A Quantum Chemical Dialogue Mediated by Textbooks: Pauling's "The Nature of the Chemical Bond" and...

A Quantum Chemical Dialogue Mediated by Textbooks: Pauling's "The Nature of the ChemicalBond" and Coulson's "Valence"Author(s): Ana SimõesSource: Notes and Records of the Royal Society of London, Vol. 62, No. 3 (Sep. 20, 2008), pp.259-269Published by: The Royal SocietyStable URL: http://www.jstor.org/stable/20462677 .

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NOTES & RECORDS Notes Rec. R. Soc. (2008) 62, 259-269

-OF THE ROYAL doi: 10. 1098/rsnr.2007.005 1 SOCIETY Published online 9 May 2008

A QUANTUM CHEMICAL DIALOGUE MEDIATED BY TEXTBOOKS: PAULING'S THE NATURE OF THE CHEMICAL BOND

AND COULSON'S VALENCE

by

ANA SIMOES*

Center for the History of Science of the University of Lisbon (CHCUL),

Faculty of Sciences, University of Lisbon, Campo Grande, C4, Piso 3,

1749-016 Lisboa, Portugal

In this paper I look at Coulson' s Valence not as the textbook that ended the hegemonic reign of Pauling' s The nature of the chemical bond, but as the outcome of an ongoing conversation, either literal or metaphorical, between Pauling and Coulson, in which each scientist was responding to the other, agreeing or disagreeing with him, in the process revising his ideas, and writing the successive editions of his textbook. Far from merely expository devices, these textbooks were central pieces in an intellectual dialogue involving their authors about scientific theories and the status of concepts and, to a certain extent, about their competing philosophies of science.

Keywords: history; quantum; chemistry; C. A. Coulson; Linus Pauling; textbooks

INTRODUCTION

In an obituary notice, the Nobel Prize winner Roald Hoffman evaluated the contributions to quantum chemistry of the trio Linus Pauling, Robert Sanderson Mulliken and Charles Alfred Coulson in the following manner:

American and British chemists had secured a place for quantum mechanics in chemistry, through the charismatic exposition of Linus Pauling, the quieter and deep reflections of Robert Mulliken, and the elegant and perceptive teaching of Charles Coulson.1

Not surprisingly, he highlighted in both Pauling and Coulson their excellence as communicators while he stressed Mulliken's qualities as a scientific thinker. Certainly, all three were builders of the discipline of quantum chemistry, but, of the three, only Pauling and Coulson excelled as teachers, textbook writers, and popularizers. In fact, in the standard

history of quantum chemistry, when assessing the reasons behind the ready acceptance of the

valence-bond (VB) method pushed forward by Pauling, N. V. Sidgwick and G. Wheland when compared with the molecular orbital (MO) method developed by Mulliken and J. E. Lennard-Jones and extended by Coulson, historians acknowledge that initially there

*[email protected]

259 This journal is ?) 2008 The Royal Society



260 A. Simoes

were no empirical or predictive reasons to account for the early success of the VB method, which owed much to the persuasiveness of Pauling as a teacher and textbook writer. Specifically, Pauling's textbook The nature of the chemical bond (1st edition 1939) was never challenged by any textbook written by Mulliken, who in fact wrote none. It was rivalled only by Coulson's Valence (1st edition 1952), a textbook that was published more than a decade later.

Textbooks are privileged means of conveying science to students, of training them in the skills of the trade, and they often arise as the end product of years of lecturing to successive classes of students. Viewed from this perspective, they are reified conversations between teacher and students. However, textbooks have been presented as dogmatic expositions of science, stripped away of all novelty, far away from the turmoil of science in the making; in sum, privileged means of indoctrinating students in the practices of normal science. Historians of science have challenged this view.2 They have claimed that the distinction between science in the making and science ready-made is often not so clear cut, and therefore textbooks should not be seen as neutral vehicles of normal science.

In this paper I look at Coulson's Valence not as the textbook that ended the hegemonic reign of Pauling's The nature of the chemical bond, but as the outcome of an ongoing conversation,3 either literal or metaphorical, between Pauling and Coulson, in which each scientist was responding to the other, agreeing or disagreeing with him, in the process revising his ideas, and writing the successive editions of his textbook. To support my analysis of the successive editions of both textbooks I correlate them with other relevant outputs by both authors (review papers, correspondence and manuscripts). I will centre the discussion on the concept of resonance introduced by Pauling to explain the properties of molecules such as benzene for which no single VB structure accounts for its chemical behaviour.

