed must be invoked if high symmetry is present, it need not be the case for low symmetry.

As for possible 4f participation in exotic molecular species, it is interesting but surely does not force La to be an f-block element. In molecular CaF₂, there is some 3d participation from Ca, but Ca is not a d-block element. In contrast, the 3d shell is core-like in ZnF₂. Naïvely applying the same argument seems to lead to the conclusion that Be and Mg should be placed over Zn, which suggests to us that such arguments are not germane to the principles of the periodic table as it is most commonly presented.

Such bonds as Ca–F or La–O with their huge electronegativity differences are better described as ionic rather than covalent at standard conditions, so it is not surprising that they do not behave in a way characteristic of the rest of these elements' chemistry when they are forced to be covalent in the gas phase.

2005: Physical properties ♥

On the basis of 18 mainly physical properties Horowitz and Sârbu (2005) argue that Sc and Y are rather dissimilar to the lanthanides and that, since Lu is similarly an outlier among the lanthanides, it should be assigned to Group 3 as a homologue of Y.

Analysis
Among the lanthanides, Horowitz and Sârbu found that Pm, Dy, Tb, Nd and Ho could be regarded as "typical" lanthanides whereas Yb, Lu, Eu and La were outliers (p. 482). To some extent this finding does not surprise us since the typical lanthanides have mid-range lanthanide atomic numbers, whereas the outliers are found at either end of the lanthanide series. What does surprise us is that Horowitz and Sârbu appear to have "seized" on Lu—based solely on its outlier status—as their preferred homologue of Y absent of any consideration or comparison whatsoever of the merits of La, which was also identified by them as an outlier lanthanide, albeit not quite as peripherally. Jensen (2009; 2015, p. 25) has repeatedly argued for "verification of the validity of…group assignments through the establishment of consistent patterns in overall block, group and period property trends." When this is done for Lu and La, as set out elsewhere in this submission, we find a sound case for La, rather than Lu, as a homologue of Y. While Lu may be somewhat more of an outlier than La, the shortfall is insignificant in comparison to broader trends.

Another look

I read this article again, and again. The authors find that Sc and Y have properties rather dissimilar to those of the rest of the Ln (La to Lu) (pp. 480, 481) and that Yb and Lu are also appear to be outliers (p. 481). Among only the 15 Ln they find that Yb and Lu are outliers (pp. 482), followed by Eu and La (in order of outlier status) (p. 482). On this basis they assign Lu as a homologue of Y in group 3 (pp. 481, 482).

So they spent eleven pages rederiving the separation groups? (The groups are La, which is easily separated; Ce, which also is because of its tetravalence; the rest of the cerium group with Pr, Nd, and Pm; the redox-capable set Sm and Eu; the terbium group with Gd and Tb; the erbium group with Dy, Ho, Er, Tm; the redox-capable Yb; and then Lu in the "ytterbium group".) It is also well-known that Eu²⁺ and Yb²⁺ behave very similarly to Ca²⁺, Sr²⁺, and Ba²⁺.

The placement of Lu below Y is almost entirely based on the fact that its properties are more similar to those of Sc and Y, being largely intermediate between them. However, as I've said before, this ignores periodic trends, which do not expect properties to stay relatively constant down a group, but for there to be some sort of trend. So I would argue that one should not look as they did for an element that acted more like Sc and Y, but one that was to Y as Y was to Sc. When I check this against their table, I find that La continues the trends down from Sc and Y better than Lu. (Sc, Y, and La tend to be collinear in the plots, supporting this idea.)

Could I check what you've written in the first sentence of this para? The projection of the 17 Ln at Figure 12 (p. 480) shows Lu as being rather dissimilar to Sc and Y. (In fact it looks like Lu is instead closest to Er, Ho and Tm, its Ln predecessors, skipping Yb, which is about what I'd expect, and is consistent with our counter arguments to the Lu as a transition metal argument. Even the authors ack that, "As a rule, the highest similarity degrees appear for adjacent elements (in the sequence of atomic numbers)." (p. 481)) I looked again at Figures 9 to 12 (p. 480) and it seems that Y-La have a greater degree of similarity than do Y-Lu, if my trigonometry is right, based purely on the 18 properties in question I hasten to add. I do agree with the rest of the points in your paragraph. Sandbh (talk) 08:51, 9 November 2016 (UTC)

I was looking mostly at figure 9 and the individual values in the table. As Cotton has said, while Y is close to the heavy-lanthanide cluster, Sc is still really far out. I do agree that La is usually closer (Figs. 10 and 11), and you are right about that. (Though I would add that since none of the lanthanides are really that close to Sc and Y it is surely important to mention the argument on trends.) Double sharp (talk) 09:16, 9 November 2016 (UTC)

Also, I am really not surprised that La, Eu, Yb, and Lu are the outliers. Eu and Yb should of course be so because of their penchant for divalence (strikingly demonstrated in a density plot). Once you take out lanthanides like Ce, Sm, Eu, and Yb which can undergo redox reactions, of course La and Lu look strange; they're isolated! Double sharp (talk) 10:26, 8 November 2016 (UTC)

You know, why indeed should we be surprised with the results of their multivariate analysis. La starts the Ln; Lu is the last Ln. So, why would we expect much else apart from these two ending up as outliers? And the authors' typical Ln are Nd, Pm, Tb, Dy and Ho, which lie more or less evenly between La and Lu in the Ln atomic number sequence, much as expected. It's only taken a week for me to realise this. I'd now question why the authors appear to have "seized" on Lu as the best fit under Y, without looking at the other end of the Ln i.e. at La, seemingly absent of any consideration of the broader kinds of periodic trends we've been talking about. I suspect this line of thinking can form the basis of our academic critique of their argument. Sandbh (talk) 12:19, 11 November 2016 (UTC)

Calling Pm a typical Ln is very strange and partially a self-fulfilling prophecy. Firstly, it is absolutely not a typical lanthanide in the lab, because you almost certainly can't use it (I have, of course, never seen it). Secondly, I suspect most of its properties are derived from interpolation anyway, so they don't so much confirm a trend but assume it. But I agree with you on the rest. Double sharp (talk) 16:33, 11 November 2016 (UTC)

That's good. I'm not that concerned about Pm. Even the authors say their numbers for it need to be treated with caution (p. 482). Now, could you have a look at Laing's paper (2009) in JChemEd on the central role of gadolinium? The link is to the supplementary material version of the article, so should be open access. The more interesting items are the sentence at the top right of page 12 re La below Y, and footnote 2 on page 13. Laing says a reasonable case could be made for La below Y on the basis of comparing Ca-Sc, and Sr, Y, which is a weaker version of our argument comparing the vertical trends of Sc-Y-La with Sc-Y-Lu. It is pleasing to see that Laing recognises the worth of Sc-Y-La. Footnote 2 notes that Laing's way of organising the Ln is quite different from that of Horovitz and Sârbu. This is a little unfortunate since it kind of muddies the waters but I guess that makes our own argument of simply comparing vertical trends clearer. Sandbh (talk) 23:32, 11 November 2016 (UTC)

I can't access the supplementary material version, strangely, but I am quite pleased by what he says! I can not-quite-legally see the main two-page article about Gd, but not the rest of it. I think this goes to one of the other things I've said about the periodic table: it is only meant to give a first-order prediction of elements' properties, and if you want more details you need to take into account second- and third-order course corrections in the form of effects like the lanthanide contraction and singularities like the [Xe]4f⁷5d¹6s² configuration of Gd. (Although this does give me some motivation to make gadolinium a good article on WP.) Double sharp (talk) 02:28, 12 November 2016 (UTC)

Is there some way I could get that article to you (bearing in mind we've previously discussed the separation between RL/WL)? Sandbh (talk) 05:11, 13 November 2016 (UTC)

Another look: Groups 2 and 12

I presume that if the authors applied their approach to groups 2 and 12 that they would recommend placing Be and Mg in group 12 since Be Mg Zn Cd and Hg are "so" different from the rest of group 12. Sandbh (talk) 09:04, 9 November 2016 (UTC)

Yes, I was wondering about this too. (I think Hg would also be quite the outlier though, with relativity and the d- and f-block insertions creating a nearly unique set of circumstances on the periodic table that doesn't return till we reach Cn.) It once again boils down to the similarities-vs-trends argument; certainly Be and Mg act more like Zn than Ca, and Sc and Y act more like Lu than La, but we are not looking for something similar to them but for something different from them that visibly continues the trend down. Double sharp (talk) 09:18, 9 November 2016 (UTC)

Earlier discussion

Have you looked at Be-Mg-Ca vs Be-Mg-Zn? I usually cite this as an example similar to Sc-Y-La vs Sc-Y-Lu. In this case, Zn seems a better fit physically, since you cannot exactly use Ca as a structural metal. There are also significant chemical differences between Mg and Ca (look at their behaviour in ammonia solutions). And yet everyone is behind Ca, even though I could argue that Ca, Sr, and Ba show some transition-metal character in that the empty d-orbitals are low enough to contribute to excited states and even sometimes bonding (like how it is often argued that La "really" has f-orbital involvement). Double sharp (talk) 14:34, 3 October 2016 (UTC)

I think the Be-Mg- question is a bit of a side issue that doesn't diminish the contribution of Horowitz and Sârbu's findings to the overall Sc-Y- question.

What I was trying to say here is that if you look at primarily physical properties, Zn is a better fit with Be-Mg- than is the case for Ca. Yet nobody puts Be and Mg over Zn anymore, because Be-Mg-Ca shows simpler chemical trends. As such I find this a weak argument: since chemical properties seem to overrule physical properties in periodic table placement in the case of Be-Mg-Ca, why should it not also be the case for Sc-Y-La? Double sharp (talk) 11:59, 5 October 2016 (UTC)

If chemical properties trump physical then Lu has more in common with Sc and Y than is the case with La, does it not? This is not a trick question, I want to ensure our arguments are consistent, There are the two Cotton arguments, however weak, Nelson's carbonyl argument, the yttrium group argument, and the old separation group argument. Does La have better chemistry-based arguments for fitting under Sc-Y- than Lu? Sandbh (talk) 01:45, 6 October 2016 (UTC)

I think it is rather chemical trends that trump physical ones. Basicity and size usually increase down the table: that's why Be-Mg-Ca is preferred, since Zn is more like Be and Mg than Ca is, even chemically! (Be and Mg are class-b metals like Zn while Ca is class-a.) This is why I think La is better under Y, because instead of being confusingly similar, it continues the trend down group 3 (Sc to Y) of increasing size and reactivity. Double sharp (talk) 03:50, 6 October 2016 (UTC)

Perhaps we should also take a lesson from group 14 (the crystallogens: I love that name). Every adjacent pair of elements is similar, indeed similar enough that Mendeleyev had no problem predicting the properties of Ge based on what he knew about Si and Sn. But if we look at the extreme members of the group, C and Pb, we see that similarities have been swamped by trends. Both may be tetravalent main-group elements, but the recurring theme of increasing metallic character down the group has conquered all. Why should it not do so in its mellowed guise as increasing basicity down group 3, before the contraction of the 4f and 5d orbitals strikes after lanthanum? Double sharp (talk) 04:27, 6 October 2016 (UTC)

Would you once again tell me why the Be-Mg-Ca/Zn alternative (which draws a parallel with Sc-Y-La) is okay to consider but the B-Al-Sc/Ga (which draws a parallel with Sc-Y-Lu) isn't? I didn't understand it the last time.--R8R (talk) 04:56, 6 October 2016 (UTC)

Because Be, Mg, Ca, and Zn all have an s² configuration, so the choice is not clear solely on that basis: we have to look at other properties. On the other hand, while B, Al, and Ga all have s²p, Sc has s²d, so the choice is clear. B-Al-Sc leads to inconsistent electron configurations that show up in broken trends in mp, for instance. Sc-Y-La is more like the former case because Sc, Y, La, and Lu all have an s²d configuration. Double sharp (talk) 05:36, 6 October 2016 (UTC)

Hmmm. I don't like this explanation. While Mendeleev and his contemporaries constructed the periodic table based on chemistry, we now know that the reasons the PT looks the way it does don't stop at chemistry and can be traced further to atomic configurations (which also help define chemistry). As such, we know that zinc has 30 electrons, not two, and that d-block does in fact play a role in period 4 (we even have an article on the topic), but these simplified valence configs don't acknowledge this. That is to say, ns² != ns²(n-1)d¹⁰ just as ns²(n-1)d¹ != ns²np¹. Frankly, I don't see how these two can be viewed as different situations.--R8R (talk) 21:38, 6 October 2016 (UTC)

But is 3d active in Zn? There is not even predicted to be any possibility of d-orbital involvement in the bonding of Zn and Cd; even Hg can only be coaxed to do it under extreme conditions. Just because zinc has 30 electrons doesn't mean all of them are active. Gallium has 31 electrons and has the inner filled 3d shell that aluminium (13 electrons) doesn't, and that makes a bit of difference for physical properties, but not for chemical properties: both have three valence electrons in s²p (whereas scandium is ds²). If we considered core electrons, we couldn't even put F and Cl above Br because the first two are s²p⁵ whereas the last is d¹⁰s²p⁵. But isn't that a bit silly, since 3d is not actually doing much in bromine? I know and understand that the 4f and 3d contractions have an effect in the following block, but these differences are mostly quantitative, rather than the qualitative differences between Sc and Ga. Double sharp (talk) 01:24, 7 October 2016 (UTC)

Depends on what you define as "active." If you stop at just being valence electrons, then the next question would be, "So if the d shell doesn't matter as it doesn't openly participate in chemistry, then why is a lone np electron chemically (since that reasoning is based on chemical activity) openly different than a (n-1)d one?", and I don't know why. (And then I re-read what you wrote and saw you said yourself that they don't differ in that respect.) So it seems that debunking the legitimacy of the group III analogy also debunks the legitimacy of the group II analogy. I believe it was just bad debunking from the start, but I'd want to hear you out on this.

