The Physical Chemistry Sequence at Liberal Arts Colleges The Lake Forest College Approach George C. Shields Lake Forest College, Lake Forest, IL 60045 The physical chemistry sequence a t liberal arts colleges throughout the country typically spans two semesters. This junior year course has traditionally consisted of a semester focused on thermodynamics, followed by a semester of quantum mechanics. At most colleges kinetics is taught in the second semester, but in some it is placed in the first semester along with thermodynamics. If statistical mechanics is covered, it is in the second semester. Of the 14 liberal arts colleges in the Aswciatt!d Colleges of the Midwest.' five rewire unl\. on(, semester of physical chemistry for the che&istry major. The course content of the required first semester is devoted primarily to thermodynamics. Serious chemistry majors with graduate school aspirations typically elect the second-semester course, required for a n ACS-accredited degree. Many colleges have an advanced course in physical chemistry available as a senior elective. In a recent Prouocatiue Opinion, Moore and Schwenz argue that the problem with the physical chemistry course is that the traditional approach does not convey the excitement of modern physical chemistry research ( 1 ) . They state that the low annual rate of growth in the number of physical and theoretical chemistry PhDb from 1978-1990 and the dramatic decline in the number of bachelor's degree chemists in the time period 1970-1990 indicate the lack of interest students have in the physical chemistry course. Their solution is to revamp the physical chemistry curriculum. Specifically: (1)reorder the cumculum placing quantum chemistry and spectroscopy in the first semester; (2) start the second semester with chemical dynamics, followed by thermodynamics; (3) teach statistical mechanics last; (4) modernize the laboratories by using more modern equipment, particularly lasers; and (5) reduce the lab write-up requirements. Lake Forest College Course In this paper I describe our efforts a t Lake Forest College to revamp the physical chemistry course implemented in the fall of 1989. That year marked a change from the traditional format. I n the previous course thermodynamics was covered in the first semester, kinetics in the second semester, with a few weeks of quantum mechanics added a t the end of the second semester. A third course in quantum mechanics was offered a s a senior elective. I n the new course sequence, quantum mechanics and spectroscopy are covered in the first semester, followed by a second semester with equal attention given to thermodynamics and kinetics. My reasoning for this change was primarily hecause spectroscopic techniques are fundamental to the study of chemistry, the way we "see"mo1ecules. While students are introduced to spectroscopy in some freshman and all organic courses, the principles that these tech-
niques depend upon cannot be developed in detail. One must understand quantum mechanics to understand spectroscopy. Learning quantum mechanics takes on new meaning to students when they realize that a direct benefit of learning the material will be understanding the physical phenomena that infrared, W m s , and NMR spectroscopies are based upon. The theories of the harmonic oscillator, the rigid-rotor, and electronic potential energy curves become interesting when applied to experiments involving infrared, infraredlmicrowave, and UVNis spectroscopies. Quantum mechanics is too important to be left to the last few weeks of the year, or to be optional. In addition, kinetics is as important a s thermodynamics; equal amounts of time should be devoted to each subject in the second semester. Modern quantum-mechanical calculations have become a useful guide to experimental science, and the interplay between theory and experiment is a t the forefront of research in physical chemistry. The focus of this curriculum is molecular. We should motivate our students' interests in learning physical chemistry and prepare them for modern physical chemistry research by ensuring that they are well-versed in a molecular approach. Adding to the cumculum necessitates deletions of other material. In our approach we cut half of the material in the traditional semester-long thermodynamics course. Table 1presents the topics covered in each semester of physical chemistry a t Lake Forest College (2). Cuts in thermodynamics include: phase equilibrium for one-component systems, ideal solutions, and non-ideal solutions; electrochemistry; and surface thermodynamics (3). Of these topics, electrochemistry is covered in a required analytical chemistry course and a n optional instrumental analysis course (required for the ACS major). The other topics can be learned in a third optional undergraduTable 1. Suggested List of Topics in the Physical Chemistry Course (2) Fail Semester
Spr~ngSemester
Quantum Theory Atomic Structure Molecular Electronic Structure Molecular Quantum Mechanics Rotational and Vibrational Spectroscopy Electronic Spectroscopy of Molecules Magnetic Resonance Spectroscopy
Properties of Gases First Law of Thermodynamics Second, Third Laws Gibbs Energy Chemical Equilibrium Statistical Mechanics Kinetic Theory of Gases Experimental Gas Kinetics Theoretical Gas Kinetics Kmetics in the Liquid Phase Photochemistry
'The Associated Colleges of the Midwest (ACM) are Beloit College, Carleton College, Coe College, The Colorado College, Cornell College, Grinnell College. Knox College. Lake Forest College, Lawrence University, Macalester College, Monmouth College, Ripon College, St. Olaf College, and the College of the University of ChiVolume 71
Number 11 November 1994
951
Table 2. The Physical Chemistry Laboratory at Lake Forest College Fall Semester Weeks #I3
Weeks
Spring Semester
Atomic Line Spectra (6) Project labs throughout Franck-Hertz Experiment (7) the semester; wrinen Blackbody Radiation reports turned in after each project. Graphics Model Buildinga
#4, 5
Weeks #68 Weeks #9-14
MOPAC (8-10) Spectroscopy (12-16)
Final week devoted to oral reports.