Far from being merely expository devices,4 these textbooks were central pieces in an intellectual dialogue involving their authors about science in the making, the role of scientific theories and the status of concepts and, to a certain extent, about their competing philosophies of science. From this new perspective, both textbooks are seen not just as reified conversations between teacher and students but also as reified conversations between both authors who in the process sharpened their views about quantum chemistry (and about science) and afterwards conveyed them to readers and students. As chemistry has often been claimed to be a science in which conversations have a prominent role,5 this new vantage point looks at textbooks as conversational devices, in many respects at the same level as conversations central to the forging of science itself.

ENTANGLED TRAJECTORIES: LINUS PAULING, CHARLES ALFRED COULSON AND THEIR TEXTBOOKS

Pauling 's first attempt at textbook writing

Although there has been a tendency to associate Pauling with the articulation and lifelong defence of the VB method, it is instructive to point out that in the early years of his career, Pauling explored the possibilities of molecular orbitals (binuclear orbitals), first in the framework of the old quantum theory and then in the context of the new quantum mechanics.6 Although this early avenue was abandoned, Pauling continued to look for a quantum mechanical explanation of the chemical bond. It was finally articulated in the famous series of seven papers, 'The nature of the chemical bond' (1931-33), in which notions such as hybridization, maximum overlapping, and resonance between VB structures were put forward.



A quantum chemical dialogue mediated by textbooks 261

He was then a full professor at California Institute of Technology. At about the same time,

Mulliken was exploring in Chicago the same problem from a totally different perspective. It

amounted to a complete abandonment of the old notion of chemical bonds and its replacement

by the alternative conception of molecular orbitals (in the series 'Electronic structure of

polyatomic molecules and valence', 1932-35). Despite these seemingly opposite viewpoints,

which came to be known respectively as the VB and the MO theories, the fact of the matter was

that, no later than 1935, a review paper by John H. Van Vleck and A. Sherman proved both

approaches to be mathematically equivalent.7 Having this proof in mind, their differences were

accordingly to be found at the ideological level, a fact that Mulliken noted soon when he

poignantly characterized the VB theory as following 'the ideology of chemistry'.8 It is in this context that one should consider the failed attempt of Pauling and his former

student Wheland at writing a textbook, Quantum mechanics of organic molecules, in which

they planned to offer an extensive comparison of the VB and the MO methods. During the

academic year 1936/37 they outlined its chapters and allocated tasks to each co-author.

Wheland prepared the introductory chapters based on the VB method, and Pauling was in

charge of the chapters on the comparison of both methods. Wheland's part was soon

completed and revised by Pauling, but Pauling never managed to deliver his share of the

project.9 It is interesting to speculate on the reasons behind the failure of the only project for

which we have evidence in which Pauling was willing to take seriously the MO method and to

contrast the performance of both the VB and the MO methods when dealing with organic

molecules. Certainly, Pauling's attention was then drifting towards applications to larger

molecules of biological interest, but more importantly this failure hints at Pauling's inability

to stand on the MO reference frame. This incapacity was certainly the outcome of the

articulation of a chemical theory centred on the concept of resonance, the correlated belief

that resonance stood for as real a molecular phenomenon as any other molecular property, and

that resonance theory was as much a chemist's artefact as any other theory.

The first and second editions of The nature of the chemical bond

This much was discussed in the first edition of The nature of the chemical bond (1939), which

was organized around the central notion of resonance.10 In this way, resonance, which Pauling

appropriated from the new quantum mechanics, together with the major questions discussed

in his papers, was presented to an enlarged audience of fellow chemists and students.

Furthermore, the book stood as the foundation stone of a program of reformation of

chemistry from the standpoint of the theory of resonance, which was to become Pauling's

hallmark and was outlined in a practical way in textbooks such as General chemistry (1947)11 and College chemistry (1950).12 Quantum chemistry notwithstanding, the teaching of

chemistry should in the first place get students to develop a 'feeling for chemistry', through

contact with chemical compounds and their properties. At the introductory level the teaching

of chemistry should not rely on extensive mathematical apparatus but should depend on

traditional structural notions such as chemical bonds. And the idea of resonance was

introduced as an embodiment of former structural ideas.