The difference is admittedly stronger the farther you get from the group II/III divide. In group IV, C and Si are certainly quite different from Ti, which now has real TM character. In group I, the filled p-shell of Na and K can't be breached while the filled d-shell of Cu can. Chemically B-Al-Sc, like Be-Mg-Zn, lead to reasonable trends, as reasonable as B-Al-Ga and Be-Mg-Ca. The problem comes when you look at physical properties, when you then see that the d-electron is more localised, resulting in breaks in the trends of mp, bp, and resistivity. Double sharp (talk) 01:57, 8 October 2016 (UTC)

mp, deg C

2	3	12	13
1287			2076
650			660
842	1541	419	29
777	1526	321	156

bp, deg C

2	3	12	13
2469			3927
1090			2470
1484	2836	907	2400
1382	2930	767	2072

Resistivity, 1×10⁻⁸Ohm

2	3	12	13
3.56			a lot
4.39			2.65
3.36	56.2	5.90	13.6
13.2	59.6	7.27	8.0

Let us leave out group I and IV. I know I'm up for detailed approach, but what do they have to do with the current groups II and III? Can this somehow be put to support either version?

It's the exact same thing at play: a p-electron is less tightly held by the nucleus, but the orbital is less diffuse than a d-electron. Group IV is just a little more obvious, but OK, let's look only at groups II and III. I look at your figures and I see that only in the group 3 column are d-electrons doing anything, so they always end up with the highest mp and bp, higher than anything in group 13 (more obviously in mp). (Boron doesn't count, since it's using covalent bonding instead of metallic bonding. Beryllium is likewise an exception because it's so small that even the s-electrons are very tightly held by the nucleus.) Boiling point shows weaker trends, because gallium is a bit like water: the solid arrangement is broken down in the liquid, which has lower interatomic distances, and so it actually contracts on melting. (Indium is also a bit like this, but not to the extent of contracting upon melting.) But it is still there, only with a few hundred degrees instead of a few thousand.

As for group II, I regret to have to say that there is no simple explanation for the variations in mp and bp. (Throws hands up in despair.) But both groups IIA and IIB are using only s-electrons for these, at least. So it is a different situation from that between group IIIA (using a d-electron) and IIIB (using a p-electron), for which you can see much larger differences. Double sharp (talk) 06:47, 9 October 2016 (UTC)

Now, I want to admit that your line of defense seems to change. You first said the 3d electrons didn't define chem in Zn and you're pushing for physical properties. Anyway, I collected all the data for the properties you mentioned. There are many small observations to be made, but I only want to point out one thing: only with resistivity—one of the three properties you've mentioned—I do clearly see your point. As for mp, the analogy between Be-Mg-Ca/Zn and B-Al-Sc/Ga (the original point of this discussion) can be drawn; as for bp, I wouldn't even put it into question.--R8R (talk) 06:04, 9 October 2016 (UTC)

(Here DS was silent for a while trying to think of exactly what was the smoking gun here.)

Essentially, the issue is that the d-electrons are more localised and contribute much more to the metallic bonding in the group IIIA elements compared to the p-electron in the group IIIB elements. (I am using the old IUPAC system to make a point: here "A" groups are all on the left side of the table and "B" groups are all on the right side). You see the exact same thing when comparing group IVA with group IVB. Furthermore, whereas the group IIIB and IVB elements act like main-group elements, losing the p-electrons before the s-electrons (and only the p-electrons are delocalised for Ga, In, and Tl, as well as β-Sn and Pb), the group IIIA and IVA elements act like transition elements, losing the s-electrons before the d-electrons (and they are all delocalised). Double sharp (talk) 16:14, 8 October 2016 (UTC)

But why does it prohibit drawing the B-Al-Sc/Ga analogy? Of course, if you have the idea that the Sc-Y-La is the version, than than a version, then it may seem justifiable to use this an a good reason to diminish the importance of the other analogy. Without any ideas to begin with, I don't think so. I do accept your point re ionization order, though I'd want to know how much energy it takes to get a Sc⁺ ion to have a config of a main-group element and a Ga⁺ ion to have a TM-like config, but I won't look now. Too tired after a night of coding. (I am inclined to believe in what you say re metallic bonding, as it makes sense, but I can't find any figures to directly assess the degree of this difference). Does that all make up for not allowing the B-Al-Sc/Ga analogy? While I can't say "definitely no," as it's a matter of taste anyway, I doubt it has been shown with the information examined by this point. So far, I don't know any difference in chemistry caused by the 21th electron being a d electron and the 31st one being a p one rather than the d-block contraction, and I assume that while this difference should exist to some extent, this extent is small, and we seem to have agreed on that. Then, moving on to the physical properties, the original analogies are evident in two properties of the three mentioned as prohibitive. Atop of this, some non-quantified information has been put, which I would want to quantify and which could be quantified, that prohibits the analogy in question. With all sincerity, I'm not satisfied by this point to say, "Oh yeah, you were right," though I admit you've made some points.--R8R (talk) 06:04, 9 October 2016 (UTC)

According to NIST, Sc⁺ needs 11736.36 cm⁻¹ to become [Ar]4s². Furthermore, [Ar]3d² is still lower in energy, with [Ar]3d¹4s² being of course the ground state.

I'm not entirely sure what a TM-like configuration for Ga⁺ would be. In the ground state it is of course [Ar]3d¹⁰4s². The next higher states are (in cm⁻¹): [Ar]4s¹4p¹ (47367.55); [Ar]4s¹5s¹ (102944.595); [Ar]4p² (107720.716); and [Ar]4s¹4d¹ (126187.61). Double sharp (talk) 06:31, 9 October 2016 (UTC)

Yeah, as I said, it was a long tiring night. My mistake.--R8R (talk) 21:03, 9 October 2016 (UTC)

I'm against using simplified arguments when discussing a subtle question like the main "-La or -Lu" issue. Why are you leaving out all electrons that aren't as openly active but still important in some ways?

"but these differences are mostly quantitative, rather than the qualitative differences between Sc and Ga" -- can't assess this statement. Why are these "quantitative, rather than the qualitative," where lies the difference, and are these terms even important? can we just go straight to the business? To give context to these questions, I will say I try to minimize the number of questions I see in terms of binary alternatives. Bonding is not ionic, but mostly ionic, etc. This helps see some tendencies the may be overlooked by the superficial binary observing. As a historical example, I'll mention that not taking into consideration the reasons beyond valence (as they weren't yet known) made many people think that thallium was an alkali metal.

Ga is quite amphoteric, like Al and In, and also prefers covalent bonding in its compounds (it's not quite fair to include Tl because it wants to be univalent). Sc on the other hand is reasonably basic. Granted it still somewhat hydrolyses water, but only to the extent of Cr or Fe, and that is because +3 is already a high charge for an ion (you have to get to lanthanide-size like Y before you can really handle it and still be basic; even Th can't manage a true +4). Also, Ga has the textbook properties of a PTM (see Sandbh's article) while Sc is physically an excellent TM and is chemically similar to Mg. Double sharp (talk) 01:57, 8 October 2016 (UTC)

I will also note that Sc and Ga are different not only by their last electrons, but also by a full d shell as well, and this adds a lot to the difference between them. Not sure if that contributes to your argument or mine, probably neither, but I can't leave it out for the sake of adequacy of this mini-argument.--R8R (talk) 19:37, 7 October 2016 (UTC)

The effect of Ga having the filled d-shell is covered in the gallium article which I rewrote. But mostly, the effect is just that Ga is a slightly smaller atom than you would think (e.g. its EN is higher than Al's). In many respects, though, Al is more similar to Ga, In, and Tl than it is to Sc, Y, and La (see the group 13 section in post-transition metal). Double sharp (talk) 01:57, 8 October 2016 (UTC)

P.S. If I haven't misunderstood your argument, it also seems to imply that Lu can't be placed under Y because ds² ≠ f¹⁴ds², just as Zn can't be placed under Mg because s² ≠ d¹⁰s². I don't think that's what you meant, so I have probably misunderstood something. Double sharp (talk) 01:30, 7 October 2016 (UTC)

I am not arguing for or against any alternative; as I told you, I don't see the point. I'm just trying to raven your arguments that I find weak.

My idea was and is that these two approaches are equally valid, and it's not fair to put one over the other one.--R8R (talk) 19:37, 7 October 2016 (UTC)

The main issue I find with the other approach is that while it gives the usual conclusion for Be-Mg-Ca, it does not do so for B-Al-Ga, because it privileges number of electrons outside the noble gas core (notwithstanding that 3d is also part of the core) over exactly what orbitals these electrons are. Note that I say this even though it supports my stand, because I don't find it convincing. (Sc: [Ar]3d¹4s²; Y: [Kr]4d¹5s²; La: [Xe]5d¹6s². You can't get much more consistent! All of them have three electrons outside the noble gas core, and two of them are in an s-orbital and one is in a d-orbital of the preceding principal quantum shell.) Double sharp (talk) 15:21, 8 October 2016 (UTC)

Okay, let's put an end to this discussion with me here. I looked to understand the point of the staircase argument and I did; thank you for explaining it. Not that I am convinced, but I'm currently not looking to convince or be convinced; but at least I can now see the argument as valid in its way.--R8R (talk) 21:03, 9 October 2016 (UTC)

Okay; thank you!

One last thing I should link to: the lanthanide and 3d contractions are in fact a general thing about how orbitals without radial nodes, and also affect 1s and 2p as well. Thus it is a geneeral thing you should expect. Double sharp (talk) 04:20, 10 October 2016 (UTC)

2011: Triads ♥

Scerri (2011 p. 135) suggests atomic number triads support Y-Lu-Lr rather than Y-La-Ac.

Analysis
The suggestion is inconsequential since Sc-Y-La form a triad whereas Sc-Y-Lu do not.

2012: Split d block ♥

Scerri (2012) dismisses Sc-Y-La-Ac on the grounds of a symmetry deficit in the 32-column version:

I say "almost entirely" because there does exist a third option, although this can be dismissed on the grounds that it represents a very asymmetrical possibility. As seen in figure 6, the third option requires that the d-block elements should be broken into two very uneven portions consisting of one group, followed by the insertion of the f-block elements and continuing with a block of nine groups that make up the remainder of the d-block elements. Indeed, this form of the periodic table is also sometimes encountered in textbooks and articles, although this fact does not render it any more legitimate.

In a similar vein, Wulsberg (2000) reckons the chemical and electronic properties of La and Lu (and Ac and Lr) are too close to make a call. He cites Jensen's 1982 arguments saying that the "metallurgical" resemblance is much stronger for Lu than La, so has adopted Lu (and by extension, Lr) below Y. More relevantly, he goes on to note that "an important additional advantage is that the periodic table becomes more symmetrical, and it becomes easier to predict electronic configurations." (p. 53)

Analysis
Scerri notes that, "some textbook authors have taken –Lu-Lr up, but the majority seem reluctant." La-Ac is indeed still the most common form although very few authors show it with a split d block. The vast majority use alternative graphical solutions. For example, the Sargent-Welch table shows a single star above the 'a' in La and a double star above the 'c' in Ac, to denote the footnoted lanthanides and actindes.

