edited by JOHNW. MOORE
Werner and Jorgensen: Presentincl History with a Computer David M. Whisnant Wofford College, Spartanburg, SC 29302 Except for the use of historical anecdotes, not many of us structure of N H X l now? How do the concents of ionic and incorporate the history of chemistry in our courses (1). This covalent bundink h d p us descrilw U'erner'~k c t n r r s ? is often a matter of time. Episodes in chemistry usually are T o hrlr, intenrate the i~mulationwith the course material. complex, requiring more time for their historical research t h e stu.den& p r e p a r e t w o m e t a l a m m i n e s , CO: than most teachers of standard chemistry courses have [C03(NH3)4]N03and C O [ ( N H ~ ) ~ ( H ~ O )in] Cone I ~ of , the regavailable (2). If a teacher can do the research, the problem of ular first-semester laboratories (13). Questions in the labwhere to fit history into lectures remains. If we want to oratory handout relate the structures of the two metal amspend time on history, what regular material do we leave mines to the theories of Werner and JBrgensen. The out? background from the simulation also is helpful when disA student in mv general chemistrv class recentlv worked cussing coordination compounds in the second semester of on an honors project (3) analyzingthe ~ e r n e r ~ 3 r ~ e n s e n the course. controversy from the standpoint of Kuhn's descriotion of Iluriny the l l t h ( e n r ~ ~ rrhemistrywaiina v, muddled state scientific change (4). This significant episode in the history with uncertai~~ or inaccur~traturnic and molecular weirbts of coordination chemistry is well documented (5-12), espeand fuzzy ideas about chemical combination (atoms a n d cially in the books and articles by Kauffman, and thus was a molecules of an element were not always distinguished). To good one for nonhistorians to tackle. The project was intersimolifv . .the .oroeram modern atomic and molecular weiehts " esting: Kuhn's description does fit some of the changes that are used, along with molecular formulas consistent with took place during the 19th century, with an interesting difthese weights. The chemists introduced in the oroeram . u also ference or two, and studying chemists along with chemistry are limiteb to a few major figures. The program is written in humanized the subject. The project's success led me to write the same spirit as other topics, such as thermodynamics or a computer simulation covering this controversy. The simuchemical kinetics, presented in general chemistry-the inlation is designed to introduce general chemistry students to troduction of major points, with accuracy if not completethe Drocess of science-how theories develoo. ness, leaving details to later courses. . . how chanee occurs, and hmv scientists hrhme. It is verv graphici-orientPart 1: Molecular Structure t:d, fcnt~~ring picture, d'nll the chemists involved and allowing the cmsrruction of molecular structures on the graphics Werner's structures for the metal ammines were truly w e e n . The simulation i i assigned durinr the last "art nt'thr revolutionary, hut may not appear so to those who have nb first semester, after we have covered bonding and Lewis feeling for the "normal science" of the time. The simulation structures, but before we have encountered the chemistry of first looks a t the develooment of the conceots of valence and coordination compounds. The students work on the exercise molecular structure u p to around 1870 (i5-22). Bailar has independently over a period of two to three weeks. The written, "the history of chemistry in the nineteenth century simulation is divided into two sections. Both sections are is largely an account of the growth of our knowledge of accompanied by handouts which are integral parts of the molecular structure" (12). It is h o ~ e dthat the molecular exercise. structure section gives students an adequate background for The handouts contain short descriptions of Kuhn's thethe metal ammine controversv. Beginning with the theorv of ory, of the state of chemistry during the time of the simulaDualism, the simulation moves to-the radical theory o i o r tion, and of the major participants. They end with a number ganic compounds, discovers the breakdown of dualistic conof questions designed to guide the students' thoughts about cepts due to substitution, and finally notes the rise of the the process of change in science and about the connections valence concept and unitary theories of compounds. I t ends between 19th-century ideas and modern ideas about chemiswith the recognition by Couper and Kekul6 that carbon try. How well does ~ " h n ' spicture describe the change from atoms are tetravalent and can link together in chains. a dualistic to a unitary paradigm in the mid-19th century? The molecular structure section of the simulation is subdiHow does it fit the change in ideas about the structures of vided into three parts, corresponding to the dualistic theory the metal ammines? Considering their responses to change, of Berzelius, the