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Zcp~t ./ & New England Association of C h e r n B c h e r s hm+ Leonard J. Soltzberg Simmons College BOS~O", Massachusetts
"Qualitative" Computing in Elementary Chemical Education
At any time in history, there are certain magic words which relate to current items of widespread attention. There is a sort of autocatalysis associated with the use of such words. Their use generates increasing amounts of related verbiage. One such word currently is "computer." The topics of computers,,computers in education, and, specifically, computers in chemical edncation have been getting much attention.' Unfortunately, the catalysis which results in an outpouring of some very' fine material can also lead to a negative effect of human behavior-inhibition by the product. For those who, for any number of reasons, have not jumped aboard the computing wagon, there may he an inhibiting effect in the proliferation of increasingly sophisticated material on Project Plato, CAI, CBE, APL, CPU's, ASP'S, and so forth. Nonetheless, while articles get more involved and plans for huge computer systems burgeon, compnters are quietly becoming ever easier to use; and increasing numbers of good, simply implemented programs are appearing in the literature. A Specific Need
The trend to easily used computers and programs is fortunate, for there appears to be a significant weakness in contemporary chemical education which the use of computers could rectify. Indeed, the time may not be distant when the computer will be an essential tool for good education in elementary chemistry. I am not thinking of the ambitious projects in computer assisted instruction in which students will absorb all wisdom from a computer-driven cathode ray screen; at least one authority has suggested that the present capability of such systems is generally overestimated (1). The computer use suggested here is modest and quite simple. I n the spectrum of chemical edncation, there is currently a particular dissatisfaction which is evident at various levels. The rumblings I refer to are typified by a passage in a recent article in THIS JOURNAL, in which the author wrote (4), "The background in chemistry of entering students who have completed Based on a lecture presented at the 356th Meeting of the New England Ammiation of Chemistry Teachers at Boston College, Chestnut Hill, Massachusetts, May, 1970. See, for example, refs. (1-9).
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the course in high school chemistry is increasingly superficial. I n large part, this appears to he a result of the "modern" courses which have been developed for use in the high schools." He went on to say, ". . . a very large number of students now enter college with some familiarity with the terminology in one or more areas of advanced chemistry, but no real understanding of them. These students have not even mastered the elementary descriptive chemistry which formerly could be expected of high school graduates." And who could miss the message of the recent cover of THIS JOURNAL (5) relating to the entering graduate student who thought - silver chloride is a green gas? What is wrong? With a measure of acknowledged oversimplification, I shall uoiut to the followincr characteristic of current chemical education. It appears that a community decision has been made to emphasize the theoretical over the observational, the microscopic over the macroscopic. It is not my purpose to debate the relative merits of the possible approaches to elementary chemical education. Certainly if a person can get to graduate school thinking AgCl is a gas, something is missing. On the other hand, the exciting theoretical advances which tie together so much observational data are an important part of the action in contemporary chemistry and also deserve attention. What I wish to show is that, to the extent to which we wish to treat the theoretical and microscopic in elementary chemistry, we can do a better job with the use of a computer. One might call the approach "qualitative" computing.
