in this issue Taking a Closer Look Taking a closer look a t assumptions, concepts, rules, and information that have become part of our knowledge of a subject can often yield surprising results. For many reasons, this supposed knowledge can be inaccurate: through .. oversimplification, misapplication of principles, w, evcn, the steady accumulation of new scientific data and insight over time. It never hurts to examine the things we teach to see if time has changed the "truth" or if our attempts to simplify concepts for beginners have led to misrepresentation. Several articles in this issue share the common thread of takine a second look a t tooics as diverse a s LeChatelier's principle to the nuclear powpr indutry. We have been usine L~Chatelier'sonnciole for over 100 years to predict the okcome when a iystek at equilibrium is stressed; however, there has been an ongoing controversy about its usefulness. While not taking sides in the discussion of the principle's appropriateness, Yang (page 94) examines a system where its application requires more subtle reasoning than usual to produce the wrred prediction and explanation. The effect of decreasing pressure on a Nz04-NOz equilibrium at constant temperature is often predicted to be an increase in the amount of brown NOz linked with a deepening of the color in the container. However, Yang points out that this simple prediction does not take into account the effect of the concomitant volume change, which actually produces the opposite visual result. Since many textbooks use this as an example illustrating LeChatelier's principle, teachers should look at their presentation of the "facts" about this system. There are many pitfalls for those introducing new concepts to students. Physical phenomena cannot always be explained by one concept or rule, but students must learn these concepts and rules one at a time. The result is that sometimes a relationship, such as that between bonding and melting points, is explained similarly for all compounds. Lingafelter (page 98) illustrates the problems that arise when covalency is automatically linked to low are assumed to be comelting points: the MXA .compounds . valentvbecause of their low melting points, and this is stated explicitly or implicitly in many texts. A closer lwk reveals that the true explanation of the low melting points is more complex, involving the crystal structure of the solid. He summarizes the imoortance of the relative ionic sizes and coordination numbers in determining the behavior of this class of compounds. Similarly, a n attempt at simplification of the description of a wmplex biochemical reaction leads to erroneous infor-
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Journal of Chemical Education
mation on the formation of peptide bonds. Stojanoski and Zdravkovski show, in this month's Textbook Forum (page 134). that the thermodvnamic calculations do not s u ~ ~ o r t the Simple equations often given and that a closer loik a t how peptides are prepared in the laboratory and in organisms shows the need for a promoting agent. Another area that needs frequent reexamination is nomenclature, both for chemical compounds and physical phenomena. As our knowledge becomes wider and our theory more detailed, terminology can become obsolete or inadequate. Sometimes new terms must be coined; sometimes definitions must be rewritten. Reinke, Dehne, and Hans (page 101) take a closer look a t the problems involved in defining allotropes and polymorphs, trying to sort out the properties associated with polymorphism and offering their modified definition. Even when terms are carefully defmed and have been in use a long time, we can thoughtlessly use them in an unexamined way. Peckham and McNaught (page 103) take a closer look a t how the terms "heat", "work", and "energy" are used by teachers and students. Because they have "everyday" meanings as well as precise scientific ones, they are subiect to loose usage. point out that "Heat and work are Not 'Forms of Enerw' " and Drowse an analow that helm teachers explain the difference to students. Teachers can benefit from taking a closer look a t some areas of chemical inquiry simply~becausethey are currentlv so relevant to our lives that much research is underway and students will want the latest views and information. Two such newsworthy topics are acid rain and nuclear energy Baedecker and Reddy (page 104) present the resufii of their recent work ex&&ng the &remental imoact of acidic deposition on carbonate stone surAn example faces relative to natural ~eathering~rocesses. of how this sort of process can effect public monuments is shown on this month's cover. Certainly few scientific topics generate a s much impassioned discussion in the media as nuclear power generators. Miller (page 109)examines the advantages and disadvantages of nuclear power that have been revealed since the industry began in the 1950's and shows how modifications must be made so that the advantages can outweigh disadvantages. The article provides a resource on reactor desien. - . economic considerations. and safetv concerns that should help teachers from the se&ndary s&ool level on up to answer student questions and put the public discussion on a rational basis.
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