Robert I. Walter
Haverford College Haverford, Pennsylvania
Two-Track Introductory Chemistry
The development of new secondary school programs in chemistry and the other sciences, and the expansion of the advanced placement program have led to substantial improvement in the knowledge and scientific sophistication of many students in the first year college chemistry course. Even students who have not studied one of the new programs have benefited from the general upgrading of secondary school science education which has resulted. These changes have produced serious problems in placement and course structure for the undergraduate college program in chemistry. Provision must now be made for identifying and continuing the training of entering students whose backgrounds range from no chemistry (and sometimes little other science) to the equivalent of two years of college work. The introductory courses now in operation at Haverford College provide a good deal of flexibility in meeting these problems, and may be of interest to other institutions on that account. Haverford is a small liberal arts college for men which is now embarked on a planned expansion to 700 students. The selection process brings us students who generally are able; not all of them are willing, however. Haverford tradition favors a common liberal background for all students, attained in part by a
Presented at the Third Delaware Valley Regional Meeting of the American Chemical Society, Philadelphia, Pa., February 25, 1960; Abstracts p. 15.
rather heavy program of required courses distributed among the divisions of humanities, social sciences, and natural sciences and mathematics. This tradition is opposed to early specialization or over-professionalization of the currirulum. Thus, we need a course plan which will handle students with a wide range of backgrounds in science, and will contribute a t the introductory level to a common liberal background for all students. Larger institutions usually respond to these multiple demands by offering several introductory courses which differ in both pace and content; students are assigned to them according to secondary school background and probable major. Two courses of this sort were offered a t Haverford until seven years ago. The best prepared and most interested (because of professional goals) students were assigned to a conventional course in general chemistry. Poorly prepared students, and those looking for the easiest way to meet the science elective requirement, went into the second course. As a result, students in the latter never observed other members of their classes who were enthusiastic or able, and this experience tended to confirm their preconception of science as uncreative, dull, and unworthy of intellectual effort. The result was an apathetic classroom atmosphere which was difficult for any teacher to overcome, however great his abilities and enthusiasm. This defect of the old system has been eliminated by assignment of students to the introductory courses on a new basis, described below.
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Different Pace for the
Same Content
Our current response to these multiple demands is to offer two introductory courses with the same content but differing in pace, in order to provide for students with widely varied backgrounds or interests. One covers the material in two semesters, while the second does so in only one. (Some topics are handled as assigned reading, without lectures, in the onesemester course.) These courses must offer something new and stimulating to students who are relatively well prepared. At the same time, they must not be too difficult for students with weak backgrounds or principal interests in other areas. Success in meeting these requirement,^ depends heavily upon the selection of topics covered in these courses. The principal emphasis is on the organizational bases of chemistry-the periodic t,able and the notion of functional group. Structural concepts-atomic, molecular, and crystaland the nature of ionic and covalent bonds and the resulting properties of subst,ances so formed are treated in detail. Some attent,ion is given to the conservation laws and stoichiometry, chemical equilibria and the problems of kinetics and mechanism. The best prepared students (but not all of those who eventually major in the department) take the one semest,er introductory course. They follow this with a semester devoted to the first and second laws of thermodynamics, and a detailed treatment of chemical equilibrium. This provides early contact with the rigorous side of the subject, and is the first course in a threesemest,er sequence in physical chemistry. The cont,ents of the introductory courses are discussed in greater detail below. Students are assigned to the introductory courses on the basis of a placement examination of our own design, with high school and advanced placement grades considered as support,ing data. Roughly half of the examination questions are elementary problems on stoichiometry and the gas laws. The others are more directly related to the major material of the course; struct,ures of atoms and molecules, shapes of atomic orbitals, and so on. No student is excluded from chemistry courses by his performance on this exam. Students