.
"Cnem 3D P A sara aoefrom Camor age Sc en111c C o m o ~ng l lnc CSC Camor age. MA We .se Cnem 3 0 P .s for mwe OL !o ng anc MM2 m n m zaI on on a Macnlosn, ana lnen w o n tne cooro nates !o lne $AX lor MOPAC CP C. a l m s Tnen we rnport ina ovim ZM coolo nales O ~ C LIO Ine Mac nmsn an0 examlnelne nerv cooro nalos w :n Cnem 30 P .$ W e a so .se C n e ~ l D ' w lram CSC la produe I na f g ~ e %m s lne o ~ : p coord ~ l na'es.
ate course, a t the graduate level, or as research interests require. Why address quantum mechanics and spectroscopy prior to thermodynamics? Traditional physical chemistry textbooks are written from the vantage-point of learning thermodvnamics before auantum mechanics (4). Is there any r e a i advantage to tkis approach? My students find thermodynamics a s difficult (and the mathematics just as formidable) a s quantum mechanics. Thermodynamics looks easier, but the subtleties of thermodynamics are difficult to learn. I n addition, a firm understanding of the molecular world makes the interpretation of thermodynamic processes more meaningful for students. An additional advantaee of taking quantum mechanics in the fall of the junioruyear, a t our college, is that a student can take the inorganic course offered in the spring semester, concurrent with the second semester of physical chemistry. The best reason may he that espoused by Moore and Schwenz in this Journal (I): teach quantum mechanics and spectroscopy first to convey the excitement of modern physical chemistry. First-Semester Physical Chemistry Laboratory Modernization of the phvsical chemistrv laboratory program is the goal of a co&rtium of mid-Atlantic colieges, a s well as many individual instructors (5).Table 2 presents the laboratory associated with the Lake Forest College nhvsical chemistm cumculum. I n the fall students first wdrk on laboratory experiments that illustrate the fundamental concept ol'quantizutim, such a s atomic line spectra 16'1 and the Franrk-llortz experiment (71.The idea is that if students b d i e ~ rthat mirrosropic matter is quantized. they are more likely to appreciate the development of quantum mechanics, and they are motivated to learn. These experiments a r e followed by calculations a s auantum theory is develooed further. Currently, we perform semiempirical quantum-merhaniral r a l c u l a r i ~ ~ n s with MOI'AC 18-10,, because this promam uIlo\vs students to calculate reactants, products, &ansition states, and reaction pathways for organic reactions using available computers. These calculations allow for continuity in the chemistry curriculum, a s students review some organic chemistry when selecting a reaction to model. Computational chemistry has become a n important discipline; a thorough grounding in computer graphics model building and quantum-mechanical techniques fits well into the modern physical chemistry course.