A desire to keep the d-block intact is all fine and well from the perspective of Platonic symmetry, but there is already an established precedent in breaking the s-block to prioritise chemistry over Platonic symmetry. Scerri (2015, pers. comm.) has questioned the comparability of splitting one single element (He) with separating an entire group from other d-block groups. On the other hand, He over Ne involves moving an s-block element over two intervening blocks, into the p-block whereas Sc-Y-La-Ac at least maintains its d-block identity. Indeed, Hamilton (1965), shows a periodic table extract (groups 1 to 11, plus footnoted Ln and An, showing Ce, Pr…Lu; and Th, Pa…Lw) with a split d block (the gap is between groups 3 and 4) and says that—without any fuss—this is "the periodic table as it is usually presented".

Even Jensen (1986) has commented on the abuse of symmetry considerations in the construction and interpretation of periodic tables in general, and more specifically (2003) on the triumph of Platonic symmetry over the inconvenient facts chemistry with respect to the placement of the coinage metals in pre-electronic periodic tables (pp. 953–954).

Are we here to draw a table to reflect Platonic symmetry? Or are we here to draw a table to reflect chemical properties? We firmly advocate for the latter.

2013: Carbonyls ♥

Nelson (2013) argues that the number of outer electrons possessed by an atom, and the number required for it to achieve an inert gas configuration exhibit an almost exact periodicity. Further, these two numbers correlate almost exactly with the highest conventional valency and the highest carbonyl valency exhibited by an element. For example in iron carbonyl, Fe(CO)₅, the carbonyl valency is taken to be 10 whereas Fe has a highest conventional valency of 6. Now, while Y, La and Lu all have a highest conventional valency of 3, Y and Lu require only 15 electrons to achieve an inert gas configuration whereas La would need 29. On this basis Nelson perfers Y-Lu rather than Y-La.

Analysis
We can see periodicity in carbonyl valencies but the values of the rare earths carbonyl valencies are tentative, incomplete and based on matrix isolation studies. On the Ln Nelson says, "The values…for the Ln and An are tentative. These are based on matrix isolation studies. I have adopted the formulae for the highest carbonyls suggested by workers in the field. Errors in these will not significantly affect the argument."

The issue we see with basing arguments on such unstable species is that many things that can be done that are not representative of the chemistry of the element being considered. We do not think the existence of iridium(IX) is particularly important when countering the generalisation that beyond group 8, the range of oxidation states shrinks. Jensen himself notes that the possible existence of mercury(IV) is just a tiny exception to the far more characteristic main-group chemistry of Zn, Cd, and Hg. Lastly the very existence of last actinides and the transactinides only occurs under very anomalous conditions: we wouldn't change the name "noble gases" even if element 118 (soon to be oganesson) acts like a reactive nonmetal, and already the halogens are often taken to end at iodine instead of the fugitive astatine. So while this might be true, we feel it has no more bearing on the placement of La than HgF₄ does on the classification of group 12.

We further query what happens to the s-block if one takes this approach? We are not aware of s-block carbonyls, but this would seem to suggest that Mg (which needs 6 electrons to achieve the [Ar] configuration) cannot be placed above Ca (which needs 16 to achieve the [Kr] configuration), and that Sr (which needs 16 to get to [Xe]) cannot be placed above Ba (which needs 30 to get to [Rn]).

2014: Lu as a transition metal ♥

Settouti and Aouragi (2014) compare the physical and mechanical properties of Lu with those of Cs, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, and Bi, using mathematical analysis. They conclude that Lu shares many properties and similarities with period six transition metals and, "and can be well described as a transition metal."

Analysis
The authors go too far in saying Lu may well be described as a transition metal. To substantiate this claim they'd have to show that the properties of Lu in question are closer to e.g. Hf than they are to the other heavy lanthanides, and they did not do that. Other references have different observations. Spedding and Beadry (1968, p. 377), wrote, "Since metallic lutetium resembles closely erbium and holmium, except that it melts at a slightly higher temperature and is essentially non-magnetic, the details of producing, purifying and fabricating it are almost identical with those described under Holmium." Leal, Restrepo and Bernal (2012) compared 4,700 binary compounds of 94 elements. Sc and Y ended up in their own cluster; Lu ended up in a cluster with Er, Ho and Gd.

Name matches position ♥

In a comment to an Eric Scerri blog, McCaw (2014) suggests that putting La and Ac in the f block is pleasingly consistent with their names.

Analysis
We consider this argument to be weak and inconclusive. The reason for using convenient trivial names for categories of elements is to describe and simplify the more complex reality that stands before us, and not to dictate that reality.

Placing La and Ac in the f-block visually separates Lu and Lr from the other lanthanides and actinides in the 18-column form, even though their properties are quite similar to those of the late lanthanides. Admittedly the same could be said about placing La and Ac in the d-block since this visually separates them from the other lanthanides and actinides. Still, while Lu and Lr are always shown or regarded as lanthanides this is not the case for La and Ac, which are sometimes not regarded as Ln or An, for example because "lanthanide" literally means "like lanthanum" and thus should not include La, or because La and Ac have empty and chemically inactive 4f and 5f orbitals unlike the rest of the lanthanides and actinides.

In any event we consider that this argument is almost too weak to bother with.

2015: Dimer spectroscopy ♥

Jensen (2015) cites Fang et al. (2000) who, in discussing the spectra of Sc, Y La and Lu X₂ dimers, and those of some other period 6 transition metals, conclude that lutetium is more like the other transition metals and is therefore a better fit under Y than is the case for La.

Analysis
Correct, but the story is incomplete as Fang et al. do not say anything about the spectra of the group 2 or 1 metals.

Relativistic contraction of 6s shell ♥

Jensen further cites Fang et al. who note that the relativistic contraction of the 6s shell falls on the same trend line as that applying to the periodic 6 transition metals Hf to Ir whereas the contraction for La is more consistent with the trend line for Ce to Yb.

Analysis
Correct at face value, but not the full story since Fang et al. do not extend their trend line into the period 6 metals Ba and Cs. Looking up the applicable data tables cited by Fang et al. (Desclaux 1973) shows that La falls on the Ba and Cs trendline.

• Desclaux JP 1973, 'Relativistic Dirac-Fock Expectation Values for Atoms with Z = 1 to 120, Atomic Data and Nuclear Data Tables, vol. 12, pp. 311–406 (370–371), doi:10.1016/0092-640X(73)90020-X

Aluminide dimers ♥

Jensen cites Ouyang et al. (2008) who note that the "AlLa dimer has a different chemical bond compared with its congeners AlSc, AlY and AlLu. This discrepancy raises the question as to whether it would be more suitable to replace La with Lu in the periodic table."

Analysis
Fine, but not the whole story as the authors fail to say anything about Ba and Cs.

The fact that such arguments are raised says much about how close La and Lu are, since to our knowledge no one has ever argued for the splitting of group 16 even as the dioxides range from molecular polar covalent SO₂ through polymeric SeO₂ and TeO₂ to ionic PoO₂. This thus strikes us a dubious argument for placing elements in the periodic table, at least when presented alone: at the most it might be valuable as a "tipping point" argument only.

• Ouyang Y, Wang J, Hou Y, Zhong X, Du Y and Feng Y 2008, 'First principle study of AlX (X=3d, 4d, 5d elements and Lu) dimer', Journal of Chemical Physics,, vol. 128, no. 7, pp. 074305-1–074305-6, doi:10.1063/1.2831506

Heat of vapourization ♥

Jensen refers to "trends in the [heat] of vaporization for the alternative group sequences Sc-Y-La versus Sc-Y-Lu" and goes on to say, "the latter, rather than the former, corresponds most closely to the group tends observed for this property for the other elements in the early part of the d block."

Analysis
Unclear. The values for La (402 kJ/mol) and Lu (415) are quite close and in comparing these to values for other nearby elements we weren't able to discern anything favouring the placement of either La or Lu under Y.

Ionization energy of Lr ♥

Jensen (2015a) discusses, as reported in the 9 April 2015 edition of Nature, the experimental confirmation of the ionization energy (IE) of Lr and the implications of this for the composition of group 3. The latter question dominated all subsequent news stories on the Nature paper. He finds that no conclusions can be drawn on this question.

Analysis
We agree with Jensen.

La-Ac arguments

1970: Comparison of six properties ¶

Trifonov (1970) compares La and Lu across electronic structure; atomic volume, radius, ionisation energy, and density; and basicity. We have numbered Trifonov's arguments, for ease of reference:

[1] Electronically he says Sc (2, 8, 9, 2), Y (2, 8, 18, 9, 2) and Lu (2, 8, 18, 32, 9, 2) each have only two incomplete shells and that this pattern holds true for the rest of the transition metals proper for periods 4 to 6, whereas La (2, 8, 18, 18, 9, 2) has three incomplete shells.
[2] Placing Lu in group 3 also means there is a consistent difference in atomic numbers of 32 between the period 5 and 6 transition metals, whereas this is not the case for La in group 3.
[3] He further notes (c) that, "…in the spectrum of La the configuration levels containing 4f-electrons are extremely deep—already there is a tendency to strengthen the bonds of 4f-electrons" but that "this can hardly serve as a sufficient basis for considering La as the first element of 4f-family."
[4] For atomic volume, radius, ionisation energy and density he says vertical trends going down groups 3 to 7 favour Sc-Y-Lu but that horizontal trends in periods 4 to 6 for groups 1 to 3 favour Sc-Y-La.
[5] On basic character he says that increasing basicity with increasing atomic number is a general principle for the entire periodic system and since Sc-Y-La follows this pattern, whereas Sc-Y-Lu does not, he overall favours La in group 3.

Analysis
1, 2 and 3 are non-arguments. For argument 4, Trifonov overlooks the fact that vertical trends in groups 1 and 2 favour Sc-Y-La. We agree with argument 5, and his overall support for La in group 3.

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The scope of his arguments on vertical and horizontal trends is too narrow and overlooks, for example, anomalous trends in melting points and Young's modulus, if La is placed in group 3, as discussed elsewhere on this page.

And yet the basicity thing (correlating with size) is so important to the structure of the periodic table that it literally appears in every first-year textbook. Double sharp (talk) 03:32, 4 November 2016 (UTC)

Indeed [1] is very silly with all the electron-configuration inconsistencies. For example, Ni (2, 8, 16, 2) has two incomplete shells, as does Pt (2, 8, 18, 32, 17, 1), but Pd only has one (2, 8, 18, 18). Double sharp (talk) 06:13, 12 November 2016 (UTC)

2008: A pair out of place ¶

REFERENCES: Lavelle L 2008, "Lanthanum (La) and Actinium (Ac) should remain in the d-block", Journal of Chemical Education, vol. 85, no. 11, pp. 1482–1483 • Jensen WB 2009, "Misapplying the periodic law", Journal of Chemical Education, vol. 86, no. 10, p. 1186 • Lavelle L 2009, "Response to Misapplying the periodic law", Journal of Chemical Education, vol. 86, no. 10, p. 1187 • Clark RW & White GD 2008, "The flyleaf periodic table", Journal of Chemical Education, vol. 85, no. 4, p. 497.

Lavelle (2008) says that, "the entire modern basis of the periodic table is the grouping of elements by occupied outer orbital type giving rise to the s-block (two outer electrons in an s-orbital and two groups), the p-block (six outer electrons in three p-orbitals and six groups); the d-block (ten outer electrons in five d-orbitals and ten groups), and the f-block (14 outer electrons in seven f-orbitals and 14 groups)." He says that placing Lu and Lr in the d-block, and La and Ac in the f-block leads to a worse outcome than leaving La and Ac in the d-block since this would represent, "the only case where a pair of elements [i.e. La-Ac] is placed such that they are part of block [i.e., the f- block] with no outer electrons in common with that block." He also relies on the fact that several well-known reference books show La and Ac in the d-block. His position is that, "we [should] use well-established forms of the periodic table…and that, "to suggest otherwise may result in a Pandora's box of a never-ending mutltitude of different periodic tables" (Lavelle 2009).

Analysis
We agree with Lavelle's argument about La-Ac being the only example of "a pair out of place", if they were in the f-block, and we also feel that it is strengthened by the total lack of f-orbital involvement in La and Ac in anything other than the most extreme conditions – which we feel justified in ignoring as they would also imply that K, Ca, Rb, Sr, Cs, and Ba would be d-block elements. And we agree Sc-Y-La-Ac is well established in the literature, for what that is worth.

We also suggest that contrary to Jensen's critique, it is not a weakness of Lavelle's argument to allow Th ([Rn]6d²7s²) in the f-block but not Ac ([Rn]6d¹7s²), due to the lack of low-lying 5f orbitals in the latter as opposed to their presence in the former.