who achieve grades below 60 have been a s signed t.o the twosemester course, and those with grades above 70 to the one-semester course. We have had very few students with placement grades between these figures, due to the nature and distribution of the questions used. Students with very high grades are offered the option of going directly into the sophomore organic course. If they do so, they add the first course in physical chemistry during the second semester, so that the work of their first year takes them through two years of our normal program for majors. Students who are hesitant about moving ahead this rapidly are not urged t,o do so, since a substantial degree of selfconfidence is necessary to carry a freshman through a program a t this pace. No placement procedure is infallible. We provide a margin for error by scheduling lectures simultaneously for the two introductory courses. An examination is given early in the one-semester course, and students who do not demonstrate their ability to master the m a terial at the pace a t which it is given are asked to 202
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transfer to the slower section; they can do so without scheduling problems. We have been pleased with the results of this program during two years it has been in use. The small group of students assigned directly to the organic course has done very well there. A few students have been asked to move to the two-semester introductory course after initial assignment to the accelerated course. They did not sufferacademically as a consequence. Enough able but less well-trained students have remained in the two-semester course to serve as a model to other members of the class. No one has complained about assignment to the slower section; the choice and level of material covered is such that students from good high school programs are not bored by a year-long rehash of the high school material. The selection of topics for the introductory courses a t Haverford has been determined by our desire to provide course material rather different from that found in the usual high school courses, to provide a better perspective on the entire field of chemistry and what chemists are concerned with today than do the conventional courses in general chemistry, and to provide for early treatment of organic chemistry and biochemistry (both given as sophomore courses, the latter in thc biology department) from a reasonably sophisticated level which includes the discussion of kinetic evidence for reaction mechanisn~s. Topics which have been covered are listed in order below, together with the approximate number of weeks devoted to each in the year course.
Outline of Introduction to Chemistry Week.;
Tonic chemical formulas and stoiehiometrv atomic structure, atomic spectra, and the periodic table energy and enthslpy changes in chemical reactions properties of gases (without kinetic theory derivation) properties of solutions and chemical equilibrium descriptive chemistry of selected groups classification of tvnes of chemical bonds purification met6dds and criteria of purity structures of crystals struotures of covalent molecules the functional group concept ability of elements to form covalent bonds historical development of the quantum theory atomic and molecular orbitals and the properties of covalent bonds and of covalent molecules metal complex ions reaction kinetics and mechanisms
Some comments on this list will indicate more clearly the level of the treatment. The notion of a periodic arrangement of elements is developed both empirically and as a consequence of atomic structures postulated from atomic spectra and related experimental data. Descriptive chemistry is confined to selected groups. The classic experiments which led to development of the quantum theory are given as background for postulating a wave equation. The methods for its solution are not considered, but the consequences for the case of an electron in a one-dimensional infinite well and for
the hydrogen atom are discussed in detail. This background is used for the discussion of directed orbitals, sigma and pi bonds, and bond lengths, bond angles, isomerism, and polarities in covalent compounds. Examples are taken not only from carbon compounds, but from those of other elements as well. Every effort is made to make clear the experimental basis for each topic. I t will be not,ed that the program is restricted to a relatively small number of topics. Each of these is carried as far as possible a t the level of training of first-year students. In general, we go beyond the level at which these topics have been considered in traditional introductory chemistry courses. Most of the topics have been developed sufficiently to be applied in subsequent courses without additional discussion; they are not considered again in later courses until sufficient additional background has been provided to permit work at a substantially more sophisticated level. Repetition of the quantitative treatment of chemical equilibrium is deliberate; it seems to be necessary in order to make the training effective. This material has been offered in the two-semester course for the past eight years. We are generally pleased with the results. It is true that if we were to plan an introductory