DOCUMENT RESUME ED 247 134 SE 044 730" , AUTHOR Kooser,. Robert G.; Factor, Lance TITLE Cubes, Eights, and Dots: AStudent's Guide to the Octet Rule and Its History. SPONS AGENCY National Endowment for the Humanities(NFAH), Washington, D.C.; National ScienceFoundation, and Values in Science and Washington, DC. Ethics7 Technology Program. PUB DATE Jun 83 NOTE 25p. PUB TYPE Guides ClassrooMNUse Materials (For Learner). (051) EDRS PRICE MF01/PC01. Plus Postage. DESCRIPTORS *Chemical Bonding; *Chemistry; CollegeScience; Higher Education; High Schools;Science Education; *Science History; *Secondary SchoolScience IDENTIFIERS *Octet Rule ABSTRACT This exercise is designed to correctthe impression of many students thatscientific facts are unchanging. Every scientific fact has a history andits history shapes the formwhich the fact takes in a textbook.Thus, the history of the octetrule is traced to show that scientificknowledge is not a cast iron setof facts but rather a fluid bodyof information shaped bythe people who The exercise consists of areading and use it for specific purposes. answered by a set of discussionquestions.. The questions can be students or could form thebasis for a class discussionabout the issues raised. It is suggestedthat the exercise be used afterthe lesson on the octet rule andLewis dot structures. (JN) *********************************************************************** the best that can be made * * Reproductions supplied by EDRS are * * from the original document. *********************************************************************** CUBES,EIGHTS AND DOTS A Student's Guide to the OctetRule and its History U.S. DEPARTMENT OF EDUCATION NATIONAL INSTITUTE OF EDUCATION EDUCATIONAL RESOURCES INFORMATION CENTER (ERIC' This document has been reproducedas received horn the person or organization originating it Minor changes have been made to improve reproduetion quality. Robert G. Kooser Points of view or opinions stated in this docu Lance Factor meet do not necessarily representofficial NIE Positron or policy Khox College Galesburg,IL not dare to tell our students that Dalton's We do wasmade magnificent construction of the atomic theory by his deliberate adjustmentof certain' experimental possible impugn the results to fit his theory, since thiswould alledged empirical foundation of his atomic theory. ...In a° of not too long ago, a scientificcolleague argued debate teachers of science that it was for this very reason that well advised.not to use He also would be example" for our askedwhether. it would be an "edifyin students to ltarn that Pauli discovered one of the most (the exclusion important principles of modern physics Copenhagen: principle) while relaxing at a "girls show" in be, cfcourse, that we mustdecide whether The answer what our students to become perfect models of - we wish And)scientists to be, or textbook writers envisage science whether we wish them to beDaltons or Paulis." Science" in I. Bernard Cohen,"Historyand the Philosopher of The Structure of ScientificTheories,edited by Frederick Suppe(Univ. of IllinoisPress,1974)p.341. "PERMISSION TO REPRODUCE THIS r' MATERIAL HAS BEEN GRANTED BY Anta TO THE EDUCATIONAL RESOURCES INFORMATION CENTER (ERIC)." ACKNOWLEDGEMENTS help of our would like to acknowledge the We assistance in preparingthe colleague, Dr. Henry Rouser, for case study. Dr. Derek Davenport of evaluation for this finding University was most-helpfulin assisting us in Purdue Mr. Nick backgroundmaterial for the work. appropriate of Knox College of the AudioVisual Department Dvoracek thiswork and its prepared the figures. Production of possible by a grantfrom the National distribution was made and Ethics and Values in Science Science Foundation's for the program and the National Endowment Technology and Human Values. Humanities' ProgramofScience, Technology findings conclusions or recommendations Any opinions, and do not herein are those of the authors expressed the National Science necessarily reflect the views of Foundation or the NationalEndowment for theHumanities. alP Knox4 College 1983 <4, . A NOTE TO TEACHERS Thiswork is designed to introduce students in an chemistry class to a number of featuresabout introductory mentioned in a chemistry scientific knowledge that are seldom purpose is several fold:"kfirst of all we are class. Our students that seeking to correct the impression of many facts are unchanging. Every scientific fact has a scientific form which the fact takes history and its history shapes the In this case, the octetrule and the shared in a textbook. atomic bondwere born in association with U specific ,pair used today, model,the cubiCal atom, and the notation, still with the theory had a specificmeaning in terms of connected octet rule that model. Here