2016: Condensed- v gas-phase electron configurations ¶

Whereas gas phase electron configurations of the Ln and An appear to support Sc-Y-Lu-Lr, condensed phase configurations—which are more pertinent to the chemistry of the elements—support Sc-Y-La-Ac.

Gas phase
Jensen has argued for Sc-Y-Lu-Lr on the basis that the ideal electron configurations of the Ln and An are 4fⁿ 6s² or 5fⁿ 7s². When the actual configurations of the Ln and An are compared with their ideal configurations, we see that a Sc-Y-La-Ac layout yields 20 irregularities as against 9 for a Sc-Y-Lu-Lr layout:

TABLE 1: Sc-Y-La-Ac periodic table (light grey shading = match with idealized number of f electrons; dark grey shading = irregularity)

Period 6	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu
Idealized f-electrons	1	2	3	4	5	6	7	8	9	10	11	12	13	14
Actual number	1	3	4	5	6	7	7	9	10	11	12	13	14	14
Period 7	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr
Actual number	0	2	3	4	6	7	7	9	10	11	12	13	14	14

TABLE 2: Sc-Y-Lu-Lr periodic table f-block showing electron configurations

Period 6	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb
Idealized f-electrons	1	2	3	4	5	6	7	8	9	10	11	12	13	14
Actual number	0	1	3	4	5	6	7	7	9	10	11	12	13	14
Period 7	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No
Actual number	0	0	2	3	4	6	7	7	9	10	11	12	13	14

For idealized f-electron numbers in Table 1 see: Newell, S. B. (1977). Chemistry: An Introduction. Boston: Little, Brown and Company, p. 196. For Table 2 see: Brown et al. (2009). Chemistry: The Central Science (11^ed.). Upper Saddle River, New Jersey: Pearson Education, pp. 207, 208–210. In both cases the counts are consistent with an ideal ground state configuration for f-block elements of [Noble gas](n–2)f ^xns² where n = the period number and x = an integer from 1 to 14. See: Rouvray D. H. (2015). "The Surprising Periodic Table: Ten Remarkable Facts". In B. Hargittai & I. Hargittai (eds). Culture of Chemistry: The Best Articles on the Human Side of 20th-Century Chemistry from the Archives of the Chemical Intelligencer. New York: Springer Science+Business Media, pp. 183–193 (190).

Jensen's assertions are based on gas phase electron configurations and we agree with his argument on that basis.

Condensed phase
We agree with Scerri (2015) that solid state electron configurations are more relevant to the chemistry of the elements.

In this regard, the following two tables compare the idealized numbers of f-electrons for period 6 and 7 f-block elements with the actual numbers of f-electrons in their solid states (rather than their gaseous states). There are 6½ irregularities in the first table compared to 21½ in the second, out of a total of 28 elements.

TABLE 3: Sc-Y-La-Ac periodic table f-block showing electron configurations (light grey shading = match with idealized number of f electrons; dark grey shading = irregularity)

Idealized f-electrons	1	2	3	4	5	6	7	8	9	10	11	12	13	14
Period 6	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb	Lu
Actual number	1	2	3	4	5	~7	7	8	9	10	11	12	~14	14
Period 7	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No	Lr
Actual number	~½	~2	~3	~4	~5	6	7	8	9	11	12	13	14	14

TABLE 4: Sc-Y-Lu-Lr periodic table

Idealized f-electrons	1	2	3	4	5	6	7	8	9	10	11	12	13	14
Period 6	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb
Actual number	0	1	2	3	4	5	~7	7	8	9	10	11	12	~14
Period 7	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No
Actual number	0	~½	~2	~3	~4	~5	6	7	8	9	11	12	13	14

The position of each element in the f-block determines its idealized number of f-electrons. For example, in an Sc-Y-La-Ac periodic table, promethium is the fourth f-block element in period 6 and its idealized number of f-electrons is therefore 4.

For the actual numbers of f-electrons in (a) solid lanthanides and (b) solid actinides see: (a) Johansson B. & Rosengren A. (1975). "Interpolation scheme for the cohesive energies for the lanthanides and actinides". Physical Review B. 11 (4), pp. 1367–1373 (1367), doi:10.1103/PhysRevB.11.1367; Greenwood N. N. & Earnshaw A. (2002). Chemistry of the Elements (2nd ed). Oxford: Butterworth-Heinemann, pp. 1232, 1234: "…most of the metals are composed of a lattice of Ln^III ions with a 4fⁿ configuration and 3 electrons in the 5d/6s conduction band. Metallic Eu and Yb, however, are composed predominately of the larger Ln^II ions with 4fⁿ⁺¹ configurations and only 2 electrons in the conduction band." (b) Haire R. G. (2007). "Insights into the bonding and electronic nature of heavy element materials". Journal of Alloys and Compounds. 444–445, pp. 63–71 (65), doi:10.1016/j.jallcom.2007.01.103; Moore K. T. & van der Laan G. (2009). "Nature of the 5f states in actinide metals". Reviews of Modern Physics. 81 (1), 235–298 (269; 270; 272; 275; 276; 283; 286), doi:10.1103/RevModPhys.81.235; Lawson A. C. (2016). "5f-electron localisation in the actinide metals: thorides, actinides and the Mott transition". Philosophical Magazine Letters. 96 (3), pp. 85–89 (87), doi:10.1080/09500839.2016.1157634.

In thorium, the number of f-electrons is shown as a fraction due to a 5f/6d overlap. See: Johansson B., Abuja R., Eriksson O. & Wills J. M. (1995). "Anomalous fcc crystal structure of thorium metal." Physical Review Letters. 75(2), pp. 280–283 (282), doi:10.1103/PhysRevLett.75.280. Some or all f-electrons in the early actinides are itinerant, and become hybridized with ds electrons and orbitals. That, and the rarity and radioactivity of the metals involved, makes it hard to pin down their f-electron numbers beyond approximations (as denoted by ~).

Conclusion
On the basis of solid phase electron configurations we submit that the case for Sc-Y-La-Ac is abundantly clear.

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In the gas phase, the electron configurations of most of the lanthanides is [Xe]4fⁿ⁺¹6s², which seems to correspond better to the Sc-Y-Lu-Lr hypothesis. There are four exceptions. Gd and Lu may be rationalised by invoking the stability of a half- or fully-filled 4f shell, corresponding to the easy reduction of Eu and Yb to the +2 state. Yet La and Ce are a little odd here. If 4f is supposed to, by the Aufbau principle, be lower in energy than 5d, then why is 5d filled preferentially in La, with the [Xe]4f¹6s² configuration only appearing at very high energies? (In the case of Ac, the [Rn]5f¹7s² configuration would be so high in energy that ionisation would actually happen first.) Why is it that, even with the sudden contraction of the 4f orbitals after La, we cannot avoid 5d occupancy in Ce even in the gas phase?

Additionally, chemical arguments also call into question the predictions of a Sc-Y-Lu-Lr table. We know that the 4f subshell is buried deeply in the core due to its low principal quantum number. So why are the lanthanides not predominantly divalent (with the exception of Eu and Yb), losing only the 6s electrons?

To answer these questions, we should look at the condensed-phase electron configurations, since they tend to be more chemically relevant than the gas-phase ones. And lo and behold, we find instead that with just two exceptions, every last one of the lanthanides has a [Xe]4fⁿ5d¹6s². The exceptions? Eu and Yb, because of the stability of a half- or fully-filled 4f shell. This certainly supports a Sc-Y-La-Ac table, in which one column of the d-block is filled at La and Ac, the f-block intervenes starting at Ce and Th, and then the other nine columns of the d-block fill until Hg and Cn. It also supports their chemistry: for if it were really true that their configuration is for the most part [Xe]4fⁿ⁺¹6s², what with 4f drowned into the core, it is difficult to explain the massive preference for trivalence along the lanthanide series.

And what of the actinides? For Ac to Cf, we have exactly the same story. Th and Pa even go overboard with configurations approaching [Rn]6d²7s² and [Rn]5f¹6d²7s², with only minor 5f involvement in both cases. It is only when 5f is drowned deeply into the core near the end of the actinide series, from Es to No, that things change and we obtain the expected [Rn]5fⁿ⁺¹7s² configuration. (Although Lr is expected to have an anomalous p-electron in the gaseous phase, it is predicted to have the expected [Rn]5f¹⁴6d¹7s² configuration in the condensed phase.) And these four elements are exceptional in preferring the divalent state! Only for the late actinides is the divalent state even stable in aqueous solution, let alone the most stable state for nobelium!

Minor digression from copy editing: — Herewith an "elephant stamp of quality" for the above section of the manifesto — Sandbh (talk) 07:35, 12 November 2016 (UTC)

Blocks ¶

We submit that the concept of periodic table blocks supports Sc-Y-La-Ac.

Usually, a block starts when the first electron in that kind of subshell enters and stays, and it ends when it becomes full. After all, an f-block element must have non-hydrogenlike f-orbitals that have been filled for it to deserve the name. Hence the d-block starts at Sc, [Ar]3d¹4s², and ends at Zn, [Ar]3d¹⁰4s². Now, if we start the f-block at Ce and end it at Lu, it starts when the first f-electron enters and ends when the f-shell is full. If we start it at La and end it at Yb, it starts before the f-orbitals become chemically active and stops just before it sinks completely into the core.

It is worth considering the Sc–Zn case similarly. At the end of the block we have Cu, [Ar]3d¹⁰4s¹, with a filled 3d-shell that can still be ionised. The next element is Zn, [Ar]3d¹⁰4s², with a 4s differentiating electron; but it is considered the end of the d-block because this is where the d-shell first becomes chemically inactive. Is this not more similar to Yb and Lu than to Tm and Yb?

Just as 3d only collapses and drops below 4s after Ca and thus the d-block begins at Sc, 4f only collapses and drops below 5d and 6s after La and thus the f-block begins at Ce. (5d had already collapsed after Ba.) The fact that Lu at the end of the f-block cannot use its f-electrons for bonding is immaterial. Neither can Zn at the end of the d-block or Ne at the end of the p-block, reflecting the great stability of a full-shell configuration (not a "pseudo"-full-shell like Cu or Yb where the Aufbau-expected configuration is a low excited state, and thus the shell may be breached). The important thing is that the f-block must correspond to the filling of the f-orbitals with 14 f-electrons and thus it has to have 14 columns. Since it starts at Ce, it must end at Lu.

Jensen's criteria

The preceding viewpoint of block assignment is similar to that promoted by Jensen in Misapplying the Periodic Law:

“ Classification of an element in the periodic table is based on four steps:

1. Assignment to a major block based on the kinds of available valence electrons (i.e., s, p, d, f, etc.).
2. Assignment of the elements within each block to groups based on the total number of available valence electrons.
3. Verification of the validity of the resulting block and group assignments through the establishment of consistent patterns in overall block, group, and period property trends.
4. Verification that the elements are arranged in order of increasing atomic number as required by the periodic law.

”

In the case of the last column of each block, i.e. He, Ne, Ar, Zn, Cd, Hg, Lu, and Lr, we would note that criterion 1 would have to be slightly amended to reflect that some "theoretically available" valence electrons may not actually be ionisable, but we do not think that this seriously affects our argument. To make the block assignment even clearer, we would also add that block assignment is determined by the orbital occupied with the highest angular momentum: thus, for example, an fds² configuration is characteristic of an f-block element.

Jensen claims that criteria 1 and 2 do not lead to an unambiguous assignment in the case of La and Ac, but we find that they actually do. With the understanding that everything said in the following of lanthanum and the following lanthanides is equally true of actinium and the following actinides, La is easily assigned to the d-block because it only has 5d and 6s orbitals available for bonding. Lu, however, has a newly filled 4f shell, similar to Zn with a newly filled 3d shell, that form the last step to fill the d- or f-orbitals. This firmly assigns La to the d-block and Lu to the f-block, which inexorably leads to a Sc-Y-La-Ac table through application of criterion 2. The trends obtained are quite valid, perhaps even more so than for Sc-Y-Lu-Lr, thus fulfilling criterion 3. Finally, criterion 4 implies that the d-block must be split apart to accommodate the placement of La and Ac in group 3. If this does not seem symmetrical, it at least fits the facts of chemistry, in which the d-subshells collapse and become chemically active after group 2, but the f-subshells only do so after group 3.