Pauling was aware of the difficulties faced by chemists in understanding such unfamiliar

concepts as the quantum-mechanical concept of resonance and the resonance of molecules

between several VB structures. He noted the existence of an 'element of arbitrariness' in the

use of the concept of resonance as a result of the choice of canonical structures in discussing

the state of the system, but he argued forcefully that 'the convenience and usefulness of

the concept of resonance in the discussion of chemical problems are so as to make the



262 A. Simoes

disadvantage of the element of arbitrariness of little significance."93 This, as he repeatedly stated, was his constructive criterion for theory building in chemistry. Besides, he reminded his readers that an equivalent element of arbitrariness occurred in essentially the same way in the classical resonance phenomenon.

Finally, he contrasted resonance with traditional chemical concepts such as mesomerism and tautomerism and discussed the reality of canonical structures. Even such a clear and succinct writer as Pauling could not at times avoid making apparently contradictory statements. As to the relation between resonance and tautomerism, Pauling sometimes seemed to be claiming that they were the same: 'There is no sharp distinction which can be

made between tautomerism and resonance',14 and at others that they were distinct: 'It is convenient in practice to make a distinction between the two which is applicable to all except the border-line cases',15 differing in the following way:

Whereas a tautomeric substance is a mixture of two types of molecules, differing in configuration, in general the molecules of a substance showing electronic resonance are all alike in configuration and structure.16

The same ambiguity arose in discussing the reality of different canonical structures. Is it the case that the two Kekule structures associated with the benzene molecule are real? Pauling claimed that 'there is one sense in which this question may be answered in the affirmative'",' but immediately added:

the answer is definitely negative if the usual chemical significance is attributed to the structures. A substance showing resonance between two or more VB structures does not contain molecules with the configurations and properties usually associated with these structures. 1 8

Having these linguistic ambiguities in mind, one cannot but wonder about their repercussion in the subsequent arguments over the significance of resonance.

The immediate success of The nature of the chemical bond was the result of several factors, including the assertiveness of physical chemistry in the USA, of which G. N. Lewis was one of the exponents and to whom the book was dedicated, the articulate expression of American pragmatism and operationalism, and the failure of alternative attempts at building a theory of the chemical bond by the German physicists W. Heitler and F. London. A second edition succeeded the first one, in the following year; the latter was merely updated to include very recent determinations of structures of several especially interesting molecules and crystals.19

However, since the first edition it had become clear for some readers that Pauling's textbook pushed forward a monolithic view of quantum chemistry. This is patent from the conclusion of the review offered by R. Mayer. He discouragingly noted:

It is unfortunate that this treatise will almost certainly tend to fix, even more than has already been done by the author's excellent papers, the viewpoint of most chemists on this, and only this one, approach to the problem of the chemical bond. It appears likely that the H-L-S-P [Heitler-London-Slater-Pauling] method will entirely eclipse, in the minds of chemists, the single electron molecular orbital picture, not primarily by virtue of its greater applicability or usefulness, but solely by the brilliance of its presentation.20

To reverse this situation was not an easy task. Mayer ventured that another book on the same subject, using the same examples but emphasizing alternative methods, should help in the process, but he predicted that it would be hard to emulate the clarity and simplicity of Pauling's almost exemplary presentation. Writing such a book proved to be within the grasp of Coulson.




Table 1. Chronology of Pauling's successive editions of The nature of the chemical bond, Coulson's successive editions of Valence, related publications, and correspondence between Pauling and Coulson on Coulson's first edition of Valence.

participants publications dates

Pauling The nature of the chemical bond, 1st edition 1939 Pauling The nature of the chemical bond, 2nd edition 1940 Coulson 'Quantum theory of the chemical bond' 1941 Coulson 'Representation of simple molecules by mol- 1947

ecular orbitals'; 'Meaning of resonance' Pauling 'The place of chemistry in the integration of 1950

the sciences' Coulson Coulson starts writing Valence in London 1947-51 Coulson Valence, 1st edition 1952 Pauling Review of Valence 6 September 1952 Correspondence between Pauling and Coulson Letter, Coulson to Pauling 8 September 1952

Letter, Pauling to Coulson 25 September 1952 Letter, Pauling to Coulson 4 November 1952 Letter, Coulson to Pauling 14 July 1953 Letter, Pauling to Coulson 12 September 1953

