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D. H. Rouvray and R. B. King (eds.): The Periodic Table: Into the 21st Century. Philadelphia/PA: Research Studies Press, Baldock/Hfsh & Institute of Physics Publishing, 2004, xx + 396 pp., ISBN: 0-86380-292-3, hardcover, ~75 USD. This book consists of ‘‘expanded versions of 13 plenary lectures given at the Second Harry Wiener International Memorial Conference’’, held near Banff, Canada, in July 2003, to celebrate the invention of Periodic Tables (PTs) of chemical elements about 135-years ago. The title ‘‘The Periodic Table: Into the 21st Century’’ suggests that the aim of the conference should have been to describe and discuss current and future research programs on PTs. It is therefore somewhat surprising to find many chapters in this volume that emphasize the previous history of and opinions on PTs, particularly 19th century history. There are also some surveys of more recent historical aspects of theoretical physics, and reviews of viewpoints expressed in the 20th century by material scientists and by chemists interested in pedagogical aspects of the PT. Descriptions of relevant current theoretical research and of suggestions for future research in the 21st century are relatively rare. It is mentioned by M.R. Kibler on page 312 that the volume under review is the first one of a two volume set of papers delivered at the conference. The editors do not mention this possibility, but there is an internet listing of a book by the editors with the title ‘‘The Mathematics of the Periodic Table’’ (the most recent publishing date being middle 2006) by Nova Publishers (ISBN: 1-59454-259-7). The description of the book lists a number of topics one would have expected to find in the book under review, moreover, one third of the authors have articles also in the ‘‘first’’ volume. Others were apparently at the conference but did not contribute to the volume under review. Foundations of Chemistry (2006) 8:293–303 DOI 10.1007/s10698-006-9014-x


Springer 2006

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Although several of the papers in the new book are available from individual authors, they will not be discussed further in this review. The first three chapters, about thirty percent of the total number of pages, are devoted almost entirely to the prehistory and to the invention of PTs in the 19th century. The authors (D.H. Rouvray, M.D. Gordin and M. Kaji) are all well known for their previous publications on this topic and here they summarize their work. Mendeleev (this spelling is used in the book; we also refer to lanthanides and actinides, instead of lanthanoids and actinoids, because those are the terms used in most chapters), they agree, is not the only person who deserves credit for the invention of the PT, but they disagree on which of the possible coinventors should be given credit as such. Rouvray, chapter 1, reiterates his viewpoint, shared by many, that William Odling as an early proponent of the PT deserves more credit than he is usually given. In fact, his table published in 1864 and reproduced on page 24 and again on page 95, is almost identical to the reproduction of MendeleevÕs 1869 table shown on pages 29 and 105. On the other hand, Kaji claims, Odling deserves no credit because ‘‘he barely understood the meaning of his table and considered it only as a convenient way to arrange the elements’’ (p. 112). GordinÕs article, chapter 2, is devoted almost entirely to Mendeleev and concentrates on the details of how Mendeleev himself established his international reputation. For example, on page 61, Gordin writes that the ‘‘article that truly made MendeleevÕs name’’ was on gallium and was published in French in Comptes Rendus (1875, vol. 81, pp. 969–972). There is evidence that once Mendeleev had established his reputation in Russia, he set out deliberately to acquire an international reputation by publishing his work in foreign journals. He was also not shy in claiming priority for his work, something that the majority of his competitors did not do, to their future cost. Gordin is also the only one of the three historians to discuss the problems that Mendeleev initially encountered with respect to incorporating the inert gases, to the discovery of radioactivity and to the existence of the chemical ether into his PT. His final

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1903 version is shown on page 78. This PT shows a zero group of nine members (if we count two blank spaces), the first two members of which are the ether and LockyerÕs postulated element coronium, both with atomic weights less than that of hydrogen. The early development of the PT is also briefly outlined by M. Laing in chapter 4. He reviews ThomsenÕs table (1895), and the introduction of the nuclear charge by Moseley and Bohr, before he passes on to a critical discussion of some of his favorite modern tables. He ends with an interesting outline of his views on what he considers to be particularly useful PTs and describes his own modified form. He quite rightly states that the PTs are man-made arrangements of the elements displaying properties and relationships. They are not numerology, but are working tools for the practicing chemist, so that it is unlikely that just one PT will satisfy every one. However, on page 136 he states ‘‘How can one possibly believe that it is rational to expect that all of the chemical reactions of an element can be dictated by one integer Z, its atomic number?’’ Surely that is one of the ultimate aims of modern quantum chemistry! By the end of the 20th century many user-friendly molecular structure computer programs became available. Many of these can be used for atoms, and for this purpose all that is needed as input is the atomic number. The total energy, the orbital energies and many atomic properties will then be calculated very quickly. To do the same for molecules, it is only necessary to specify the atomic number of each constituent atom and a rough starting geometry in order to produce a predicted geometry and many molecular properties. There is no doubt that in the 21st century many improvements of existing procedures and the development of new ones, especially in the area of predicting and explaining chemical reactions, will become even more commonplace than they are now. E. Scerri in chapter 5 starts with another brief (6 pages) history of the PT. He chooses two modern tables as his favorites. He gives his formal reasons for this choice, putting particular emphasis on the position of hydrogen and helium. He assigns the start of each period by some number (n + l)

