In the Classroom
A Framework for Presenting the Modern Atom James J. Leary* and Tadd C. Kippeny Department of Chemistry, James Madison University, Harrisonburg, VA 22807; *
[email protected] Features, papers, editorials, and letters in this Journal provide prima facie evidence that the content of introductory courses in chemistry at the college/university level is being extensively scrutinized and debated. As the body of knowledge associated with chemistry grows, decisions must be made about the relative worth of specific material. Such scrutiny is, and will continue to be, critical to the vitality of the discipline. The abundance of material that might be treated in these courses is a strength of the discipline, not a weakness. Although the topics “deemed essential” are likely to change with time, it is reasonable to expect that introductory chemistry courses will cover what Gillespie calls “The Great Ideas of Chemistry” (1), at least throughout the foreseeable future. It is imperative that the pedagogy of college/university education continue to be based on the Great Ideas, and not fall into the trap of reducing education at this level to a mechanistic system of “learning objectives”. As technological developments contribute to the overall challenge of educating, it is essential that faculty members continue to be afforded great flexibility under the banner of academic freedom. Guidance regarding major topics or Great Ideas can be invaluable, but faculty must be granted considerable leeway because an essential part of our responsibility as educators is to help students develop as individuals. Students must be challenged to think critically, if eventually they are to be entrusted with the responsibility for societal and scientific advancement. To achieve this end, all aspects of major chemical accomplishments should be discussed. It is within the Great Ideas context that we present a general framework for the presentation of material related to experimental and theoretical developments that we call the “modern atom”.
and theoretical developments in more detail. Of course, individual faculty members are encouraged to add to the chart at their own discretion depending upon their specific goals. Further Considerations Several additional points should be considered. First, the flow in Figure 1 indicates that there are indeed interconnections, and that our understanding of the atom is not the result of a set of important but unrelated experiments. The dates show the historical context of the work; in many cases these dates are approximate and reflect major international presentations or publications. The chronology makes it easy to see that it would not have been possible for (i) Millikan to calculate the mass of the electron, if Thomson had not already determined the charge-to-mass ratio, (ii) Rutherford to bombard a gold foil with α-particles, if these particles had not previously been isolated and identified, (iii) Chadwick to set out to verify the existence of neutrons, if Aston had not previously discovered isotopes. These examples also illustrate the impact of technology on this scientific progression. In each case new instrumentation paved the way for further advancement. Modern chemical instrumentation makes it
The Framework In 1982 Haendler published a paper in this Journal that included a flow chart related to major contributions to the Bohr atom (2). Figure 1 is an expansion of Haendler’s chart that includes many of the major contributions to our current view of the atom. Contributions by some very well known scientists are not included (e.g., Born, Rydberg, Roentgen, Dirac, Hertz, Moseley, Pauling) because Figure 1 was designed as a one-page internally consistent framework. One might claim that there is little that is new or novel about this presentation because similar developments can be found in one or more chapters of most introductory chemistry texts. However, a single-page summary makes it easier to see a number of things that can be missed in a text-based presentation. The flow chart also provides a systematic overview that is independent of the level of presentation. For example, variants of this chart have been used in four different entry-level courses at James Madison U. In courses designed to meet the liberal education needs of a broad cross-section of the student body, the chemistry is presented with a heavy emphasis on the historical, political, and social context. In contrast, an accelerated section for chemistry majors treats the empirical
Figure 1. The Modern Atom: a flow chart of major theoretical and experimental contributions (who, what, and when).