952
Journal of Chemical Education
Accuracy of a b initio calculations has improved dramatically, and computational results now guide experimentation under favorable conditions; students should learn that quantum mechanics is a pertinent field with practical importance beyond calculation of the hydrogen molecular ion (11).The low cost of semiempirical computations enables students to work on larger organic systems, and mistakes can he made without tremendous losses of time. The time element is important since students learn by doing, and huild up their experience gradually. Our calculations are done on a VAX 4300. We have used a microVAX 3400 a s well. Faster computers would enable students to renroduce a b initio calculations that have led to reinterpretation of experimental data, showing the predictive Dower of modern comoutational chemistrv (111. The computational segment of the laboratory is followed by spectroscopy experiments (12-161. Experiments in the infrared region are emphasized, because that is where we have state-of-the-art instrumentation. Laser experiments (1,5,17) should play an essential part in a modern lab and this aspect of our laboratory is being developed. The introduction of low-cost lasers allows for exneriments in the visible reeion a t hieher resolution than th;! traditional departme& U V - ~ i ispectrophotometer can obtain. Lasers also allow for the develooment of other types of spectroscopies such as Raman. Second-Semester Physical Chemistry Laboratory Our s ~ r i n esemester laboratorv " is z~roiect-based.Each of the st;de& in the lab develops a n iidividual project. Each is res~onsiblefor doine librarv research. desienine and developing the experimental approach, analyzing the results, writing a comprehensive final report, and communicating his or her results to the rest of the class through a n oral report. The better the student, the more ambitious the project. Weaker students tend to pick a n experiment out of one of the standard laboratory manuals (121, and complete more projects during the semester. Examoles of nroiects students have chosen include: " building a nitrogen laser (18); assembling and testing an Enraf-Nonius X-rav precession camera: usine the orecession camera to determine the space group, cell dimensions, and molecular weight of proteins (191; studying enzyme kinetics of alkaline phosphatase; determining the rate of reaction between acetone and bromine (20): eas thermomet r y (21); heat capacity ratios for g-ase; 'i22), helix-coil transition in polypeptides (23); designing and supervising the construction of a temperature cell for FTIR spectroscopy; using a dye laser to examine the fluorescence spectrum of iodine; performing bomb calorimetry on glucose (24); building a buckyball reactor (25-26); combining the keto-enol NMR tautomerization experiment (27) with molecular quantum-mechanical calculations; and combining mass spectrometry (28) with quautum-mechanical calculations. I tell students the aim of this laboratory is to start transformine them from students to scientists., bv " eivine them a taste of the research process. Laboratory time is four hours per week. Many students are so excited about their own project that they work additional hours throughout the semester. Students write UD their reports as thev complete each project. At the end of'the semeiter each st;dent prepares a 10-minute oral report covering one project, and presents it to the class.
-
- -
.
".
-
-
-
Conclusions The model sueeested bv Moore and Schwenz (1)has .... heen largoly implc~menteda t Lake Forest College since 1989. llas this ncw curriculum made a difference"Thls IS a difficult question to answer. At small liberal arts colleges like Lake Forest College the physical chemistry course
usually is not a major factor in the dropout rate of chemistry majors. Students who are successful in organic chemistry have developed the work habits required to succeed in chemistry. The attrition rate of chemistry majors a t the junior-year level was low with the old curriculum and remains low in the new curriculum. What does appear to be true is that physical chemistry as a subject has a better reputation among the students. Sophomores who talk with other students and the faculty do not talk of avoiding PChem. The chemistry faculty here do not perceive the physical chemistry course as a barrier to attracting chemistry majors. Sophomores know PChem is hard, but they believe it is a relevant and interesting course from what the upperclass students tell them. Over the past two years the number of chemistw" maiors has been increasing. " -. even a s the College a s a whole is experiencing a decrease in enrollment. Moore and Schwenz attribute the dramatic decline in the number of bachelor's degree chemists to the lack of interest students have in the physical chemistry course ( I ) . Our experience suggests that the new physical chemistry course sequence a t Lake Forest College is interesting to the students and a t the minimum is not responsible for losing our students'interests in chemistry? The other statistic that Moore and Schwenzcite is the low annual r a t e of erowth of ~ h v s i c a land theoretical chemistry PhD's from 1978-1960,'again indicative of a n unexciting physical chemistry course. At Lake Forest College, 26 graduates went to graduate school in chemistry during the 1978-1989 time period. Of these 26 students, only one went into a physic& theoretical, or biophysical chemistry graduate program. Of the 3 1 students who started the physical chemistry sequence from 1989-1992, 30 have majored in chemistry. Fifteen went on to undergraduate research projects (eight in physical, biophysical, or computational chemistry). Of the 20 students who took the new physical chemistry sequence and graduated to date, four have gone to graduate school in chemistry, eight have gone to professional school, and eight are working in industry. Of the four students in graduate school, two are in physical or biophysical research programs. These small numbers of students do not allow a rigorous evaluation of the new curriculum, but the trend is certainly encouraging. I feel that the program is a success, because students are not turned off by the material. They understand the foundations of spectroscopy. They appreciate the role of computational chemistry, and they are better prepared for modern physical chemistry research. What about our premedical students and students going into industry? Does this model apply to them? I think it does. If we want to develop chemists trained to use and 2The Fall 1994 enrollment in physical chemistry is 20 students. Lake Forest College has a total enrollment of just over 900 students.