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rather than by referring to the physically and chemically relevant filled inert core shells, i.e. 1s2 and ns2np6. This numerological approach, sometimes referred to as the Madelung rule, has become a center of attention of several philosophical groups in the latter part of the 20th century. This work is described and discussed in considerable detail in chapters 11 and 12, and we defer further comment until these chapters are reviewed below. Later in his chapter, Scerri describes MendeleevÕs views on the nature of the elements and draws the attention of ordinary chemists to the macroscopic difference between MendeleevÕs (and PanethÕs) concepts of ‘‘Basic Elements’’ and elementary ‘‘Simple Substances’’. However, this distinction is not carried over to the corresponding microscopic difference between chemically bound atoms and free atoms in vacuum. He concludes by suggesting that ‘‘the finest PT of all may lie, like the abstract elements, in the realm of ‘‘unobservables’’’’. Since this and other philosophical approaches to the PT are a matter of considerable discussion in the current literature, we reluctantly refrain from further comment. Before discussing the more theoretical papers, it seems appropriate to review the four chapters by G.W. RaynerCanham, R.B. King, H.C. Aspinall and P.J. Karol. In chapter 6, Rayner-Canham discusses the properties which actually deal with ‘‘chemical Richness of Periodic Patterns’’. He gives many examples of group and periodic trends with emphasis on anomalous instances, diagonal relationships and examples of LaingÕs ‘‘knightÕs move’’. However, he makes no mention of recent chemometric studies of periodicities, nor of the structural maps currently popular among solid state and material chemists. On the other hand, he brings up to date some of the ideas that were once commonplace in inorganic textbooks, but which seem, in modern books, to have been removed to make room for more fashionable concepts. For example, he includes ideas such as pseudo-elements, the similarity of the early actinides to the transition metals, and the importance of the isoelectronic principle. Sometimes he seems to take his analogies too far, but that in itself can be made into an important teaching point. On the whole he achieves his goal of bringing

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chemists back to thinking about chemistry relationships rather than concentrating on the electronic structure of independent atoms. His version of the PT appears as colorplate 2, which uses color to emphasize many of the relationships discussed in the text. Next, in chapter 7, King attempts to catch the interest of both metallurgists and chemists by demonstrating how the PT could be very valuable in designing new intermetallic alloys and in understanding their properties. He takes as his favorite ‘‘The metallurgists PT’’ introduced by H.E. Stone in 1979. Stone divided the PT into four sections by vertical lines or divides: the ionic, the covalent, the composite, and the transition metal divides. King gives examples of how the divides may be used to choose the atomic components for semiconductors and conductors in designing ‘‘electron compound’’ intermetallics and in understanding the structure and alloying properties of transition metals and the lanthanides. Considering the enormous current activity in these fields, it is rather strange and regrettable that the only references to StoneÕs PT, uncovered by a citation search, are 10 in number (5 by Stone himself and 5 by King). It should be noted that Linus Pauling published many papers on intermetallic bonding throughout his whole career and many of his ideas are very similar to those of Stone, although written from a more theoretical perspective. For example, in a 1950 paper in the Proc. Natl. Acad. Sci. USA (36: 533–538) on electron transfer between hypoelectronic and hyperelectronic atoms, Pauling gives a related classification based on the PT. Although this paper received more citations than StoneÕs did, the number is still very small, considering the importance of the insights it contains. King completes his chapter by discussing some recent developments in the chemistry of intermetallic phases and metal cluster anions, stressing the importance of the tetrachotomous classification of elements into metals, meta-metals, semi-metals and non-metals introduced by Klemm more than half a century ago. King also reviews attempts to rationalize the structure and bonding in the metal cluster compounds, especially the Zintl-Klemm concept, and the Wade-Mingos rules, though he does not mention