JChemEd.chem.wisc.edu • Vol. 76 No. 9 September 1999 • Journal of Chemical Education
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In the Classroom
possible to more rapidly analyze ever smaller quantities of material with greater sensitivity, thereby significantly influencing scientific developments in fields ranging from molecular biology to environmental monitoring. It is always nice, class time permitting, to discuss contemporary examples that illustrate recent technological contributions to the advancement of science. Discussing the impact of technology in chemistry is always a wonderful opportunity for faculty to interject examples that reflect experiences in their own careers. Second, the importance of experimental verification cannot be overemphasized. The right side of Figure 1 is dominated by theoreticians. In general, the contributions of these individuals were designed to explain phenomena that had been observed in the lab, but the universal acceptance of virtually every theoretical breakthrough was delayed until additional empirical verification was achieved. Practicing chemists are generally familiar with the expression “Theory guides, experiment decides”, but in these days of multimedia, simulations, molecular modeling, and special effects, the beginning students of chemistry may be lulled into a mind set that de-emphasizes the importance of experiments. This part of the flow chart provides an outstanding opportunity to point out that the ability to perform definitive experiments is arguably the single factor most responsible for separating the physical sciences from all other human endeavors. Third, Figure 1 provides a striking opportunity to discuss the fact that science is a process, designed to provide a better picture of nature. Spreading the same material over one or more chapters can easily cause students to miss the progressive nature of this material. Nowhere in chemistry is the idea that science is a process better illustrated than in Bohr’s work on the shell/orbit model of the atom. Bohr understood the limits of the shell/orbit model, but he presented this development because it was superior to anything that had been proposed up until that time (3, 4 ). The availability of this model provided the electron velocity in a hydrogen atom that strengthened de Broglie’s proposal that an electron could behave as a wave, and this in turn contributed to the development of Schrödinger’s quantum mechanical model. Fourth, Millikan’s work provides an outstanding case study of ethical behavior by scientists (5). The fact that Millikan disregarded a significant fraction of the data from his oil drop experiments illustrates the importance of scientific intuition. Scientists must accept the responsibility to pass on the concept of ethical scientific behavior to future generations of scientists (6, 7 ). In these litigious times it would be a blunder to think that if we behave ethically, our students will in turn behave ethically. The sciences are already falling into the trap of allowing government agencies to codify ethical scientific behavior. Unfortunately, as codified legal systems increase in complexity, individuals who are governed by them almost always move farther from basing decisions on right versus
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wrong and toward a decision-making process based on the principle that if something is not definitively prohibited then it must be acceptable. Fifth, even a quick glance at Figure 1 leads to the conclusion that over a span of little more than a half century (1870–1930) scientists from countries that had been involved in numerous confrontations, including World War I, all contributed to the development of a model of the atom that will most likely last forever.1 Although there were rivalries and personality clashes, an accomplishment of this magnitude attests to the importance of the free exchange of ideas and the power of reasoned argument. A final and more modern point that definitely deserves attention is the fact that Figure 1 is dominated by Caucasian men. Marie Curie is the single, and very notable, exception. Many of us routinely teach courses in which Caucasian males make up only a small minority of the students. Thus, unless one is sensitive about how this material is presented it is easy to alienate a large fraction of the class. In small classes, regardless of their racial or gender makeup, a discussion of this fact can often relieve tensions and may facilitate later discussions of topics like chemical and genetic similarities. In a large lecture course it may be best to simply acknowledge that, until recently, opportunities for education and research were limited almost exclusively to reasonably affluent males in industrialized countries. Though science and technology are frequently portrayed as cold and impersonal, Figure 1 clearly illustrates that scientific discovery is a complex human endeavor. The developments leading to our understanding of the modern atom, like those that helped us understand nuclear reactions and the storage of genetic information, dramatically depict scientific discoveries not as individual efforts, but as the collective work of the scientific community. Note 1. The model of the atom may evolve to better reflect experimental and/or theoretical developments. However, the model of the atom as presented in Figure 1 will always be a cornerstone of chemistry, just as Newtonian Mechanics will always be a cornerstone of Physics.
Literature Cited 1. Gillespie, R. J. J. Chem. Educ. 1997, 74, 862–864. 2. Haendler, B. L. J. Chem. Educ. 1982, 59, 372–376. 3. Moore, R. Niels Bohr: The Man, His Science and the World They Changed; Knopf: New York, 1966. 4. Murdoch, D. Niels Bohr’s Philosophy of Physics; Cambridge University Press: New York, 1987. 5. Broad, W.; Wade, N. Betrayers of the Truth; Simon and Schuster: New York, 1982. 6. Coppola, B. P. J. Chem. Educ. 1996, 73, 33–34. 7. Kovac, J. J. Chem. Educ. 1996, 73, 926–928.
Journal of Chemical Education • Vol. 76 No. 9 September 1999 • JChemEd.chem.wisc.edu