Pauling Nobel lecture, 'Modem structural chemistry' 11 December 1954 Pauling 'The nature of the theory of resonance' 1956 Pauling The nature of the chemical bond, 3rd edition 1960 Coulson Valence, 2nd edition 1961 Pauling The chemical bond 1967

Responding to Pauling: the chemical bond in the molecular orbital context

A mere two years after the first edition of The nature of the chemical bond came out, Coulson made his first incursion into textbook writing, at the same time extending the MO method with characteristic verve (table 1). The mathematization of quantum chemistry was to become his hallmark. Away from the centre, isolated in Dundee during wartime and still at the beginning of a university career, Coulson delivered a little book, Waves, in which he explored the unifying power of mathematics in treating wave phenomena. He continued writing textbooks until the very end of his life. The textbook Electricity followed (1948), then Valence (1952, 1st edition), certainly his most renowned textbook, and finally The shape and structure of molecules (1973).21

At the same time, as if warming up to deliver Valence, Coulson began articulating a response to Pauling's programme outlined in The nature of the chemical bond. In a paper deliberately called 'Quantum theory of the chemical bond' (1941) Coulson appropriated Pauling' s concepts of hybridization and of maximum overlapping and translated them into the language of MO.22 Whereas Mulliken was adamant that there was no such thing as a chemical bond, for Coulson MO theory did not have to abandon a pictorial interpretation of chemical bonds. On the contrary! He filled his paper with

diagrams, which later became familiar to any college chemistry student, depicting the formation of the MO in water, the formation of 'double-streamers' in ethylene, and the formation of the chemical bonds in benzene depicted by what came to be known as the 'doughnut' model. He went on to explore the notion of the chemical bond in the framework of MO,23 at the same time as he became increasingly critical of the notion of resonance,24 in the sense that, for him, resonance was not definitely a molecular property but just a heuristic device.



264 A. Simo5es

Valence, which Coulson began writing during his tenure as Professor of Theoretical Physics at King's College, London (1947-51), would eventually become a classic. In consonance with Pauling, throughout the book Coulson eagerly emphasized the special role played by the alliance of experimental results and chemical intuition in the suggestion of particular mathematical developments.

The presentation of MO and VB theory did not follow their historical order of appearance. MO theory was selected as the first topic because it is 'conceptually the simplest'. 25 Although Valence was undoubtedly a book sympathetic to the MO viewpoint, it did not develop any rhetoric to condemn the VB method. Coulson considered both schemata as approximations whose range of validity had been sufficiently understood 'for us to recognize the folly of trusting to either alone'.26 In the book Coulson acknowledged that resonance was one of the

most powerful ways in which chemical intuition guided one into finding suitable wavefunctions, and that the appeal of the VB method lay in its selection of component wavefunctions that carry pictorial connotation. No analogous comments can be found for the MO approach. However, the book included the new diagrams introduced in the papers referred to above, offering a visual representation of the formation of bonds in water, ethylene and benzene.

In the third part of the book Coulson used both methods indiscriminately, contrasting them in public in a way that Pauling never managed.

Valence was a hit. It sold very well and at a very reasonable price for students. In the three years after its publication 8000 copies were sold; the American market contributed to absorb a considerable fraction of the copies printed, because of the many colleges that adopted this textbook. The same was to happen with the second edition (1961).27

The correspondence between Pauling and Coulson

As soon as his 'little' book Valence appeared, Coulson made sure to send a copy to Pauling.28 In the first days of September 1952 a review of the book by Pauling appeared in Nature. The review was definitely hostile. Pauling felt that both the treatment of the mathematics behind quantum mechanics and the facts of structural chemistry were brief and sketchy. He added: 'It is my opinion that the student (the author says in the preface that the book is intended for chemical students) needs to build up a solid and complete framework of one sort or another, without gaps.' 29According to him none was offered in this textbook. He further accused Coulson of over-enthusiasm for the MO method, which pushed him to make various unsupported claims. The marginalia in Pauling's copy of Valence reveal the criticisms put forward in the review and go even further by claiming:

This is not a book about the broad subject of valence as the chemist understands and uses it but is a book about the quantum-mechanical theory of covalence. There is no mention of oxidation number, the ordinary valence used by the chemist in the consideration of oxidation-reduction reactions, nor is there any general discussion of the valencies of the elements in relation to atomic numbers.30