radical theory, and the valence concept. does Berzelius or JBrgensen serve as a better model for an The students are introduced to each theory by one of the ideal scientist? What theory, in a sense, is revived by chemists involved in its development. Then the students are KekulCt's "molecular comnounds" such as P C h" . CI*? What asked to choose structures for different compounds in the does this suggest about the picture of scientific progress as a light of the new theory. For example, in the first part, Berzeone-way path with no blind alleys or wrong turns along the lius introduces his theory of dualism, followed by two way? JBrgensen's chain structures required pentavalent niscreens of information about the theory. A picture of Berzetrogen, patterned after NH4C1. How do we describe the lius, drawn with the Graphics Magician utility package (23) ~~
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to resemble his portrait, is included in the introduction. The students then are asked to choose structures for comnounds like CaCO? using this theory, a task that is easy for minerals hut difficult for the oreanic comnounds encountered in subsequent questions. ~ h & difficuities e lead to the next part of the molecular structure section-the radical theorv, .. still dualistic, but hetter able to deal with organics. You mav note that the students are not asked to discover the theories, which would be difficult. They are required to work with the theories and are encouraged to recognize some of the problems that developed as new compounds were prepared. In the handouts and the pictures on the screen, they meet a few of the major figures in chemistry during the 19th century: Berzelius, Dumas, Wohler, Liehig, Gerhardt, Frankland, and KekulB. They discover how scientists sometimes react when a scientific revolution threatens their ideas.~,for the chanee from a dualistic to a unitarv concent of chemical coml)inntina has many of the characteristics of the rcvolut~msdescribed bv Kuhn Iii. . . Thev . gain some feelinrfor the mainstream of chemical thought in this century and, it is honed. structures for the . . can see how the Jdraensen , metal ammines make sense within this context. ~~~~
Part 2: The Metal Ammlnes The second part of the simulation begins in the 1870'9, a period in which organic chemistry was thriving hut in which inorganic chemistry was still in a chaotic state (15). In 1869 Blomstrand introduced his chain theory for the metal ammines, hased on chains of ammonia molecules analogous to the chains of methylene groups that were so successful in describing hydrocarbons. This theory was developed by J$rgensen in the following years, leading to structures such as that for luteocohalt chloride, Co[(NH&]Cb,
In 1893, Alfred Werner proposed his octahedral structures, which now appear in all general chemistry texts, but which, at the time, represented a sharp break with the classical theory of valency and structure (7).The ensuing controversy between Werner and J$rgensen is an excellent example of scientific competition. The beginning of this part of the simulation introduces the two theories describing the structures of the metal ammines. First, the students build chain structures on the screen and discover the difference between reactive and unreactive chlorine by precipitation with silver nitrate. Werner then introduces himself and explains his theory, following which the students formulate octahedral structures. An attempt is made here to show a dialogue between the two protagonists: after Werner has introduced his theory, J$rgensen responds with his criticisms, and then Werner responds to these comments. This dialogue is maintained throuehout the rest of the nrogram. When one chemist makesan assertion, the otherkesponds. After the two theories have been introduced, the students can test them by experimenting with eight octahedral cobalt(II1) ammines. They can predict the number of reactive (ionizable) chlorine atoms on the ammines, measure the conductances of the ammines, and learn about the number of isomers for the ammines. They find that both theories agree on most of the conductance predictions, hut that two o? the predictions favor Werner's structures. On the other hand, neither theory makes the correct predictions for two other compounds, which JBrgensen takes as evidence that the conductance method is not reliable. Werner responds that the failures are due to reactions with water. When they look at isomers, the students find that Werner and J$rgen-