Superheavy elements: eka-actinium and eka-thorium

A possible wrinkle in this argument for block assignment is that by period 8, relativistic effects are expected to become so large that the overlaps produced from such a strict definition of where blocks start and end would be intolerable, and may not accurately reflect the elements' chemistry: for example, the 8p level is expected to split into an 8p_1/2 level, that begins filling at Z = 121, and an 8p_3/2 level, that does not finish filling until Z = 172. However, it is also prudent to note that past Z = 122 (eka-thorium), no complete and accurate calculations are available, and the chemical interpretation of the properties of the elements past eka-thorium is disputed between authors. Hence, for example, Fricke considered Z = 164 to be a dvi-mercury, while Nefedov considered it to be a dvi-platinum, and Pennemann even predicted that it might show some dvi-radon or dvi-lead properties as well. Even the actual electron configurations of some of these elements are in dispute. Therefore, we submit that this wrinkle is of questionable relevance today.

The only possible exception might be in the cases of eka-actinium and eka-thorium, respectively elements 121 and 122, which have received complete calculations by Ephraim Eliav et al. and thus may be of some relevance here, proceeding with all due caution as predicted properties are obviously not on the same footing as empirically determined properties. While eka-actinium is expected to have [Og]8s²8p¹ as the ground state, the first excited state should be [Og]7d¹8s² at a mere 0.412 eV; thus the 7d, 8s, and 8p orbitals contribute, and 7d is of highest angular momentum and firmly puts eka-actinium in the d-block with scandium, yttrium, lanthanum, and actinium. Similarly to lawrencium, therefore, despite the d-electron being substituted by a p-electron, Lr and E121 are more similar respectively to their lighter congeners Lu and Ac than Tl and Nh with their superficially similar gas-phase electron configurations.

In eka-thorium, the ground state is predicted to be [Og]7d¹8s²8p¹, but low-lying configurations involving the 6f level are predicted for the +1, +2, and +3 cations. The 5g level is instead not yet involved, firmly putting eka-thorium as the beginning of the f-block with cerium and thorium. So, while the beginning of the 5g series remains as yet unexplored, the first four undiscovered elements do not appear to necessitate any revision of the concept of blocks at the moment, instead taking their places quite naturally below Fr, Ra, Ac, and Th. As Scerri has noted, 'This seems to be further testament to the underlying fundamental nature of the periodic law, which continues to stand firm against the threats from quantum mechanics and relativity combined together.' Indeed, if we are permitted a mix of metaphors, out to the furthest reaches yet explored of the Sea of Instability, Mendeleev continues to steer deftly and skilfully between Scylla and Charybdis.

Chemical behaviour ¶

We have repeatedly observed that Sc-Y-La-Ac is a better fit with group 1 and 2 trends, including increasing basicity, whereas choosing Sc-Y-Lu-Lr has been shown several times, including by Jensen, to more closely parallel trends in groups 4 to 10 later in the d-block. Indeed, Laing (2009, p. 12) says a reasonable case could be made for La below Y on the basis of comparing Ca-Sc, and Sr, Y.

We further note that group 3 shows chemical behaviour that is manifestly uncharacteristic of the transition metals proper. Group 3 does not show the complex coordination chemistry that is characteristic of transition metals; they do not show multiple oxidation states; and they are far more reactive and electropositive than any other transition metals, approaching the s-block metals in both properties. Lanthanum in particular is such a hard base that it is taken up by the body as if it were calcium.

On the above bases we contend that the choice of Sc-Y-La-Ac over Sc-Y-Lu-Lr is clear.

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But choosing Sc-Y-La tends to show simple trends of increasing basicity down the table, similar to its neighbours Ca-Sr-Ba, which are much more similar to them chemically than are their other neighbours Ti-Zr-Hf. After all, the +4 state is too high to be ionic in group 4—yes, even for Th and what little we know of Rf. While one can obtain true aquated La³⁺, hydrolysis proceeds so far for Hf that you get HfO²⁺ instead. And so on.

We realise that Sc-Y-La-Ac makes an 32-column table with a broken d-block. But so what? We already have an broken s-block in the table. And are we drawing these rectangles for Platonic symmetry, or are we trying to show the actual chemistry of these elements to the best of our ability? If the latter, the choice seems clear. Besides, as …has pointed out, pure symmetry is only at its most beautiful when it is broken.

Lu-Lr and La-Ac arguments compared

A. It looks like there may be three kinds of Lu-Lr arguments:

1. trend similarity to groups 4–10
2. meaningless commonalities of Lu with Sc and Y; and
3. inconsequential, ephemeral, or baseless (including gas phase configuration) arguments

B. For La-Ac there are:

1. Trifonov's basicity argument, as also noted by Shriver and Atkins
2. Lavelle's pair out of place (surprisingly effective)
3. condensed phase electron configurations
4. the start and end of blocks; and
5. group 3 behaviour as pre-transition elements, including trend similarities as noted by Laing

A1 and B5 cancel out.

That leaves B1–4 as the swing-arguments.

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I think B4 and B2 are rather similar. What both of them essentially boil down to is that La and Ac can't be f-block elements because they have no f-involvement. Double sharp (talk) 08:45, 13 November 2016 (UTC)

Conclusion

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References

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• Matthias BT, Zachariasen WH, Webb GW & Engelhard JJ 1967, 'Melting point anomalies', Physical Review Letters, vol. 18, no. 19, pp. 781–784; Kmetko EA & Hill HH 1976, 'Anomalous melting of f electron metals (with attention to Pu)', Journal of Physics F: Metal Physics, vol. 6, no. 6, pp. 1025–1037
• McCaw C 2014, "Thanks Eric for promoting this point of view...," in Five ideas in chemical education that must die: Part five, posted by E Scerri, http://www.rsc.org/blogs/eic/2015/09/periodic-table-group-3, accessed 12 November 2016
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• —— 2012, 'Mendeleev's Periodic Table Is Finally Completed and What To Do about Group 3?', Chemistry International, vol. 34, no. 4; see also Scerri 2015, 'Five ideas in chemical education that must die - part five', Education in Chemistry blog
• Settouti N & Aouragi H 2014, 'A Study of the Physical and Mechanical Properties of Lutetium Compared with Those of Transition Metals: A Data Mining Approach', JOM, vol. 67. no. 1, pp. 87–93, doi:10.1007/s11837-014-1247-x
• Smith JL 1980, 'Superconductivity in the Actinides', in Superconductivity in d- and f-band metals, H Suhl and MB Maple (eds), Academic Press, New York
• Spedding FH & Beadry BJ 1968, "Lutetium", in CA Hampel (ed.), The encyclopedia of the chemical elements, Reinhold Book Corporation, New York, pp. 374–378
• Trifonov DN 1970, Rare-earth elements and their position in the periodic system, translated from the 1966 Russian edition, Academy of Sciences of the USSR Institute of the History of Natural Sciences and Technology, Moscow, published for the Atomic Energy Commission and the National Science Foundation, Washington, by the Indian National Scientific Documentation Centre
• Wulfsberg G 2000, Inorganic Chemistry, University Science Books, Sausalito, CA
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Left overs for now

Do we know what the condensed phase electron confg of La is? If I recall this is not known for sure yet? I'd see if I could find this again myself but am sarch constrained right now. Sandbh (talk) 01:02, 6 October 2016 (UTC)

Since 4f involvement for La is debated, it must be predominantly 5d¹6s² like the others: where else would the third electron go? The fact that the cohesive energy follows the trend line from Sc to Y supports this, since Al (with p instead of d) does not fall on this line and an fs² lanthanum also would not (there are differences in the cohesive effects of the p, d, and f electrons). It is not unusual for condensed-phase configurations to be a bit fuzzy: that of Ni is infamously so, with an about equal mix of 3d⁸4s², 3d⁹4s¹, and 3d¹⁰. But for 4f involvement in La to still be undetectable, even when many would be looking for it, strongly suggests to me that if it is involved at all, it is not so to any important degree. Double sharp (talk) 03:56, 6 October 2016 (UTC)

I was under the impression that we sorted it out already with the other lanthanides as [Xe]5d¹6s²? Double sharp (talk) 03:40, 5 November 2016 (UTC)

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@R8R Gtrs: Could you look up this reference(?): Shemyakin FM, Zh. Obschch. Kim., 2, 62 (1932). Chistyakov mentions this source as one consideration which requires -Y-Lu rather than -Y-La, but does not clearly elaborate. It may be something to do with atomic spectra judging by some of the other references he cites, but as he doesn't list the article title there's no way of knowing without checking it out. Thank you. Sandbh (talk) 01:51, 15 December 2015 (UTC)

I looked it up some time ago; see my re under point 2. The article is titled, "To the question of including the rare earths"; here's a photo of the table described in the article: http://s4.postimg.org/n22tahdbx/image.jpg --R8R (talk) 19:10, 15 December 2015 (UTC)

Picture is great. I see that he lists what we call group 3 as Sc-Y-Lu-Ac and that he then lists La to Eu and Gd to Yb as two separate but parallel group 3 subgroups. Pretty good effort for 1932, particularly for an 8-column table. Sandbh (talk) 10:10, 16 December 2015 (UTC)

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Allen electronegativity is perhaps not the best choice here since Wikipedia's definition makes it unclear how it would work outside the s- and p-blocks.

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Postscript: From Russell & Megger (1932, p. 625): "All the available data (wave-length measurements and intensity estimates, temperature classes, Zeeman effects) on the lanthanum lines have been correlated and interpreted in an analysis of the successive optical spectra. The total number of lines classified is 540 in the La I spectrum, 728 in the La II spectrum, and 10 on the La III spectrum.

Series-forming terms have been identified in each spectrum and from these the ionization potentials of 5.59 volts for neutral La atoms, 11.38 volts for La⁺ atoms and 19.1 volts for La⁺⁺ have been deduced.

Lanthanum is a chemical analogue of scandium and yttrium but, although the corresponding spectra are strikingly similar, some interesting differences are noted...the... s²d configuration describes the normal state of the neutral atoms in each case...In addition, the first two spectra of La exhibit a large number of (odd) middle-set terms ascribed to the binding of an f electron."

• Russell HN & Megger WF 1932, An analysis of lanthanum spectra (La I, La II, La III), Bureau of Standards, Journal of Research, vol. 9, no. 5, pp. 625--668

Sandbh (talk) 21:27, 14 December 2015 (UTC)

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This actually makes an interesting analogy between the d- and f-blocks in the Sc-Y-La version. If you look at 3d, Cu is [Ar]3d¹⁰4s¹, with the complete d-subshell in the ground state, but which nevertheless can be breached easily in Cu²⁺, [Ar]3d⁹. Then we follow it with Zn, [Ar]3d¹⁰4s², where the d-subshell can no longer be breached: the highest oxidation state is Zn²⁺, [Ar]3d¹⁰. In the next row, 4d is more stabilised, and so neither Ag or Cd is particularly happy to breach the d-subshell, although Ag can be forced to form Ag²⁺ when strong oxidising agents like F₂ are around.

Now if you look at 4f, Yb is [Xe]4f¹⁴6s², with the complete f-subshell in the ground state, but which nevertheless can be breached easily in Yb³⁺, [Xe]4f¹³. Then we follow it with Lu, [Xe]4f¹⁴5d¹6s², where the f-subshell can no longer be breached: the highest oxidation state is Lu³⁺, [Xe]4f¹⁴. In the next row, 5f is even more stabilised near the end, and so nether No nor Lr is particularly happy to breach the f-subshell, although No can be forced to form No³⁺ when strong oxidising agents like Ce⁴⁺ are around.

Furthermore, we think there are good grounds for considering [Xe]4fⁿ6s², which is Jensen's preferred idealised ground state for the f block elements, to be an anomalous configuration.

In the metallic state, the electron configuration of all but two of fourteen lanthanides from La to Lu is undeniably [Xe]4fⁿ5d¹6s² (n = 0–14), as you would expect from their trivalence. The exceptions are the divalent Eu and Yb, which are stabilised by the half- or fully-filled 4f subshell, just like Cr and Cu are often said to be. (After all, Scerri has explicitly advocated using condensed-phase electron configurations, not gas-phase ones, since the former are more relevant to chemistry.) We also know that the first subshell of a given angular momentum is usually odd in behaviour.

But if you look at 5f, which penetrates less into the nucleus and participates more (at least, in the first half of the series; in the second half relativistic effects help strengthen the opposite trend), we get more of those configurations. Th is anomalous no matter how you look at it, but Ac, Pa, U, Np, Cm, and perhaps Bk show the configuration with 6d in the gas phase, while Pu, Am, Cf, Es, Fm, Md, No, Lr show the one without 6d. Furthermore, 6d is contributing in the metallic bonding in all the actinides from Ac to Cf in the condensed phase. You may get more than one 6d electron, but it's a bit difficult to speak of exact configurations at such high atomic number (there was, as recently as 2006, still a bit of a dispute on whether Pa was 5f¹6d² or 5f²6d¹); the main point is that 6d is involved in the early actinides like 5d was in the lanthanides.