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The Role of "Feel" in Chemistry Education
Consider first the relation between the high school and college curricula in traditional chemical edncation. In high school, the student was exposed to the elements, compounds, and their reactions on a macroscopic scale. He was not expected to acquire a fundamental understanding of chemical processes, but rather to get a feel for these macroscopic entities. In college, this "feel" was reinforced and then gradually elucidated by quantitative applications and ultimately by thermodynamics. This path of development from "feel" to understanding seemed to work pretty well in the case of macroscopic chemistry. Volume 48, Number 7, July 1971
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Now suppose, as is the case, that we are going to concentrate on microscopic rather than macroscopic chemistry. As before, we cannot expect most students to develop fundamental understanding in the first course, so we ought to aim for "feel." But how does the student, lacking mathematical sophistication, acquire a "feel" for the microscopic entities of electron distributions, molecular dynamics, or mechanisms of elementary reactions? I s it by reading a book? Looking a t drawings? Listening to an inspired lecture on quantum theory? These are all part of the learning process, of course, but it is widely recognized that the student's act of doing is one of the most effective pedagogical tools; that student participation in an active rather than passive mode is an invaluable teaching asset. In the traditional elementary chemistry curricula, the student confronted macroscopic systems with which he could have real hands-on contact in the laboratory. This material, he learned well. He acquired the feel for chemical species and their behavior which was to be built subsequently into deep understanding by more detailed collegiate courses. When one addresses microscopic chemical behavior, as has been the contemporary trend, the situation changes. How can an elementary student get a real feel for kinetics systems when the fundamental formulations are differential equations? How can this student get a hands-on feel for hydrogenlie wavefunctions, say, when the mathematics involved is a challenge to most graduate students? Pursuit of these questions-how to impart a feel for these microscopic syst e m e m o s t often leads to a mathematical barrier. In this respect, perhaps, the new curricula were somewhat ahead of the times. They attempted to confront, at the elementary level, phenomena and concepts which really demanded mathematical sophistication for getting the "feel" which should be the aim of the elementary course. Qualitative Computing
"Qualitative" computing is designed to surmount this matheniatical barrier to qualitative feel so often encountered in the treatment of microscopic phenomena at the elementary level. This approach capitalizes on the evolving availability, accessibility, and usability of modern computers. In particular, the time-shared computer and the programming language BASIC, developed for such computers, can give an instructor great pedagogical power for imparting a qualitative grasp of topics in microscopic chemistry. The only in-house hardware required is a teletype with acoustic coupler and an ordinary telephone. A time-sharing vendor within reasonable telenhone distance is the other reouisite.2
Let us take an example. Certainly the invention of wave mechanics is one of the exciting developments of this century. While the early predictive promise of this theory was not fulfilled immediately, we are now witnessing a steady growth in predictive power of wave mechanical analysis for chemical systems. Surely the student of elementary chemistry should be exposed to these developments. But what aspect of wave mechanics can we meaningfully present to the elementary student when the systems are microscopic and are associated with a complex and somewhat subtle mathematics? Textbook drawings of orbitals are not the answer. However, by using a computer to handle the intervening mathematics, a student can get a qualitative hands-on feel for a microscopic system, such as the wave-mechanical atom, which will better prepare him for more detailed study later. Furthermore, this approach might even lead to a grasp of macroscopic descriptive chemistry such as periodic table correlations which today's student often does not assimilate. Consider a computer program which evaluates the radial part of any hydrogenlike wavefunction. The program asks the user to specify values for the nuclear charge, Z, the principal quantum number, n, and the azimuthal quantum number, I. The program then computes and plots on the teletype the radial part of the corresponding hydrogenlike wavefunction and the radial electron density di~tribution.~The program named WAVFN, resides in the computer's storage disk. To do the exercise, the student turns on the teletype and telephones the computer. After entering a simple sign-on message, the student types GET-WAVFN; this brings the program into the workmg area of the computer. He then types RUN.4 The program now gives the student any further instructions. It asks for values for 2, n, and I, and the student responds with his selected values-say 1, 1, and 0 for the 1s electron of hydrogen (Fig. 1). The resulting output, which is complete in about a minute, is shown in Figure 2. So what? A plot like this can be found in most
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The cast of such an arrangement varies considerably. The teletype and acoustic coupler can be rented for approximately $80/month. The cost of time-sharing service ranges from a p proximately $3/hr of non-prime connect time for a modest computer (HP2000A) to $lO/hr for prime time on a large machine (CDC3600, PDPIO). It should be noted that it is d e sirable pedagogically as well as economically to have students use the machine in groups of 2 students. A formulation is given in ref. (8). The wavefunction is often written as aproduct of functions: +(T, 0, +A) = R(r)e(E)*(+A). This program calculates only the radial part, R(r), which has no angular dependence. T h e s e commands are not standard fmm system to system hut are typical of the simple commands used on most timesharing systems.