understand spectroscopic techniques in industry, then we should build that foundation in uhvsical chemistry If we want our future medical doctorsto~appreciatenew developments in computer-assisted drug design, then we should make sure that our premedical students take quantum mechanics, build molecules with computer graphics, and perform calculations. The discipline of physical chemistry, founded by van't Hoff, Arrhenius, and Ostwald in the 1870's and 1880's (291, was based upon thermodynamics. The development of quantum mechanics in the 1920's transformed ~hvsicalchemistrv into a molecular science. To ensure that all our students learn the molecular foundations of modern chemistrv. auantum mechanics and spectroscopy should be covere"d &st in the physical chemistry course sequence a t liberal arts colleges.
..
Acknowledgment I am grateful for my physical chemistry students, who continuallv educate me. and for mv collearmes in chemisl in try. I espe>ially thank Lee ~ h o m p s o na n d ~ i l Martin chemistw. and Michael Kash in -uhvsics. - . for their encouragementand support. Literature Cited 1. Moore, R. J.;Schwenz, R. W. J Chrm.Educ IS=, 69,1001-1002. 2. Alberty, R. A P h y s i d Chemistry, 7th ed: Wky: New Yo*, 1987: Chapters 1-5, 11-23.
9. 10. 11. 12.
13. 14. 15. 16. 17. 18. 19. 20. 21 --
22. 23. 24. 25. 26. 27. 28. 29.
ington. IN. Gil1iom.R. D. J Chem. Edue 1989.66.47-50. Lilhe, T. S.:Yesger, K J Cham. Edur l889,66,675676. Sehaefer. H. E SeGnco 1986.231,110&1101. (a) Sime. 8. J. Physvol Chsmislry: Methods. Tochnqups and Erpwimmts; Samden: Chicago. 1990;pp 660-668. (bl Malthews, G. P. Erperimntol Physiml Chemistry; Clarendon: Oxford, 1985; pp 253.261 (cl Shoemaker, D. P.; Garland, C. W ; N,hler J.W E z p ~ r h e n t sin Physiml Chemistry, 5th ed; McGraw-Hill: New York, 1589; pp 497-507. Ref 120: pp 676687. Ref 12c; pp 461468. Moog, R. S. J Chrm. Educ 1991,68.506508. Ref 12c; pp 4466451. Henderson, G. J Chem. Edue. 1987.64.88-90. GTIeneieen,H.-PTheNiLwen h e r - P u m p e d 4 y e L " c A n I d d L i g h t Soume for College Ezperimnts; Laser &ienee. Ine.: CarnbTIdge. MA. 1984. Bergmann, E.E.Reu. Sei. Inatrum. 1971.48.545-546. Knox, J. R. J. Chem.Educ. 1972,49,476479. Ref 120; pp 621-628. Rpf ib nn R M h ~ Ref 12c; pp 10P118. Ref. 12c: pp 38M89. ~~
~~
Charnpi0n.T. D.;Schwena,R.W. J. Chem. Educ IW,67,528-529. lacoe. D. W.: Potter W.T.: Teeters. D. J. Cham. Educ. 199265.663. Craig. N. C.: Gee, G. C.: S o h n s o n , ~R. . J Chsm Educ 1k2.89.664-666 Ref. I Z C : m2-m Ref. 226; 170-183. Bemoa, J. WPhysiml C h i s f r yfrom Ostluold to Pouling: The Makingofa Scrsnn m A m r i m ; Pdneefon: Princeton, N J , 1090: pp 1-45.
.
.
ip
Volume 71
Number 11 November 1994
953