Coulson immediately replied to Pauling. Two of Pauling's remarks particularly worried him. Not unexpectedly, one concerned Coulson's 'over-enthusiasm for the miolecular] o[rbital] method', the other his treatment of hybridization, to which a whole chapter was dedicated. He concluded his letter asking for help:

I know you are terribly busy. But in view of the interest both here and in America on the matter of hybridization, and the large number of people now working at it, it would be important to get the issue cleared up.31




Predictably, in his reply Pauling conceded that the chapter on 'hybridization' particularly disturbed him because hybridization was a concept he 'discovered (or invented)'32 and was the cornerstone of his resonance theory; he felt that Coulson did not give him proper credit. In fact, in Pauling's copy of Valence all critical comments handwritten in the margins appear in the section on 'Hybridization'. 33 Pauling pointed out that most of the material contained in

34 the chapter was first published in his 1928 paper, in which he hinted at hybridization as a

possible explanation for the tetravalence of carbon, and then, in the first paper of the 'The nature of the chemical bond' series (193 1),35 in which hybridization (not yet named as such) was discussed analytically, together with overlap integrals, the strength of bond orbitals, tetrahedral hybrid orbitals, trigonal-digonal hybrids, and so on.

Despite also being critical on other matters, Pauling was willing to confess that his comments should be taken as personal opinions about questions to which there did not yet seem to be any final answers. And in a subsequent letter, Pauling even explored alternative solutions to their points of contention.36 In his answer to Pauling, Coulson apologized for his unintentional unfairness towards some viewpoints associated with Pauling, confessed that 'I have learnt so much from your work myself as to make me always grateful', and agreed

with Pauling on the importance of the 1931 paper:

I agree with you that the 1931 paper was one of the best things you have ever done; and this is still true even if we discover, as time goes on, that a good many of the details require a certain amount of alteration.37

In Pauling's final reply,38 the angry tone of his former letters disappeared.

Pauling reasserts his point of view

Pauling deemed it so important to reiterate his views on resonance theory that he again made his position public in Perspectives in organic chemistry (1956)39 and later on in the third edition of The nature of the chemical bond (1960).4 More than the question of the artificiality of resonance, to which he had also alluded briefly in his Nobel Prize lecture (1954),41 he

wanted, once and for all, to state as clearly as possible his views on the constitutive character of theory in quantum chemistry. In the preface to the third edition of his well-known textbook, Pauling pointed out that the theory of resonance involves 'the same amounts of idealization and arbitrariness as the classical VB theory'. 42 A whole section was added to

43 discuss this question, bearing the revealing title 'The nature of the theory of resonance'. There, he argued that the objection concerning the artificiality of theoretical entities behind concepts applied equally to resonance theory and to classical structure theory. To abandon the resonance theory was tantamount to abandoning the classical structure theory of organic chemistry. Were chemists willing to do that? According to Pauling, chemists should keep both theories because they were chemical theories and as such possessed 'an essentially empirical (inductive) basis'. 44

Coulson's second edition of Valence and Pauling's The chemical bond

Despite Pauling's insistence on the central role of his structural approach to quantum chemistry, he most probably felt that in Coulson he had found, at long last, a non-antagonistic and understanding interlocutor. In fact, the second edition of Valence (1961) incorporated most of Pauling' s comments and gave more weight to his two earlier papers, and there is more use of resonance.45 But despite Coulson's always conciliatory turn of mind and his declaration of impartiality as to being on the side of the VB method or the MO method, the



266 A. Simoes

fact remains that the latter viewpoint received an impressive boost with Coulson's two editions of Valence. Coulson was also uncharacteristically assertive about the status of resonance. He objected to Pauling's choice of raising resonance into a chemical category, taking resonance as just a heuristic device, an algorithm or a metaphor or simply one pedagogically expedient method (out of various) for understanding quantum chemistry. And, as late as 1970, Coulson could assert that 'resonance is a dirty word'.46 In contrast, Pauling temporarily softened his position. Despite his stubborn lifelong insistence on the unmatchable role of resonance theory, in the abridged version of The nature of the chemical bond, published in 1967, and specifically addressed at students,47 Pauling made a small concession. In the sections 'The hydrogen molecule and the electron bond' and 'The structure of aromatic compounds', he introduced students to the MO approach. Simultaneously, he stripped the textbook of all considerations as to the nature of resonance. However, 13 years later Pauling disparagingly commented, 'it was a tragedy that the writers of elementary textbooks of chemistry decided to discuss the molecular orbital method' .48