we trace the evoluti-bn of the shared pair bond to its present textbook form. and the enter into Secondly, this study shows how personalities can process and" change the course ofscientific the scientific Moreover, it The role of models is demonstrated. thinking. preconceptions can alter the way can be seen that theoretical does( not about scientific--problems. Science one thinks After-working alwayswork from" the data to the theory. study, we hope thestudent will have a clearer' through this about viewof the way science worksand a less naive attitude the nature of scientificknowledge. that thi work would be .used afterthe We envision There are on the octet ruleand ewis dot structures. lestom and 'hese discussion questionswhich et at.our major points answered by the students and couldform the basis ,could be the issues the study for a periodof class discussion about raises. -CUBES, EIGHTS AND DOTS The purpose of this paperis in some ways simpleand read some ways complex.In a 'cal chemistry textbook you 4 1 about chemical facts 17 em solving strategies;little is said about where t s come from or.how. Ahey evolved into the form which you the textbook.. The impression one gets is thatthe facts no history and thatthey orginially took the form which you seein the-textbook. This. is seldom the case because46st of the facts that you learn to have a rich history, andt4 have ungone a long evolution reach their present form. This form is generally easyto understand, remember; andsimple for the beginningstudent to They have use. Such facts are the samein all textbooks. been reshaped by the chemistsand teachers to becometools of instruction and calculation. Borrowinia phrase which is sometimes used by philosphersof sciencel'cwe will callthese kinds of facts standardizedfacts. Our purpose'-hele is to take one such standardfact, the octet rule, andexamine i.ts history. We wish to demonstratethat scientific knowledge it not a cast ironset of facts but, rather afluid body of information shapedby the people' wh6 use itfor specific purposes. et If you took up 'octetrule'in your textbook, youwill probably find a short °statementattributing the rule to the American chemist, G.N. Lewis,and then you /ill find a :statement of the rule which goessomething like this: "Atoms :by sharing electrons to form anelectron pair bond can 2 acquire a stable noble-gasstructure."(Masterton et.al.,ChemicalPrinciples.AlternateEdition,2nd noble-gas structure ed.,p.185). Remember that .the stable involves a valenceconfiguration ofeight electrons. introduced to Following the statementof the rule, YOU are valence electrons in the dot formularepresentation for the structures for atoms and instructedin how to write dot directions to ensure molecules, usually byfollowing a set of examples are that the correct formulais written. Next some bonding structure in given in the use ofthe rules to predict molecules, and then you areinvited to practicewriting given over to structures yourself.Some space is usually indication of exceptions to the rulewhich are taken as an In what follows, we the lack of itsvalidity in every case. will examine the historyof the octet rule andtraceits evolution in the work ofG.N.Lewis, the chemist whois most often identified as itsoriginator. While Lewis firstpublished the octet rulein 1916 (Lewis,1916), its origins goback much further. They are firmly rooted in Lewis's veryoriginal (and in our minds A page unusual) notion of thestructure of the cubicalatom. Figure 1. Here he from his notebooks,dated 1902, is shown,in of the conceived of the atomsof the first three rows periodic chart .AS cubeswith the electronsoccupying Li places in the cornersof the cube. Thus the structure of of the cube, is shown with just oneelectron.in the corner vacant; the innner electrons, as the other positions-being in smaller cubes Lewis speculated, werethought to reside , 6 3 Lewis thought inside the 'valencecube'.(Note, at the time- electrons; the that helium had acompleted cube of eight had not yet been evidence showing Hehad only two electrons eight in the discovered). The special role of 1.4.2r÷ I showing his early, Figure 1. A page fromLewis's 1902 notebook cubical atoms. discoveries, but theory of molecules wasnot one of Lewis's explaining it in terms ofthe electronicstructure of atoms in cubical form was hisnovel idea. As the notebook shows, Lewis was trying toexplain the bonding inionic compounds. complete the octet Thus, for NaC1 sodiumloses an electron_to This leaves both, theNa of the-chlorine atom(see Figure 1.). stable and Cl with completedoctets, and hence in a configuration. 4 4 you -While the cubical atom mayseem naive.to you, read ifyour textbook orhear in mu-s remember that what you chemists and classi s thetesult of the work of many 1902.