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the systematics of Pettifor. With the current growing interest in nanotechnology and the need for new ‘‘quantum sized particles’’, there is no doubt that interest and knowledge concerning the aspects of the PT covered in this chapter will skyrocket in the 21st century. In chapter 8, Aspinall (who does not appear in the photograph of participants, plate 8) discusses the history and periodic trends of the lanthanide elements with particular attention to the preparation of organometallic lanthanide compounds of oxidation states II and III, together with their uses as catalysts. Karol in chapter 9 is one of the few contributors in the book who comments on the future of the PT. However, once again the chapter is largely historical, especially with respect to the space allotted to the description of the earlier theories of the nucleus. By contrast the space filled by the description of work on the synthesis of superheavy elements and how the results were proved to be correct is relatively small. One may wonder why yet another picture of the first thermonuclear detonation at Eniwetok Atoll should take precedence over recent work on superheavy element production. Several important diagrams, especially Figures 13 and 14, appear but are referred to in the text only briefly. Fortunately Karol has a paper (J. Chem. Educ. 2002, 79: 60–63), which addresses in more detail some of the questions raised in the chapter. The last part of the chapter (nine pages) is devoted to the very interesting, but probably very little known history, called by Karol a ‘‘soap opera’’, of the various priority claims and names choices for the transfermium elements. This section draws attention to the establishment by IUPAC of a ‘‘Joint Working Party (JWP)’’, chaired by Karol, given the unenviable task of evaluating the validity and priority of the many claims now appearing in the literature in this field. The technical reports issued by the JWP, such as the one published in 2003 and referred to in the chapter as Ref. [16], discuss in detail the claims associated with the ‘‘discoveries’’ of elements 110, 111, 112, 114, 116 and 118. In the meantime elements 113 and 115 have also been accepted, but names for elements from 112 onwards have not been agreed on. The JWP reports reference all the relevant literature, with

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comments, and enable the general reader to keep abreast on what is going on in the 21st century in this very active and controversial area of research. It should be noted that some of the other chapters in the volume under review give data, which contradict the claims of the JWP. The following three chapters by K. Balasubramanian, M.R. Kibler and V.N. Ostrovsky are of theoretical nature. Chapter 10 by Balasubramanian opens with a very clear qualitative description of the nature of relativistic phenomena in chemistry and on the relative magnitude these effects have on energy levels and spatial distributions of the orbitals of atoms and molecules. Balasubramanian shows that explanations and predictions of the properties of the heavier elements, say with atomic numbers greater than Z = 30, are bound to be inadequate if they do not take into consideration both relativistic and electron correlation effects. The author achieves his aims without using complex mathematics, but does give many literature references, where the computational details may be found. However, more than 40% of the 114 references are to books and papers by the author, making the chapter a highly personal one. Nevertheless he presents numerous examples of apparent anomalous properties of the heavier transition metals due to relativistic effects. He also explains very convincingly why, because of relativistic effects, the sixth row p-block elements (Tl-At) exhibit fewer valences and weaker bonding than their lighter analogues, while the opposite tendency holds for the d-block. The next section describes his recent calculations on the late actinides (nobelium and lawrencium), which offer an explanation of their unusual non-actinide properties. The final section of 20 pages describes the authorÕs calculations on the superheavy elements (Z = 105–114). He claims that relativistic effects will dominate their bonding properties to the extent that they will not follow the naively expected regular periodic trends, concentrating on his very recent calculations on E113-H (eka-thallium hydride). He predicts the yet unknown compound, on a purely ab initio basis, to exhibit properties different from those of thallium hydride. That is because the energy levels are so altered by relativistic effects that even the correlation energy contribution

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to the bonding in the former molecule is quite different from that in the latter, and that is already considerably different from the properties of its lighter analogs B, Al, Ga and In. Other workers are performing similar calculations and it is recommended that the interested reader should consult, in addition to the chapter under review, a recent book devoted entirely to a description of the different theoretical methods available, and to recent results on the properties of the superheavy elements and their compounds, produced by methods other than those used by Balasubramanian. (‘‘Theoretical Chemistry and Physics of Heavy and Superheavy Elements’’, ed. by U. Kaldor and S. Wilson, Kluwer Academic, 2003). There is no doubt that, as experimental trapping techniques improve, one can expect that in the 21st century more and more heavier atoms will be synthesized and at least some of their properties observed. There is also no doubt that relativistic calculations of the type described by Balasubramanian and others will most certainly play an important role in assigning these new elements to their rightful places in the PT. Since relativistic effects increase in a strongly angular-momentum dependent manner with a higher power of Z, chemists must recognize that both extrapolations of empirical chemical results garnered by observations on the lighter elements and numerological playing with nonrelativistic quantum numbers, are bound to fail. The topological structure of chemically useful PTs for the region Z > 100 is yet unknown. Successful speculations can only be built along a two-step path: first more empirical data obtained by further quantum computations and their corroboration by experimental data, and second, a more detailed analysis of the known and future numerical data with respect to the variation of orbital energies, orbital radii, bond energies etc. with nuclear charge and with group number. Knowledge and understanding of the ‘‘Periodicity of Relativity in the lower part of the Periodic Table’’ will surely become a goal in the 21st century. Kibler (chapter 11) briefly reviews a number of topics relevant to his own work on the PT. Four pages are devoted to the history of the PT ‘‘from antiquity to 2003’’, twelve pages to the