CONCLUSION: TWO SCIENTIFIC WORLD VIEWS

When looking at the different editions that The nature of the chemical bond and Valence went through as a result of their authors' ongoing dialogue, one is struck by the evenness of the two discussants: both were charismatic leaders and enthralling teachers, both had humanitarian commitments and they shared the appeal of popularization. Even though they were usually presented as scientists in opposing camps regarding the chemical bond, the fact of the matter was that they were in agreement on many counts. They agreed on the importance of what counts as 'appropriate' and 'effective' training, namely on the importance of quantum mechanics and mathematics for chemistry, but they also agreed on the possibility of avoiding sophisticated mathematics at the introductory teaching level. They agreed on the development of conventions for the moderation of technical jargon, including the recourse to visual representations as substitutes for or complements to advanced mathematics. They were both keen on exploring the changing boundaries between chemistry, physics, mathematics and biology. They were both sensitive to the role of audiences and acknowledged the importance of persuading organic chemists by appealing to traditional chemical modes of thought. However, they could not agree on everything.

They disagreed on the role of a comparative methodology both in doing and in communicating science as well as on the status of theoretical entities behind scientific concepts (such as resonance structures). In fact, behind their divergent views on the use of the comparative method and on the meaning of resonance lay their divergent views on the epistemological foundations of quantum chemistry (and of science), which their dialogical intercourse helped to articulate. Whereas Pauling insisted on a one-sided approach to quantum chemistry and science based on resonance, Coulson excelled at discussing alternative approaches.

The publication of the successive editions of The nature of the chemical bond and its final abridged version was an integral part of an ambitious strategy articulated by its author. Together with his other textbooks and publications, Pauling wished to implement an agenda aimed at nothing less than reforming the science of chemistry from the point of view of quantum chemistry. This agenda also had far-reaching implications in what concerned the status of chemistry within the hierarchy of the sciences. Believing in the 'integration' of the

sciences,49 which he deemed to be achieved through the transfer of tools and methods,




Pauling considered what he called the 'technique of thinking' to be the most important kind of transfer. It is in this respect that he came to view chemistry, and specifically resonance theory, as having a pivotal role within the physical and biological sciences. For Pauling, chemistry, through structural thinking, had a central place, a place formerly held by physics, and science as a whole should be reformed from the standpoint of chemistry.

In contrast, the importance ascribed by Coulson to the application of the comparative method, in research and review papers, in articles on the popularization of science and in textbooks, of which the two editions of Valence are the most representative, made him particularly receptive to exploration of the potential of dialogical reasoning. In a sense his belief in the power of the comparative method reflected his views about quantum chemistry (and generally about science). He was a firm supporter of the view that 'the validity of the scientist's account depends on the degree of interlocking between its elements.' To elaborate on what he meant, he appropriated C. Peirce's cable metaphor, according to which 'the strength of an artificial fiber depends on the degree of cross-linking between the different chains of individual atoms.'50 In an analogous manner, the explanatory success of quantum chemistry (and of science) rested on the degree of interlocking between constitutive elements-its different subcultures with their varying methodological allegiances, its different communities sharing values, commitments and approaches-to such an extent that it was not the relative contribution of each component that mattered, but the way in which the whole was reinforced by the cross-linking and cross-fertilization of all elements.

ACKNOWLEDGEMENTS

This paper is a revised version of a talk delivered at the conference 'The Scientist as Educator and Public Citizen: Linus Pauling and His Era' held at Oregon State University, Corvallis, OR, USA, on 29 and 30 October 2007. I thank meeting participants for their comments, and Cliff Mead for having sent me images of the marginalia found in Pauling' s copy of Coulson' s Valence. I also thank Robert Fox and the two anonymous referees for their criticisms.

Notes

The following abbreviations are used: CP, Coulson Papers, Bodleian Library, Modern

Manuscripts, Oxford; PP, Pauling Papers, Oregon State University Library, Special Collections, Corvallis, OR.

