Stamping Out Misconceptions J. D. Bradley and M. Brand University of the Witwatersrand, Johannesburg, South Africa One of the essential characteristics of chemistry is the constant interplay between the macroscopic and microscopic levels of thought and discussion (I). This interplay process ( 2 ) - m e of the most difficult general intellectual skills for beginners to develop-is crucial for success in chemistry. Yet little formal attention is given to this development, and carelessness in our own use of language compounds the difficulty (3). The result is a pervasive "error factor" (4) that contributes to many student difficulties in areas such as the mole concept and stoichiometry (5). A Simple, New Tool
T o confront directly student difficulties in this area, we have introduced the use of rubber hand-stamns to eenerate molecular pictures. These scamps (:an be prepared with shapes of atoms and molecules at little cost bv small. local orint shoos. The rubber hand-stamps consist ofbntlind shapes of atoms and diatomic and triatomic molecules of assorted sizes and shapes. With the aid of these stamps and an ink pad, teachers can create pictures for overhead proiedion and for worksheets (6). Even better, students can use them toillustrate their own conceptions of the microscopic situation that corresponds to a macroscopic one. In such an active environment i d uninhibited by the need for artistic skills, many deeply-buried misconceptions may come to light and hence can he corrected
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1he stamp-generated pictures are useful in discussions of the macroscopic/microscopic meanings of terms such as element, compound, mixture, homogeneous, and heterogeneous, and in discriminating types of chemical formulas (empirical,
molecular, projection, structural) (Fig. 1).Another important use is in development of the distinction between intermolecular and intramolecular forces (chemical bonds). For this latter purpose, the use of "realistic" molecular outlines, (as o.~.o o s e dto ball-and-stick or touchine circles). . . is imoortant. Chemical reaction concepts (e.g., stoichiometry, extent, and rate) are also illuminated with these tools. Short seauences of pictures are readily created to represent instantaneous microscopic snapshots a t various times (Fig. 2). Scope and Limitations Of necessity, printed pictures are static and two-dimensional, whereas the reality is dynamic and three-dimensiunal. Students need freqnentl; to be reminded of these limitations. Our stamps represent molecules with only two or three atoms hecame of the difficulty of portraying more complex molecules effectively in two dimensions. However, given the purpose of the stamps, this simplicity of the mo1ec;lar shapes is-not an important limitation. Molecular models have often been emnloved in teachine and learning strategies designed to tackle many of the same conceotual orohlems (d). Models have the advantaer of beine three:dimehsional, hut they also have l i m i t a t i o n s r ~ h ecan ~ rarely he viewed adeauatel~in larae classes (9). Moreover. while space-filling mddels &e exceflent for re&esenting in: dividual molecules they are less satisfactow in communicatine the crucial interplay between the macrosco$c and micros cop^ levels. For this puroose . . there are ereat advantaees in reoresenting substantial numbers of atoms and molecules together. This is less readily achieved with molecular morlels than with pictures.
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Conclusion Two-dimensional pictures of microscopic situations have been used by others (6). They also appear in some general chemistry textbooks (10). Our stamps are an improvement in that teachers and students can rapidly create pictures representing the microscopic state that can he linked to macroscopic descriptions for active conceotual exoloration (11).with this toocone of the most i m p o r t k t hasiiintellectual skills of chemistry mav be more readilv- acouired. . and many misconceptions ;an be stamped out. Figwe 1. A. A heterogenof two liquids.
Time: 0 hr
mixture oftwo liquids. B.A homogeneousminure Literature Cited (11 Y-, B.."NuffddChmisUy: InVadunionand Guide:'LongmansiPen~, London, ISM, p. 5. (21 Sd1ey.N. .J,.Edu.Chrm., 18,171,(1981). (3) Selley. N. J.,Educ. Chem., IS, 144, (19781. (41 Pickthorne,B.,Imtruct.Sci, 11,281,(19S3). (51 CerveUati,R,Monhuuhi, A., Perubini. D., GraneUini-Tomini, N..and Pm"Bslandi, 0.. J. CHEM. EDUC.,59, 852, (1982): Dierka, W., Europ J. Sci.Educ. 3, 145 114e11 ,.--.,. (61 Cf James, H. L a n d N e h , S. L., J.C ~ MEouc., . 58,477,119811. (11 (a)Nusahaum,J.,andNovick,S.,Imtmet.Sei.,ll.l83,(19S2).(b)Hew8on,P. W.,S. A. J. Sli., 76,397 (19801. (8) (a) Barke, H. D.. Chim. Di&ct.,7,57.(19811.(bl Omgraonyan,A."ThreeCognitive Time: 1 hr
Time: 10 hr
Figure 2. Represemation of a gaseous reaction minure at times 0. 1, and 10 h. The balanced chemical equation is AS + B = A2B.Th8 reaction reaches equilibrium wilhln 1 h. B atoms are in noichiomehic excess. 318
Journal of Chemical Education
Skills in Chemistry and Their Application to Stoiehi~metry.~ unpublished PLD. d i s s esum. r t ~ '"~ university ~ of CaXfmnia,Bcrkeley. 1977. lcl Gmdsrem. ' ' m. P. and HOW*, A " J. Cm.EDUC.,55.171,(1978). (9) ~ l i d ' d ' ~ ~ f m dare e l sVUY helofi "
1978. (111 la1 Kean,E.,J. C m . E~uc..69.957,(19821.lbl H e m , J. D., J. CHBM. EDUC.,SS, 165, (19781.