450 / lourml of Chemical Education
Figure 1. Studentcomputer dialog needed to produse plot of the radial electron density function for a 1 r eladron of o hydrogen atom. Student entries have been underlined throughout. Figure 2. WAVFN output for Z = 1, n = 1.1 = 0. The radial port of the wovefunction is ploned in " 1 " ' s ond theelectron density function, r'R2, is ploned in "2" 'r. "X" 's indicoto intersections of the two functions. This plot rosulh from the sequence shown in Figure 1. The points of the electron density curve have been connected b y hand for clar?ty.
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Figure 3.
Student input and W A V F N ovtput for a 2r electron and Z = 1.
elementary texts, rendered in easy-to-look-at tinted halftone. There are in fact two important advantages to what has just been done. First, the student has done it himself. Second, he can generate any other hydrogenlie electron distributions he wants and compare them; he can discover trends. He might try a 2s wavefunction, corresponding to going down the periodic table. He simply types RUN again, and enters the appropriate Z, n, and 1. On examining the resulting plot (Fig. 3), the student notices that the electron density maximum is further from the nucleus than in the previous case: atoms get larger as one descends the periodic table.5 The student may also "discover" the node which has cropped up, and the fact that the wavefunction itself becomes negative in this case. Perhaps he will be far more inclined to ponder these effects if he has discovered them himself. The student might try a 2p wavefunction. Figure 4 shows the resulting plot. Suppose he now tries the 2p function with a higher nuclear charge, corresponding to crossing the periodic table from left to right. The result (Fig. 5) shows that the maximum in electron density is closer to the nucleus than with Z = 1: the atom is smaller. In addition to giving the student hands-on contact with the wave-mechanical atom, this demonstration can bridge the region between microscopic quantum theory and macroscopic properties. Such an exercise could lead into discussion of periodic correlations of acidity, ionization potential, and other properties which are related to atomic size. Here is another example. Suppose one is introducing a physical chemistry class to nuclear magnetic resonance. There might not be an nmr spectrometer available; or one might not want to devote extensive lab time to the actual use of the instrument. Consider the program NMR.' Here the student must input the chemical shifts and coupling constant and gets in return, on the teletype, a simulated spectrum for the two proton system centered a t 50 Hz. He simply types GET-NMR and RUN. The results of two such runs are shown in Figures 6 and 7. Again, The actual change in siae must also take 'into account the change in effective nuclear charge, of coune. Written by Dr. James U.Piper of Simmons College.
Figure 4.
Student input ond WAVFN output for a 2p electron and Z = 1 .
Figure 5.
Student input and WAVFN output for o 2p electron and Z = 2.
the student can systematically experiment on the computer with various values for the parameters and get a feel for the relationship of spectrum appearance to microscopic molecular parameters, a feel more intimate than he might get from a book because he has chosen the parameters. Further, this exercise is more economical of time and more accessible than a similar study would be on the actual instrument. I must emphasize three points about the "qualitative" computing approach. First, I do not mean to imply that the computer replaces an instrument or laboratory experimentation, and we must be careful not to give the student the impression that it does. This use of the computer serves the purpose of giving a physical feel for microscopic systems when there is a mathematical barrier which would otherwise obstruct the beginning student. It helps the student develop an intuition for microscopic systems in the hands-on way he could develop intuition for laboratory scale systems. The second point is that we as teachers do not have to be systems engineers to use this approach. As computers have become more sophisticated, they have quietly become easier to use. The very simple system commands used in the foregoing examples are typical of those required for most current time-sharing systems. Finally, one does not have to be a master programmer to use the computer to advantage. The pages of this Volume 48, Number 7, July 1971
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and other journals frequently contain descriptions of useful, adaptable teaching programs. These can be used by persons with limited programming experience. Indeed, it is likely that teaching programs of this sort will come to be devised and circulated on the same basis as overhead projector demonstrations. Once exposed to the excitement of such computer applications, the reader will want to try his own hand. The programs WAVFN and NMR, available from the author, are written in the language BASIC. This programming language is especially easy to learn, very powerful, and almost universally available on time-sharing computers.
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