Now we count: out of the 30 lanthanides and actinides, 23 of them have a d-electron in their condensed-phase configuration against 7 which don't (Eu, Yb, Es, Fm, Md, No, Lr).

Now which is anomalous? It's certainly more convincing and lopsided than the 16-14 split in 3d–5d based on Scerri's table (count either La or Lu – it doesn't matter, neither is anomalous). We think it's convincing evidence that when it comes to chemistry, we really do to a first approximation have one column of the d-block filled, the rest of the f-block intervening, and then the other nine columns of the d-block.

@Double sharp: You seem to be mixing gas phase and condensed phase arguments in the last four or five paragraphs. Could you have a look at this and ce as required? Sandbh (talk) 04:15, 5 November 2016 (UTC)

Yes, I think I was still organising my thoughts when I wrote that. I think the La manifesto has a better version of this, in "Condensed-phase electron configurations" and "Blocks". Double sharp (talk) 04:19, 5 November 2016 (UTC)

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Actually, I think introducing the word "graphically" is the problem. One can not reason: 'that's a unique graphic thing in the PT, so that "unlikelyness" is an argument against it'. Obviously, the He positioning is another break of pattern example. If one concludes that group 3 is Sc-Y-La-Ac (or that this is a well-based variant, given the criteria applied), then this ends up with a split d block, full stop. Unless you want to break the rule of ascending atomic numbers in the PT.

What we want to show is for the sources, how we show it is just an editorial choice. As we are free to pick out background category colors. And the graph is just a how thing. Now those many authors who show La-Ac with footnote-placeholders in the very same element cell are just sloppy or bad graphicists. Their PT does not show what they state. (For example, here is another(!) IUPAC PT that 'says' there are 32 elements in group 3). I am not worrying about the IUPAC, they'll learn to be consistent in the end. But I am worried about fellow-editors here who keep creating arguments from a proven misformed PT. It is simple: we reject each and every PT presentation that has, clearly or by suggestion, by graphical intention or bad form, 30 (or 32) elements in group 3 N. -DePiep (talk) 15:51, 16 December 2015 (UTC)

• 1. re Sandbh: "Scerri supports –Lu-Lr on the grounds that, essentially, -La-Ac results in a split d-block". This is a stronger conclusion that Scerri makes. He just calls it "a very asymmetrical possibility" to split the d block, and nothing more. So (how strange it is to foul Scerri for this), this is not enough a source to dismiss one option. It would refute all previous 18 more thorough (and non-graphical!) sources.

And from your 2nd ink, Scerri again:

For me, this [increasing atomic numbers] is a virtually conclusive argument in favour of group 3 consisting of Sc, Y, Lu and Lr. The only fly in the ointment is a third possibility, but this involves an awkward sub-division of the d-block elements (Figure 3). As such, it is not a fatal objection to the group 3 assignment that is being proposed in this article.

So nothing 'essentially' or 'grouds' in a split d block'.

• 2. re "Sargent-Welch" PTs you introduce(!): [1] (images) shows they all have 32 elements in group 3. To be binned. Zooming out: Sandbh, why do you keep pushing & abusing the Sc/Y/*/** form? Some times, like here, even trying to construct a source-argument from that graph? Thought we (Scerri and I ;-) ) had mentioned the arguments. -DePiep (talk) 16:29, 16 December 2015 (UTC)

The word "graphically" is the answer. Even as helium or even hydrogen float away, they still remain s block members, just for obvious reasons very different than the others. Splitting the d block means there is a d block group, then 14 f block columns, and then the d block again. Nothing like that is present in the PT elsewhere. (As I argued above, this does not unquestionably state the d block just can't be split, but this does reduce the likeliness of such a split if we assume we don't actually know the correct answer.)--R8R (talk) 09:06, 30 November 2015 (UTC)

Perspectives on symmetry Here (in parts).

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I agree Ln don't form stable carbonyls, hence the reference to matrix isolation studies, but I don't think the instability of these compounds affects the merits of his argument, which is about carbonyl valency periodicity rather than stability.

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MacKay et al. are plausible but not definitive. The only implication I can draw from Zhang et al is that the lanthanum ion (La³⁺?) uses its empty f orbitals in coordination bonding (as suggested by MacKay et al., and consistent with Nelson in #25) but why it would do this in the substance being studied (B and La co-doped TiO₂) isn't clear to me.

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Trifonov appears to discount his 2½ electronic arguments in favour of his single basicity argument. The latter argument is flawed since basicity does not always increase with increasing atomic number.

Sc and Lu chemistry

The (developing chemistry) of scandium is that of a slightly smaller version of lutetium. (according to Cotton)

I presume this is a quote from this paper. Yet Sc is still different because of the size. Lu might form 8-coordinate aqua ions (while La is happy with 9-coordination), but Sc is smaller still and forms 7-coordinate aqua ions. There are also differences in complex chemistry. For instance, Sc(NO₃)₃ does not bind directly to crown ethers, but M(NO₃)₃ (M = Y, La, Ln) do. Again, the size is a little too small for it to work the same way like Y does. It's worth noting that Cotton also said that the resemblance is incomplete, IIRC. Besides, I think "similarity in size" is a worse criterion than "size generally increases significantly down the table", as that is a more general trend. (Otherwise, why don't we put Be and Mg over Zn?) Double sharp (talk) 14:34, 3 October 2016 (UTC)

Yes, that's the right quote. I don't think size is the main consideration. I only quoted this one because Cotton chose to compare the developing chemistry of Sc with that of Lu, rather than Sc.

Similarity of chemistry may not indicate anything more than similar size and valency, though. Consider Ti, Zr, Hf, and Th: the last of these is not quite like the others despite its very similar chemistry, being an f-block element (despite having a 6d²7s² configuration, the Th³⁺ ion quite clearly shows 5f involvement by being 5f¹, though the metal does not show much if any at all). And the small size of Ti makes it act differently from the other three as well. So now we have Th similar to Zr and Hf but in a different group, and Ti not so similar but in the same group. Therefore, we must admit the possibility that this is so with La and Lu with reference to Sc and Y as well. Double sharp (talk)

In general, I like observing this argument from distance and not intervening, but this argument touched me. Its value is, I think, less than zero: it renders the whole argument useless. Indeed: if such dissimilarities are within the normal range, then how can you even expect this argument to ever result in a conclusive outcome, as it must work both ways? Then I would expect you to supplement this statement with amendments to make the -La-Ac option look good (maybe I'm overthinking this, but that's the impression I got), but why not do it in first place? Period 4 differing from periods 5 and 6 is an absolutely different issue than the uncertainty in period 6, as the two are caused by different reasons, and the Zr-Hf-Th similarity is different from both of these, and it only works in a way because element 104 is for some reason not considered (imagine we excluded either La or Lu from this argument and tried to prove the other one fits: that would be a very incomplete "proof"), which is expected to be much closer to the rest of group 4 than thorium.--R8R (talk) 04:56, 6 October 2016 (UTC)

I didn't look at Rf because it's not known well enough, but what we do know indicates that it is also different. The point I am trying to make here is that similarity in chemistry (e.g Y-Lu, Zr-Hf, but more oddly Fe^III-Ga^III, Be-Al and Mg-Zn) is very much a function of size. Not all these pairs are even in the same group. Yet we put C and Pb in the same group despite their profound differences because they share something more than superficial similarities. You can talk about a trend from C to Pb where each element is more metallic than the previous one. Likewise you can talk about a trend from Sc to Ac where each element is more electropositive than the previous one. And that, I think, trumps superficial similarities. Double sharp (talk) 05:36, 6 October 2016 (UTC)

I see this as differing from what I originally responded to; be that truth or not, "size may look like more than it's worth" is a valid argument.--R8R (talk) 21:38, 6 October 2016 (UTC)

Indeed it is a valid argument, but my main point is that it seems to go against the guiding principle of the rest of the PT (increasing basicity as you go down a group) that leads to Be and Mg being placed over the heavy alkaline earth metals, instead of the more similar and also divalent Zn. So I am also citing precedents for Sc-Y-La by looking at how the rest of the table is organised, including telling decisions for those elements that are difficult to place. Double sharp (talk) 15:23, 8 October 2016 (UTC)

Sc organometallic chemistry

Is generally similar to that of the later lanthanides. (according to Cotton))

Yet there are also similarities to those of Ti–Co, e.g. 3-coordinate Sc[N(SiMe₃)₂]₃. I agree that it is a little large for a transition metal but it is also a little too small to really be "one of the lanthanides" like yttrium is. Double sharp (talk) 14:34, 3 October 2016 (UTC)

I think we agree on this one. Any similarities to Ti-Co, however, aren't germane to what I was attempting to demonstrate, which was the greater similarity that Lu has to Y, than is the case for La and Y.

Certainly Y is the right size to act like a lanthanide, but Sc is far smaller than any of La–Lu. The point I was trying to make is that Sc sits uncomfortably with La–Lu (too big) just as it does with Ti–Co (too small), and is ambiguously poised between the lanthanide and 3d-transition-metal trends. So while I would say that yttrium is very similar to the later lanthanides, I would hesitate to say it for scandium. It doesn't even occur in the same minerals as yttrium, lanthanum, and the rest of the lanthanides! Double sharp (talk) 11:59, 5 October 2016 (UTC)

Early period 5 and 6 transition metals

Show close similarities in properties, in contrast to their period 4 congeners.

Mostly because of the lanthanide contraction. And if we are talking about that, the contraction of the 4f orbitals into the core happens after lanthanum. As well, it is not entirely sure that we should call group 3 transition metals: Cotton certainly doesn't, noting that "they resemble the group 2 elements in reactivity" (which is one of my points). If they are not transition metals, then this is a weak argument. Double sharp (talk) 14:34, 3 October 2016 (UTC)

I need to take a rain check on this one.

My main argument here is that since the contraction of the 4f orbitals into the core only happens after La, the lanthanide contraction must begin after La (just like how, in my other arguments, I have been saying that the f-block begins at Ce and ends at Lu). Hence it makes no sense to say that group 3 must follow the group 4–8 trends, because the f-block insertion happens after the former but before the latter. We do not expect the trends in group 2 to look like those in group 13 because the d-block insertion happens after the former but before the latter. Double sharp (talk) 03:35, 4 November 2016 (UTC)

Periodic law

Applies to physical properties as well as chemical properties

Triads

Only as a bonus, Sc-Y-Lu forms a triad whereas Sc-Y-La doesn't.

See my (1) ^_^. Also, despite me thinking this is a weak argument, Sc-Y-La does form an atomic number triad: 39 is in fact the average of 21 and 57. Double sharp (talk) 14:34, 3 October 2016 (UTC)

P.S. Stephen Liddle seems to consider Sc and Y to be f-block elements, effectively privileging chemistry over electron configuration! (Similarly, the periodic table at the back of Clayden's Organic Chemistry, while being Sc-Y-Lu-Lr, floats H and He and colours them as apart from any block; I imagine the motivation is the same.) Double sharp (talk) 14:49, 3 October 2016 (UTC)

Overview of Jensen's arguments

In many cases the Jensen arguments are lame. Some of them are disputed (4f involvement in La is highly suspect), some have been superseded by newer data (both La and Lu are superconducting at low temperatures), and even the chemical arguments stemming from the differences between Y and La (which aren't present for Lu) are simply a result of the larger size of La³⁺ as compared to Y³⁺.

Noted. I will, however, add that the larger size of La³⁺ as compared to Y³⁺ is a big part of the deal to favor the -Lu-Lr config, as I see it, and it's incorrect to just ignore it as if it was nothing. (I never really saw strength in the superconductivity argument anyway.)