course for chemistry majors only, the selection and treatment of topics would differ somewhat from our present scheme. The concessions which we make in order to offer a course suitable to all students we justify by our belief in the benefits of liberal education. One significant gain in efficiency results in offering introductory courses which differ in pace, but not in content: subsequent courses in the chemistry sequence need not take account of students with different backgrounds. Organic and biochemistry can be offered from the beginning a t a more sophisticated level than is possible when all of the material on bond types and stereochemistry must be developed in those courses. Restriction of the introductory course to a relatively small number of topics which are treated in considerable detail has the advantage that the courses in physical chemistry are not spoiled for many students by a prior superficial treatment of many topics. Exposure to quantum mechanics at a descriptive level arouses the curiosity and interest of the students; they want to take the full course in quantum mechanics as seniors. We have been conscious that this course underemphasizes topics which are treated on a rigorous quantitative basis, but we feel that this deficiency is overcome by the early introduction of thermodynamics in the first semester of physical chemistry, which the best students take as freshmen. Laboratory Work
The selection of laboratory work to accompany this course has been somethmg of a problem. Experiments for the first semester taken from standard laboratory manuals have not been satisfactory. We are now moving in the direction of greater emphasis on spectroscopy and quantitative determinations. A number of new experiments have been developed for the second semester, and a few others are based on published material. A list of titles for the experiments which have been used during the second semester follows:
Models of Crystal Structures (a modification of Drtvidson's' procedure) Separation by Recrystallization (potassium and copper(I1) nitrates separated in aqueous nitri&cid) Se~arationbv Distillation (acetone and acetic acid: methanol and cycloh&anol) Oxidation of Secondary Alcohols: Acetone from Isopropyl ~
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Composition of the Silver-Ammonia Complex Ion (a modification of Wolfenden's procedureP) Geometric Isomerism: IXmethyl Maleate and Dimethyl Fumarate Complex Ion Formation and Ion Exchange (separation of iron, cobalt, and nickel) Rates of Chemical Reactions: Reaction Rate and Equilibrium State Rates of Chemical Resotions: Concentration and Temperature Effects The Solubility Product of Lead Iodidea Isolation of a Natural Product: Lactose from Milk.'
Nearly all of these experiments are in use for the eighth year. A number of them presuppose considerable familiarity with quantitative procedures (sampling, and use of a buret and pipet, for example). Some of them have become less useful recently because similar work has been prepared for the CHEMStudy course: an experiment on crystal structure models, on geometric isomerism, and one on the ion exchange separation of Fe(III), Co(II), and Ni(II).S We have not been unaware of the stimulus to able students of laboratory work of the "research problem" type. However, it is highly desirable to insure a hackground of common laboratory experience for students who go on to advanced courses. We have also found that even able students tend to bog down if given too much freedom to plan their own work on experiments of some complexity. They need the satisfaction derived from snccessful results. We have chosen to meet these somewhat contradictory objectives by assigning experiments which all students (except those who clearly have already done substantially the same work) are expected to complete. At the same time, we try to provide an "open end" problem in addition to the assigned laboratory work by appending appropriate questions to each experimental procedure. Some free time is made available for students to try these problems or to repeat experin~entswhich they feel have been unsuccessful. This compromise appears to meet adequately the requirements of students who differ substantially in laboratory experience and ability.
DAVIDSON, N., J . CKEM.EDUC.,29,249 (1952). WOLFENDEN, J. H., J. CHEM.EDUC.,36, 490 (1959). 3 This experiment has been modified from that in VOSBURGA, W. C., AND WILDER,P., "Laboratory Manual of Fundamentals of Analytical Chemistry," published privately a t Duke University, Durham, N. C., 1956, p. 20. The experiment is basicdlv similar to that of GOODMAN. R. C.. AND PETRUCCI.R. H.. J. CLEM.EDUC.,42, 104 (1965). ' 4 This isolation procedure works quite well, hut it has the disadvantages that it involves a slow filtration step and gives a. product which is not readily checked for identity or purity. I t cannot be distilled, and it has no melting point. Far these reasons, we have not used the procedure recently, and we have no satisfactory experiment which illustrates the isolation of a natural product. $MALM,L. E., editor, "Laboratory Manual for Chemistry, an Experimental Science," W. H. Freeman and Company, San Francisco, 1960, pp. 69, 72, and 92. 2
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