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history of theories of subnuclear particle physics and four pages to an attempt to give enough group theory to enable the specialist to understand the rest of the chapter. This latter part describes some of the many attempts to use group theoretical methods to represent the structure of PTs as perceived by mathematical physicists and philosophers. Kibler reviews his own work on using formal group theory to justify the so-called ‘‘phenomenological Madelung (n + l) rule’’ and he also outlines plans for a new project for the future, using the principles of group theory to estimate some atomic properties. This project has been described in more detail in a recent publication ‘‘On the Use of the Group SO (4,2) in Atomic and Molecular Physics’’ (Mol. Phys. 2004, 102: 1221–1229), and in a contribution to the companion volume mentioned above (Chapter 11: ‘‘A Group-Theoretical Approach to the Periodic Table: Old and New Developments’’). Kibler has named his new project the ‘‘KGR program’’ after the Kananaskis Guest Ranch, which hosted the PT conference at which he first revealed his proposal. Ostrovsky, in chapter 12, gives a survey of ‘‘essential developments concerning the quantum theory of the PT’’. He has published similar reviews elsewhere. These reviews are devoted to describing attempts, including his own many contributions, to explain the Madelung rule for free atoms by estimating the one-electron spectra of approximate models using modifications of the Thomas-Fermi potential. Ostrovsky describes the development of orbital occupations of the lowest spin-orbit levels of free neutral atoms when going from one atom to the one with the next higher Z. He reminds the chemists that this topic is a typically physical one and he traces the history of the rule back to its Russian origin around 1930. Although he mentions that there are some 20 exceptions to the (n + l) rule, he does not explicitly mention any details on how relativistic many-particle approaches have already provided us with a full understanding of all these so-called exceptions. As a physicist and like some philosophers, he does not seem to be much interested in chemical questions, concerning the properties of chemically bound atoms, although it is these, which determine

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the molecular properties and the structure of the chemical periodic system. Possibly this is because the approximate methods he favors have not yet been shown to be applicable to problems concerning the bonding, shape and properties of molecules, problems which are of major concern to most chemists. The final chapter 13 by J.R. Diaz reviews his own extensive and very specialized work on his ‘‘Formula Periodic Table’’ (FPT) for benzenoid and other classes of hydrocarbons. This work uses molecular graph theory to represent the hydrocarbons and combines these ideas with the useful mnemonic idea of organizing and understanding property trends in large classes of molecules by tabular arrangements. Benzenoid hydrocarbons are in some sense the most abundant class of organic compounds in the known universe. So DiazÕ systematization has already shown itself to be of great value to scientists working with such large classes, and its value will likely increase in the present century as chemists become more aware of its potential. In trying to survey both the history and current applications, Diaz has perhaps not spent enough time on the fundamentals of how his molecular PTs are constructed and how they are related to the PTs of chemical elements. Fortunately, he has just published a ‘‘Tutorial Review’’ of the topic (Austral. J. Chem. 2004, 57: 1039–1049), which clearly answers these questions as well as explains more technical terms such as leap frogging, which enables the synthetic chemist to rapidly deduce the most stable benzenoid hydrocarbons without knowing the structures of the thousands of other isomers. He also explains the significance of edge effects and of the ‘‘topological paradigm’’, and how periodicity of molecular properties appears in his tables. Both articles by Diaz give examples how tables can be used to make useful working hypotheses on chemical reactivities and relative stabilities. There is significant potential in this little-known technique. Although unrelated to work on the periodic system of elements described in the earlier chapters, this chapter probably has a better right to appear in a book commemorating the ‘‘chemist and polymath Harry Wiener’’ than some of the historical content of some of the earlier

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chapters, especially as no other articles on information theory and the PT are contained in the book. The chapter by chapter review we have undertaken shows that the selection of philosophical and scientific topics is somewhat ,personalÕ and is restricted to the conference attendees. Moreover each chapter was apparently written independently of the coverage in the other chapters. In total the book collects a multitude of 20th century opinions on the periodic system, some of which are overlapping. It offers a few constructive ideas concerning topics for fruitful research in the 21st century. In this indirect sense, the title of the book is appropriate. The absence of an index is a real disadvantage, not only in finding where a particular topic is, but also in assessing how much overlap there is between different chapters and even whether a particular topic has been covered at all. Despite these shortcomings the book can be recommended to the tyro interested in learning about the history of the PT and some ideas of current thinking concerning certain aspects of the PT. JOHN E. BLOOR

Department of Chemistry, University of Tennessee 7226 Austin Park Lane, Knoxville, TN 37920, USA E-mail: [email protected] W. H. EUGEN SCHWARZ

Theoretical Chemistry Groups, University Siegen D-57068 Siegen, Germany and Jiao Tong University 200240 Shanghai, China E-mail: [email protected]