I agree that it isn't nothing. I think we just disagree on whether that is important for placing an element in the periodic table. I would tend to note that if you look at the crystal structures of MX₂ (M = Be, Mg, Ca, Sr, Ba; X = F, Cl, Br, I), you will not find a single alkaline earth metal or halogen that leads to a uniform set of structures. The reason, of course, is increasing size down the groups: thus the coordination number of M increases from 4 (Be) through 6 (Mg) and finally to 8 (Ca, Sr, Ba); and as X goes down the group, the trend moves away from three-dimensional structures like fluorite, with BeX₂ (X = Cl, Br, I) forming chains and the others forming layer-lattice structures. But despite this structural potpourri where the twenty alkaline earth halides form ten different structures, no one doubts that groups 2 and 17 still form nice, happy families. I would conclude from this that increasing size down the group is absolutely normal and it cannot really be used to exclude a placement. Double sharp (talk) 04:38, 2 November 2016 (UTC)

But most damningly of all, I could use the exact same arguments to "prove" that Be and Mg do not belong in the same group as Ca and should be moved to above Zn. For instance, Ca dissolves in liquid ammonia but Be, Mg, and Zn will not; Ca metal is fcc while Be, Mg, and Zn are hcp; the mp and bp trends show a discontinuous jump from Mg to Ca but decrease smoothly from Mg to Zn; Ca has low-lying empty d-orbitals that can be used for bonding while Be, Mg, and Zn do not; CaX₂ and MgX₂ for X = F, Cl, Br do not share the same structure; Be and Mg have a rich organometallic chemistry like Zn while Ca does not. Yet no one would agree with that today. If I can use such arguments to "prove" that Be and Mg belong in group IIB instead of group IIA, but you wouldn't be convinced by it, I don't see why they should be any more convincing when applied to proving that Lu and not La belongs in group IIIA. Double sharp (talk) 01:51, 31 October 2016 (UTC)

What this says to me is, "analogies are not necessarily correct." This implies both what you just said and, for example, electronic configs of lanthanides (by the way, La and Ac not fitting in line are not too surprising, and neither are Lu and Lr, so that adds little to discussion, if I am correct). You're actually hinting directly into into why I still like -Lu-Lr better: I think the general principles should allow square blocks and stuff, and the -La-Ac is a customization of the general principle (in one sense). But it's up to people to decide if they want to use that customization, so I can't really have myself arguing for my position, including myself.--R8R (talk) 20:32, 31 October 2016 (UTC)

Regarding electron configurations of lanthanides, when it comes down to it, what pushes me most of all to -La-Ac is that La and Ac do not have any f-involvement at all. If you look at Schwarz's paper on the Aufbau problem (the doi is 10.1021/ed8001286), you will find that, while trends for the energies of the s-orbitals tend to be quite smooth, the d-orbitals tend to suddenly collapse and "fall off the cliff" on the graph only when they start being filled: the same is true for the f-orbitals. He writes, "In the series of elements, (n − 1)d collapses below ns only after group 2, and (n − 2)f only after group 3." Thus 4f is inactive in La just like 3d is inactive in Ca, and the f-block must therefore start at Ce and end at Lu.⁽¹⁾ The trends can easily argue for either way and I agree that the electron configurations of Ce–Yb can support either point. However, I find it completely antithetical to the point of delineating an f-block if it includes elements like La and Ac with no f-involvement at all. This to me completely excludes the possibility of putting La and Ac in anywhere but the d-block. (Lu and Lr are fine in the f-block to me, even though the 4f/5f shell has become full and chemically inactive, because the same is true of Zn, Cd, and Hg at the end of the d-block or Ne and Ar at the end of the p-block. They also form the last step from Yb and No to the completion of the f-subshell, just like Zn completes the d-subshell from Cu.)

I think I've seen Jensen say the opposite: lanthanum does have some freshly discovered f character. Do you happen to remember that? Did it convince you (I think I vaguely remember so did back when you liked -Lu-Lr better)?--R8R (talk) 16:59, 1 November 2016 (UTC)

It did convince me then, but there are two reasons why it doesn't convince me now. The first reason is that it was never a very sure thing. You can get the correct structures of La and Ac if you completely ignore f-orbital involvement, but not for Ce and Th (even though Th is still d²s² in the gas phase). The second reason is that I do not think La showing f-character in excited states is a big deal. Ca, Sr, and Ba show d-character in excited states too, and their d-bands are low enough in energy that they actually are pretty close to the Fermi level and thus contribute. In fact, CaF₂ in the gas-phase is substantially bent and the hybridisation has been shown to be sd (Greenwood and Earnshaw, p. 117): the same is true of SrF₂, SrCl₂, and all four barium dihalides. Yet we don't call Ca, Sr, and Ba d-block elements. Since the de facto position on placing elements is to look at what is occupied in the ground state (yes, that includes 5f for Th), then just as Ca, Sr, and Ba are s-block elements from their s² valence configuration (they finished filling the s-subshell), La and Ac ought to be d-block elements. Supervalent hybridisation is cool but we already have a precedent of not allowing it to influence periodic table placement, since it's not actually a thing that happens at standard conditions. Double sharp (talk) 04:29, 2 November 2016 (UTC)

⁽¹⁾ I do not think he could possibly have meant "group 3" as meaning Sc-Y-Lu, because it is known that the energy-level order in the lanthanides is 5p << 4f < 5d < 6s < 6p, which implies that 4f must have fallen below 6s before the lanthanides started. He can only have meant, therefore, a table where group 3 occurs before the lanthanides start, i.e. Sc-Y-La. This agrees with the quantitative data from NIST in which Ac never shows the [Rn]5f¹7s² configuration. Double sharp (talk) 07:14, 1 November 2016 (UTC)

Other than the question above, very interesting. I certainly find it great that you're begun to dig so deep into this now that IUPAC is working on this. I am not willing to give up my take on this, and I think everyone is free to make their choice. Now that there's a big decision coming, however, it'd be great to include as many relevant factors into consideration as possible into making that decision, and I'm glad you're taking part and digging into details as it seems important to you. I've admired this stance in Sandbh for a long time and I'm beginning to admire that in you.--R8R (talk) 16:59, 1 November 2016 (UTC)

Thank you! It means a lot to me that you think my detail-digging is approaching his level. ^_^ Double sharp (talk) 04:31, 2 November 2016 (UTC)

Lavelle

I think the counter-argument—drawing partly from Jensen (2009)—would be: (1) the modern periodic table is based on idealized electronic configurations rather than actual configurations "and in this fashion functions in chemistry much as the ideal gas law or the concept of ideal crystals and ideal solutions" (Jensen 2009); (2) there are many exceptions to idealized electronic configurations; (3) an 18-column table with Sc-Y-Lu-Lr is closer overall to a periodic table based on idealized configurations than is the case with Sc-Y-La-Ac. [Check me on this. If you say that the f-block starts with Ce-Th then all 28 of the f-block elements are out by one space from their idealized electron configurations. I just had a look at three textbooks with Sc-Y-La-Ac or Sc-Y-*-** and it is a bit of a sorry story to see how they depict their f-blocks. According to one there are 30 f-block elements; a second shows group 3 as Sc-Y-La-Ac but their 32-column table showing the relationship between orbital filling and the periodic table has group 3 as Sc-Y-Lu-Lr, with Lu and Lr coloured as f-block elements, and La-Ac as d-block elements at the the start of the f-block; the third has the blocks coloured right but if you try and compare the f-electron filling sequence in the footnoted Ce-Lu series with the number of f-electons you'll see it's largely out of sync: Ce +1 f¹; Pr +2 f³; Nd +3 f⁴; Pm +4 f⁵; Sm +5 f⁶; Eu +6 f⁷; Gd +7 f⁷; Tb +8 f⁹; Dy +9 f¹⁰; Ho +10 f¹¹; Er +11 f¹²; Tm +12 f¹³; Yb +13 f¹⁴; Lu +14 f¹⁴. Whereas if you start the f filling sequence at La, you get the right synchronization, with only a few irregularities].

Now, since the Sc-Y-Lu-Lr table was identified by Clark and White (2008) as one of the three common forms of 18-column table, in addition to Sc-Y-La-Ac and Sc-Y-*-**, and since a Sc-Y-Lu-Lr periodic table is closer, overall, to the idealized electron configuration periodic table upon which the actual periodic table is based, it follows that this is the "better" (more scientific?) form. Sandbh (talk) 12:15, 17 December 2015 (UTC)

Postscript: Clark and White (2008, above) pooled their general chemistry text collections to survey trends in flyleaf periodic tables from 1948 to 2008. From 35 texts they found 9 × Sc-Y-*-**; 9 × Sc-Y-Lu-Lr and 11 × Sc-Y-La-Ac. Over the last 20 years of their survey period the count was 2 × Sc-Y-*-**; 6 × Sc-Y-Lu-Lr and 6 × Sc-Y-La-Ac. Sandbh (talk) 21:45, 17 December 2015 (UTC)

Further to my above observation about idealized electron configurations, it can be seen from tables 1 and 2 hereunder that 20 of 28 f-block electron configurations in a Sc-Y-Lu-Lr table match the idealized electron configurations underlying the modern periodic table whereas this is the case for only 9 of 28 f-block elements in a Sc-Y-La-Ac table, a disparity of over 2:1 Sandbh (talk) 02:12, 19 December 2015 (UTC)

TABLE 1: Sc-Y-Lu-Lr periodic table f-block showing electron configurations (light grey shading = match with idealized configuration; dark grey shading = irregularity)

Period 6

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Idealized no. of f-electrons

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Actual configuration

5d16s2

4f15d16s2

4f36s2

4f46s2

4f56s2

4f66s2

4f76s2

4f75d16s2

4f96s2

4f106s2

4f116s2

4f126s2

4f136s2

4f146s2

Period 7

Ac

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Idealized no. of f-electrons

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Actual configuration

6d17s2

6d27s2

5f26d17s2

5f36d17s2

5f46d17s2

5f67s2

5f77s2

5f76d17s2

5f97s2

5f107s2

5f11s72

5f127s2

5f137s2

5f147s2

TABLE 2: Sc-Y-La-Ac periodic table f-block showing electron configurations (light grey shading = match with idealized configuration; dark grey shading = irregularity)

Period 6

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Idealized no. of f-electrons

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Actual configuration

4f15d16s2

4f36s2

4f46s2

4f56s2

4f66s2

4f76s2

4f75d16s2

4f96s2

4f106s2

4f116s2

4f126s2

4f136s2

4f146s2

4f145d16s2

Period 7

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Lr

Idealized no. of f-electrons

1

2

3

4

5

6

7

8

9

10

11

12

13

14

Actual configuration

6d27s2

5f26d17s2

5f36d17s2

5f46d17s2

5f67s2

5f77s2

5f76d17s2

5f97s2

5f107s2

5f11s72

5f127s2

5f137s2

5f147s2

5f147s27p1

Trends

Notice that I do not go into a Jensen-like comparison of trends. This is mostly because you can select them at will to prove nearly anything you want (ever wondered why his original paper sums only the first two IEs of the elements in question, instead of the more chemically relevant first three?).

Let's look at his trends. Some of them are disputed (4f involvement in La is highly suspect), some have been superseded by newer data (both La and Lu are superconducting at low temperatures), and even the chemical arguments stemming from the differences between Y and La (which aren't present for Lu) are simply a result of the larger size of La³⁺ as compared to Y³⁺.

But most damningly of all, I could use the exact same arguments to "prove" that Be and Mg do not belong in the same group as Ca and should be moved to above Zn. For instance, Ca dissolves in liquid ammonia but Be, Mg, and Zn will not; Ca metal is fcc while Be, Mg, and Zn are hcp; the mp and bp trends show a discontinuous jump from Mg to Ca but decrease smoothly from Mg to Zn; Ca has low-lying empty d-orbitals that can be used for bonding while Be, Mg, and Zn do not; CaX₂ and MgX₂ for X = F, Cl, Br do not share the same structure; Be and Mg have a rich organometallic chemistry like Zn while Ca does not. Yet no one would agree with that today. If I can use such arguments to "prove" that Be and Mg belong in group IIB instead of group IIA, but no one would be convinced by it, I don't see why they should be any more convincing when applied to proving that Lu and not La belongs in group IIIA.

Since this is a critique of the central point behind Jensen's paper, shouldn't it be nearer the top? Double sharp (talk) 11:33, 5 November 2016 (UTC)

Quite likely, yes. At the moment I've listed our arguments in (more or less) chronological order as we posted them to Wikipedia, so that we can more readily trace the development of our own thinking. Sandbh (talk) 21:24, 5 November 2016 (UTC)

Triads

This argument is frankly beneath consideration. Triads seem to argue for H being placed over F as a halogen, when it absolutely does not fit the trends of that group. Hydrogen is not a strong oxidising agent and in fact is unable to form ionic hydrides with the vast majority of metals. The main shared property is that it forms diatomic molecules at STP, but the alkali metals do so too as gases. Hydrogen's chemistry as H⁺ is also far more important than that of H• (an unstable free radical that doesn't want to exist at STP) or that of the squishy and deformable H⁻ ion. When placed in group 1, hydrogen fits nicely as the least reactive member of the group (doesn't react with O₂ or N₂, or H₂O, and is only coaxed to do so by the halogens). Its proclivity for covalent bonding is easily explained by the fact that H⁺ would be a very small charge and that its formation is unfavourable, thus forming part of a "zeroth-row anomaly". Given that a Li-like model of chemistry is a better predictor of how H actually behaves than an F-like model, I think the concept of atomic number triads needs serious questioning if it recommends the latter, and that it is not a very strong argument for Lu fitting better under Y than La does.