1 Roald Hoffmann, 'Kenichi Fukui (1918-1998)', Nature 391, 750 (1998). 2 Anders Lundgren and Bernadette Bensaude-Vincent, Communicating chemistry. Textbooks and

their audiences 1789-1939 (Science History Publications, Canton, MA, 2000); D. Kaiser (ed.),

Pedagogy and the practice of science. Historical and contemporary perspectives (MIT Press,

Cambridge, MA, 2005); Antonio Garcia Belmar, Jos? R?mon Bertomeu-S?nchez, Manolis

Patiniotis and Anders Lundgren (eds), Textbooks in the scientific periphery (special issue of Science and Education, vol. 15 (7-8), pp. 657-880 (2006)).

3 Mara Beller, Quantum dialogue. The making of a revolution (University of Chicago Press, 1999). In this book the author explores the potential of what she calls a 'dialogical historiography', in

which science is viewed as a result of the ways in which scientists respond to and address each



268 A. Simoes

other, and scientific theorizing is endowed with a multidirectional dialogical nature. In this article

I follow Beller's call for a dialogical historiography while changing from the context of discovery

to the so-called context of pedagogy. 4 T. Shinn and R. Whitley (eds), Expository science: forms and functions of popularization

(Reidel, Dordrecht, 1985). In this paper I take science first and foremost as an act of

communication, be it at the production or at the circulation level, while challenging the

distinction between the production of science and its various contexts of communication, which

involve the publication of textbooks among its many instances. On the circulation of knowledge, see James Secord, 'Knowledge in transit', Isis 95, 654-672 (2004).

5 In the Introduction to the volume Communicating chemistry (Lundgren and Bensaude-Vincent,

op. cit. (note 2)), J. H. Brooke mentions, 'for Hoffman and Lazlo "the conversation reifies the

idea; it selects in the mind of the researcher one possibility of many, it is the first existential act in

science. All the stronger because the talk is free'", on p. 1.

6 Linus Pauling, 'The dynamical model of the chemical bond and its application to the molecule of

benzene', /. Am. Chem. Soc. 48, 1132-1143 (1926); PP, Box 210, LP Notes and Calculations

vol. Ill, 1926-27, 'Work on molecular orbits'.

7 J. H. Van Vleck and A. Sherman, 'Quantum theory of valence', Rev. Mod. Phys. 7, 167-227

(1935). 8 Robert Sanderson Mulliken, 'The electronic structure of polyatomic molecules and valence. VI.

On the method of molecular orbits', /. Chem. Phys. 3, 375-378 (1935), at p. 376.

9 PP, Box 115, W Correspondence, File on Wheland, Letters Pauling to Wheland, 30 October

1936, 13 March, 30 March 1937, 28 July 1937, Letter Wheland to Pauling, 29 November 1936. 10 Linus Pauling, The nature of the chemical bond and the structure of molecules and crystals: an

introduction to modern structural chemistry (Cornell University Press, Ithaca, NY, 1939).

11 Linus Pauling, General chemistry. An introduction to descriptive chemistry and modern chemical

theories (Freeman, San Francisco, 1947) (this publication resulted from a bound book of lecture

notes distributed to students and published as Linus Pauling, General chemistry (California

Institute of Technology, Pasadena, 1941)); Mary Jo Nye, 'From student to teacher: Linus Pauling and the reformulation of the principles of chemistry in the 1930s', in Lundgren and Bensaude

Vincent, op. cit. (note 2), pp. 397-414; Kostas Gavroglu and Ana Sim?es, 'One face or many? The role of textbooks in building the new discipline of quantum chemistry', in Lundgren and

Bensaude-Vincent, op. cit. (note 2), pp. 415-449.

12 Linus Pauling, College chemistry (Freeman, San Francisco, 1950).

13 Pauling, op. cit. (note 10), at p. 12.

14 Ibid., at p. 404.

15 Ibid. 16 Ibid., at p. 407.

17 Ibid., at p. 408.

18 Ibid. 19 Linus Pauling, The nature of the chemical bond and the structure of molecules and crystals: an

introduction to modern structural chemistry, 2nd edn (Cornell University Press, Ithaca, NY,

1940). 20 PP, Box 399. The nature of the chemical bond 1932-1959.