sen do not always agree on the number of isomers that a compound should have. For instance. Werner's theorv, nre. dicta cis and trans isomers for [COCI!(NH~)~ICI, bur Jprgensen's dues not. Whrn thesrudents first test the theories. onl\. one isomer, the praseo (trans) form, has been prepared: ~ h " e apparent nonexistence of the violeo (cis) isomer indicates to JBrgensen that Werner's theory is not valid. As they work through this part of the simulation, the students may ask Werner. or JBrgensen for advice (their pictures appear when the advice is given). Along with making the simulation more personal, this feature reduces confusion and gives the students some guidance, should it he needed. Whenever they wish, the students can throw their support behind one theory or the other. In order to finish they must support a theory and show, by their responses to a few questions, that their support is based on more than guesswork. Once this support has been given, Werner announces, as he did in 1907, that he has prepared the violeo isomer. At this point JCgensen eraciouslv concedes that Werner's views are valid; a i d the s&lation ends. The simulation ends the treatment of the Wernerddraensen controversy at this point, although more work remained to he done. Evidence from "isomer counting" among compounds such as [CoC12(NH3)a]CIand C O C ~ ~ ( Nwas H ~not )~ sufficient to prove conclusively the octahedral configuration of cohalt(II1). The resolution into optical isomers of coordination compounds containing chelate groups, which Werner accomplished in the period between 1911 and 1914, unequivocally established the existence of the octahedral configuration (24). Concluding Remarks
This is a lone simulation. taking from 2 to 3 hours for most people to fi&. ~ e s p o n s e tso 3 questionnaire distributed to n class 01'30 studrnti indicated that thev like it. 'I'hr nrerner rating given the simulation was 8 on a scale of 10, and every student thought that i t should be used next year. Judging from comments on the questionnaire, this was not an easy project. T o one student, it was "long and hard to understand", hut, to another, "the challenge involved in supporting a theorv was a good time." Most students were able to understand the ma& ideas in the simulstion, hut only a few grasprd the more subtle points. All of the students answered the kasier questions in t h e handouts. Most answered the more difficult ones about relationships withmodern chemistry and Kuhn's theories, although not always completely. A few of the better students gave very well-thought-out and detailed answers, sometimes covering the front and hack of the page. Judging from the time spent on the computers and the answers to the auestions. it seems that the students took the exercise seriously-a potential problem when history is included in a standard chemistry course ( I ) . I think the simulation is worthwhile and I plan to use it aeain. It introduces students to the historv of an interestine period in chemistry. It personalizes one part of the courseas one student wrote. "I felt as if I were interactine with Werner and ~yir~ense;while I debated over which iheory was better." It offers another ontion to those of us who would like to include history in our cburses hut who have not been able to do so in lecture. This DOS 3.3 simulation is written for a 128K Apple IIe or IIc with one disk drive. A high-speed disk utility (25) would hr useful tocut down the t i m ~ e s p ~ in n tl m d i n ~ p&rnms and picture.;. Thssim~llntionumil he a\.ailahle from Project SER,\I'Hlhl. Professor John .\loorr. Denartnient of Chemi3tr\.. Eastern Michigan University, ~ p s i l a n t iMI , 48197.
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Acknowledgment I would like to thank Dan Hank and James Keller, from our philosophy department and Rick Swiger for stimulating discussions during the project that led up to this program. Volume 64
Number 8 August 1987
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Llterature Cited I. Hermn. J. D.et a1.J. ChemEduc. 1977.54. 15. 2. Cnldwhite, H. J. Charn.Edue. 1915.52.645. 3. Swige.. R.,unpublished d a b . 4. ~ u h n . S. ~ . he structure oisrienrifie Reuoluriona, 2nd ed.: univenity of chicago. Chicago, 1970. 5. Kauffman. C. 8..Ed. Clossie~in Coordinntion Chemistry: Part 1: Dover: Near York, 1966. 6. Kauffman. G. B.. Ed. Clossica in Coordination Chemistry Part $ Dover: New York.
1956:Chapter 2. 13. Schlesinger,G. Inorg. Syn. 1960.6.173.
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14. Cohen,P.S.In WemarC~ntenniol,Kauffman,G.B.,Ed.;AmericsnChemicalSociety: WeshingtonDC. 1967:Chapter 3. 15. Ihda, A. J. The Deuelapmeni oiModsmChrrnisfry; Dover: NevYork, 1964; Chapters 4-8. 16. Bmfey, 0.T. From Vital Farm to Strulurol Foimulos: American Chemical Society: Washington DC, 1975. 17. Palmer, W. G. A History 01 the Concept of Volency to 1930; Cambridge Univenity: Cambridge, 1965. 18. Russell. C. A. The Mstory oi Valeney: Leicester University: Leicester, 1971. 19. Loicester. H.M. The Historical Background oiChernisfry; Wiley: New York, 1956. 20. Findlay, A. A Hundred Ymrs of Chemistry, 3rd ed.: Duckworth: London. 1965. 21. Benfey.0.T. Ed. Claasicr in the Theoryof Chemical Combinalian; Krieger: Malabar, FL, 1981. 22. Mack1e.H.J. Chem.Educ. 1954.31.618. 23. POLARWARENeneuin Software.260OKeslinaer Rd.,PO Box 311,Geneva. IL60134.
&I, R ~ ~ &0 . . B.. ~d.;A&ri& chemieai~oeiety:washing&, DC, 1975: pp 126-142. 25. An example is PmntoDOS, Beagle Bms, 4315 Sierravista, San Diego. CA 92103.