Even as it sucks as an argument [this really needs editing for academic tone], I would also point out that Sc-Y-La forms a triad (39 is the average of 21 and 57), just like Ca-Sr-Ba does (38 is the average of 20 and 56). Thus, claiming that Y-La-Ac doesn't form a triad while Y-Lu-Lr does is disingenuous and not the full story. Sc-Y-La forms a triad while Sc-Y-Lu doesn't.

Conduction band structures

Comments

• The authors say they undertook, "A systematic isochromat spectroscopic investigation of the bcc and hcp transition metals in the columns IIIA-VIA of the periodic table [9]…"
• In their letter they only depict measured isochromats for Hf, Lu, and La
• Reference 9 says "to be published"
• I can only find this for the group 3 metals: http://www.osti.gov/scitech/biblio/4523233, and for Ti, V, Cr, Zr, Nb, Mo, Hf, Ta, W, there is this (which looks like it'll be in German): http://link.springer.com/article/10.1007/BF01379873
• @Double sharp: Should we be concerned that the 4f⁰(5d6)³ electron configuration for La is essentially no different from that of Sc and Y? Even Lu is 4f¹⁴(5d6s)³. Looking at Jensen's 1982 article (Table 2) maybe it is the presence in La of what Jensen calls "low-lying nonhydrogenic f-orbitals" in La that rules it out from having a d-block like structure for its conduction band. I'm OK if this is so, as it has effectively nil practical relevance. Sandbh (talk) 06:13, 5 November 2016 (UTC)
  • This is the one argument by Jensen that I haven't yet found a way to counter. While declaring it irrelevant would be an attractive solution, the fact of the matter is that I would like to make the -La-Ac case as good as it could possibly be. From what I read about La's band structure, I have a difficult time seeing why there should be any 4f involvement at all, since 4f has not yet collapsed (that happens at Ce) and should be well above the Fermi level. However, reality seems to disagree. Double sharp (talk) 06:24, 5 November 2016 (UTC)
  • (See my comments on the superconductivity argument below. Admittedly the paper is from 1969.) Double sharp (talk) 06:41, 5 November 2016 (UTC)
    • Wait a minute; Merz and Ulmer are talking about the lack of d-electron character in the conduction band of La, not 4f involvement. Do you have your electron types crossed? Sandbh (talk) 10:50, 5 November 2016 (UTC)
      • Strangely enough, I find that in 1969 (see the superconductivity section) it was stated in a different paper that the band structures of La and Lu are essentially equivalent in having essentially no 4f character and being purely 5d¹6s². There would be a real difficulty here if La had no 5d character and was mainly a 4f6s² metal, but already two years later this point of view seems to not be upheld. Double sharp (talk) 11:23, 5 November 2016 (UTC)
• Hmm, I still don't follow what you're saying here, but I'll post something else to explain what I mean. In the meantime, I found this paper http://jetp.ac.ru/cgi-bin/dn/e_059_05_0995.pdf that says, "The conduction band of lanthanum is formed by two 6s electrons and one 5d electron [same as what Greenwood and Earnshaw say about most of the rest of the Ln]" and "These peculiar physical properties of lanthanum can be explained by a high density of states at the Fermi level, as is typical of d-transition metals…[italics added]" which seems to contradict what Merz and Ulmer found. Sandbh (talk) 04:21, 14 November 2016 (UTC)
• A 2016 paper http://file.scirp.org/pdf/WJCMP_2016020315144233.pdf, of uncertain reliability, discussing the negligible presence of f-character in La (p. 18) and noting that the 4f state lies ~5 eV above the Fermi level (which we already know, as I recall). Sandbh (talk) 05:54, 14 November 2016 (UTC)
  • Cool! Yes, I think I understand what you mean now. The only plausible difference there might be between La and Lu is 4f in the former vs the latter, but we find that this theoretically possible difference does not appear in reality. Double sharp (talk) 08:36, 14 November 2016 (UTC)

I suspect some of the p-block metals sitting on the metalloid frontier (esp. Bi, Po) might have unexpected conduction band structure, too. Sandbh (talk) 09:46, 15 November 2016 (UTC)

Task list

Ensure we have:

1. All the arguments listed here and their analyses
2. Redraft same into submission format
3. Check Double sharp's talk page for more recent arguments
4. Do we have any more arguments in our heads, that we haven't articulated yet?
5. Check e-mail discussions with Eric
6. Check R8R's page
7. Check citation formatting
8. Check for academic tone

Redrafting comments

Wow, just had a look at doing argument 4.3, Electron configurations. That one'll require a bit of thinking on how to approach it. Sandbh (talk) 00:49, 5 November 2016 (UTC)

What, something like 40 ♥'s to go? Sandbh (talk) 02:03, 5 November 2016 (UTC)

I need the power of your love and your hearts to write this submission! All of you are full of purity, truth, and f-electrons! (except lanthanum and actinium) Double sharp (talk) 13:41, 5 November 2016 (UTC)

LOL! On my ipad they look like puffed up red hearts, which is somewhat distracting. Sandbh (talk) 21:46, 5 November 2016 (UTC)

So, I assume that the structure will be: introduction, presentation and analysis of -Lu-Lr arguments; presentation and analysis of -La-Ac arguments; explanation of why we believe that the case of -La-Ac is more consistent with the principles of the periodic table as currently drawn? (The last part would use the condensed-phase electron configuration argument, as well as draw parallels between the statuses of Ca-Sr-Ba and La-Ac.) Double sharp (talk) 13:53, 5 November 2016 (UTC)

Yes, something quite close to that I'd expect. I'd probably add a conclusion. So we might have:

1. Introduction outlining our thesis
2. Presentation and analysis of -Lu-Lr arguments
3. Presentation and analysis of -La-Ac arguments
4. Weighing up the evidence and making a judgement that the case for -La-Ac is more consistent with the principles of the periodic table as currently drawn, highlighting the condensed-phase electron configuration argument, as well as parallels between the statuses of Ca-Sr-Ba and La-Ac
5. Conclusion reiterating our thesis

I expect that the structure will tend to look after itself after we have our arguments agreed and sorted into an logical progression. Sandbh (talk) 21:46, 5 November 2016 (UTC)

Oh, and kudos for your edits while I was in Z land! Sandbh (talk) 21:49, 5 November 2016 (UTC)

Thank you! Unfortunately Z land did not come quite as readily, so instead I spent some time in Z = 57 land instead. Double sharp (talk) 04:32, 6 November 2016 (UTC)

Groan! Sandbh (talk) 07:07, 6 November 2016 (UTC)

I just found that I wrote another presentation about this! (Look at Lanthanum#Position in the periodic table.)

Taking your advice "4. Do we have any more arguments in our heads, that we haven't articulated yet?", I've tried to summarise the series of logical steps that persuaded me away from -Lu-Lr and firmly to -La-Ac below. If anything here is not covered in the draft submission we could add it.

1. It is true that Lu is more similar than La to Y and that the Sc-Y-Lu trends parallel those later in the d-block better than the Sc-Y-La trends.
2. It is true that the electron configuration argument, as applied to gas-phase atoms is inconclusive as both La and Lu show a 5d differentiating electron from Ba and Yb respectively.
3. A Sc-Y-Lu table seems to show fewer discrepancies between real and ideal electron configurations.
4. However, the trend argument ignores the typically increasing basicity down the periodic table, by which one would expect La to be larger than Y and therefore to behave somewhat differently. For instance, it is well-known that Ca, Sr, and Ba show distinct differences from Be and Mg, but they are kept in the same group because not only does this result in a common set of electron configurations, but also because moving Be and Mg to over Zn means that the periodic table predicts more wrong electron configurations in the condensed phase (most relevant for chemistry).
5. The lanthanide contraction happens only after La and goes on from Ce to Lu. Thus if group 3 is Sc-Y-La, its differences in trends from Ti-Zr-Hf, V-Nb-Ta, etc. can easily be explained by the fact that all these later groups come after the lanthanide contraction, but group 3 comes before it.
6. Excluding La or Lu on the basis of different types of bonding or trends does not conform to the principles of the periodic table, which are based primarily on electron configurations and increasing size (and concomitant basicity and metallicity) going down the table. At the best they are merely a tipping-point argument that could be used to resolve a deadlock if one existed. If they were really a basic principle of the table, group 16 would have to be split, as while SO₂ forms simple covalent molecules, SeO₂ and TeO₂ form giant covalent lattices and PoO₂ is an ionic solid.
7. La does not show any clear 4f character at all. All properties that have been attributed to 4f character in La have simpler explanations that do not require positing 4f involvement. As a result, giving f-block status to two elements with no f-character at all (La and Ac) is questionable. (Th shows f-character in the solid phase, as well as in the fact that the Th³⁺ ion has a [Rn]5f¹ configuration.)
8. If you start the f-block at La and end it at Yb, you start it when the f-orbitals are not yet chemically active and end it while they still are. This has no parallel anywhere else in the periodic table. On the other hand, if you start the f-block at Ce and end it at Lu, you start it only when the f-orbitals drop down in energy level enough to be used, and end it after they have been filled with fourteen more electrons. This is similar to the situation in the d-block from Sc to Zn, and in the p-block from B to Ne. Even if La and Ac show some "supervalent hybridisation", so do Ca, Sr, and Ba, and since those are not considered d-block elements neither should La and Ac be considered f-block elements. Therefore the Sc-Y-La placement is more consistent with the principles of the periodic table as it is usually drawn today.
9. The trends going down Sc-Y-La and Sc-Y-Lu are both compelling, but the former tend to follow the group 1 and 2 trends more and the latter tends to follow the group 4 and 5 trends more. However, there is a clear, discontinuous change in chemical character from group 3 to 4 that weakens the latter analogy.
   • For instance, while Sc, Y, the lanthanides, aad the actinides can form trivalent aqua ions which are not appreciably hydrolysed, Ti, Zr, Hf, and Rf (and even Th) cannot form similar tetravalent aqua ions without them being hydrolysed significantly.
   • As another example, while KCl, CaCl₂, and ScCl₃ are ionic, TiCl₄ is a covalent molecular liquid, because the +4 charge on Ti is just too high for the ionic bond model to be a satisfactory description of what happens any more.
   • Finally, the chemistry of the rare earths is most easily described as those of trivalent relatives of the alkaline earth metals, whereas Cotton and Wilkinson feel the need to separate group 3 and the lanthanides completely from the rest of the transition metals because the chemical differences are just too great. While Sc, Y, La, and Lu do not form simple ions in any state lower than +3, Ti, Zr, and Hf do form simple ions in the +3 state (lower than the group +4 state). The rare earths are thus very atypical transition metals at best and are more related chemically to the main-group elements (indeed R. Bruce King defines them as such).
   • Hence, analogies to the left side of group 3 are felt to be more compelling than those to the right side of group 3.
10. Finally, in the condensed phase, the lanthanides are primarily fⁿds² and not fⁿ⁺¹s². Sc-Y-La gives the former prediction while Sc-Y-Lu gives the latter one. Furthermore, Sc-Y-Lu, with the assumption that 4f is in the core (not unreasonable and quite true to a first approximation), makes it very difficult to explain the trivalence characteristic of the lanthanides, while Sc-Y-La handles this easily.

Double sharp (talk) 09:59, 6 November 2016 (UTC)

BTW, we'll have to write section 4 carefully to avoid redundancy. I suggest that we go into specific analyses of each argument in sections 2 and 3, but in section 4 we should instead look at the degree of convincingness of each type of evidence. There we can get to the bottom of what exactly the basic principles of the periodic table as it is usually drawn are, and then use those to argue for -La-Ac. Double sharp (talk) 10:07, 6 November 2016 (UTC)

Sitrep 13 Nov

(1) I think we have the structure in place and each argument for Lu-Lr or La-Ac has some content. (2) I guess now we need to check and tune, if required, each argument, and check to see that we haven't missed or cut any arguments or significant content. So far I've been mainly focussed on (1). Sandbh (talk) 04:06, 13 November 2016 (UTC)

Sitrep 15 Nov

OK, I think I'm much happier now with our response to the conduction band argument. Onwards with checking and tuning (after a coffee). Sandbh (talk) 09:42, 15 November 2016 (UTC)