21 C. A. Coulson, Waves (University Mathematical Texts, Edinburgh, 1941); C. A. Coulson,

Electricity (University Mathematical Texts, Edinburgh, 1948); C. A. Coulson, Valence

(Clarendon Press, Oxford, 1952); C. A. Coulson, The shape and structure of molecules (Oxford

Chemistry Series, Clarendon Press, Oxford, 1973).

22 C. A. Coulson, 'Quantum theory of the chemical bond', Proc. R. Soc. Edinb. 61, 115-139 (1941).

See Buhm Soon Park, 'In the context of "pedagogy": teaching strategy and theory change in

chemistry', in Kaiser, op. cit. (note 2), pp. 287-319.




23 C. A. Coulson, 'Representation of simple molecules by molecular orbitals', Q. Rev. Chem. Soc. 1,

144-178 (1947). 24 C. A. Coulson, 'The meaning of resonance in quantum chemistry', Endeavour 6, 42-47 (1947). 25 Coulson, Valence, op. cit. (note 21), at p. 68.

26 Ibid., at p. vi.

27 See discussion in Ana Sim?es, 'Textbooks, popular lectures and sermons: the quantum chemist

Charles Alfred Coulson and the crafting of science', Br. J. Hist. Sei. 37, 299-342 (2004), at

p. 315.

28 CP, Ms Coulson 155, G. 16.3, Letter Coulson to Pauling, 1 August 1951. Nevertheless, on 12 May 1952 Pauling wrote to Coulson that he was still eagerly waiting to receive a copy of the book.

29 Linus Pauling, 'Quantum mechanics of valence', Nature 170, 384-385 (1952), at p. 384.

30 PP. Pauling's copy of Valence. Marginalia. Handwritten comments in the blank endpage of the

book.

31 CP, Ms Coulson 155, G.16.3, Letter Coulson to Pauling, 8 September 1952.

32 Ibid., Letter Pauling to Coulson, 25 September 1952. 33 PP. Pauling's copy of Valence. Marginalia. Section on 'Hybridization', pp. 191, 208, 209

and 212.

34 Linus Pauling, 'The shared-electron chemical bond', Proc. Nati Acad. Sei. 14, 359-362 (1928). 35 Linus Pauling, 'The nature of the chemical bond. Application of results obtained from the

quantum mechanics and from a theory of paramagnetic susceptibility to the structure of

molecules', J. Am. Chem. Soc. 53, 1367-1400 (1931). 36 CP, Ms Coulson 155, G.16.3, Letter Pauling to Coulson, 4 November 1952.

37 Ibid., Letter Coulson to Pauling, 14 July 1953.

38 Ibid., Letter Pauling to Coulson, 12 September 1953.

39 L. Pauling, 'The nature of the theory of resonance', in Perspectives in organic chemistry, dedicated to Sir Robert Robinson (ed. Sir Alexander Todd), pp. 1-8 (Interscience, New York,

1956). 40 L. Pauling, The nature of the chemical bond and the structure of molecules and crystals. An

introduction to modern structural chemistry, 3rd edn (Cornell University Press, Ithaca, NY,

1960). 41 L. Pauling, 'Modern structural chemistry. Nobel lecture, December 11, 1954', in Nobel lectures

in chemistry 1942-1962, pp. 134-148 (Elsevier, Amsterdam, 1964). 42 Pauling, op. cit. (note 40), at p. vii.

43 L. Pauling, 'The nature of the theory of resonance', in Pauling, op. cit. (note 40), pp. 215-220.

44 Ibid., at pp. 219-220.

45 C. A. Coulson, Valence (Oxford University Press, 1961). 46 C. A. Coulson, 'Recent developments in valence theory', in Fifty years of valence theory (Pure

Appl. Chem. 24, 257-287 (1970)), at p. 258.

47 Linus Pauling, preface to The chemical bond (Cornell University Press, Ithaca, NY, 1967). 48 Linus Pauling, 'Prospects and retrospects in chemical education', /. Chem. Educ. 57, 38-40

(1980). 49 Linus Pauling, 'The place of chemistry in the integration of the sciences', Main Curr. Mod.

Thought 1, 108-111 (1950); republished in Barbara Marinacci (ed.), Linus Pauling in his own

words, pp. 107-111 (Simon & Schuster, New York, 1995).

50 C. A. Coulson, Christianity in an age of science [Riddell Memorial Lectures] (Oxford University Press, 1953), at p. 37.



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