In the lectures, more-or-less developed in a classic fashion, the professor presents each topic and describes the main points. During seminars students must solve problems or answer ouestions related to the lecture. This task can be done as homework or during the seminar time. Students mostly prefer to do it as homework and to employ the seminar time to discuss the answers with other students and with the ~rofessor.Students s~ontaneouslvform discussion groups; and the professor does not explicitly give the answers, but he guides them to fmd the answers. Seminars are taken as informal classes where students have more freedom than in a classiclecture, givingto the professor the opportunity to discover their difficulties and to help them in a more personalized way. Laboratory classes consist of selected experiments that enable the students to reinforce the concepts, to acquire the necessary experience in performing basic physicochemical calculations, and to get hands-on experience in a laboratory. Course evaluation is performed at two levels. At the first level teaching assistants evaluate the ability to perform calculations and the performance of students a t the laboratorv. The second evaluation is done bv the ~ r o f e s s o r through five cumulative examinations. Basic exams are prepared for all the students. When a student shows difficulties with one or more topics, special questions are added to a subsequent test in order to determine if the difficulties previously encountered have been solved. Once the tests are evaluated, they are discussed with each student during personal interviews in order to mark the topics needed to be reviewed. The Inorganic Chemistry Course The goal of this course is to introduce the student to the studv of chemical and ohvsical nrowrties. as well as the behakor, of the elementk i n this'coirse wemix descriptive inorganic chemistry with structural chemistry in order to minimize the memorization needed in a traditional descriptive course. We begin by developing the basic concepts related to atomic, molecular, and hybrid orbitals. Then l each mu^ of elements is vresented with s ~ e c i aattention to the main properties of the elements bklonging to the group, natural occurrence, isolation, purification, laboratory and industrial preparation methods, the most important compounds and their historic and modem uses, always of the most relevant elements. Environmental aspects are introduced in different parts of the course as an example of the role of chemistry in solving problems; new materials are mentioned in order to show the role of chemistry in the improvement of our life quality; some examples are given where chemistry contributes to the solution of interdisciplinary problems. We take each opportunity to show how chemistry is present in our lives and its social and cultural consequences. The lectures given by the professor are complemented with seminars having the same organization and purposes of those corresponding to the general chemi ~~-t"n course. r -The laboratory is devoted to the preparation and characterization of several elements and their compounds. These activities are comolemented with the oreoaration., bv the students, of mondgraphs that require a relatively simple biblioera~hic - . search. This is done to develoo w r i t i n ~skills and because writing is also a very important activity that contributes to the learnine Drocess. The evaluation of students is decided in the same' way as in the general cbemistry course. Under this new organization, the inadequate physical and mathematical backgrounds usually encountered in our students were partially dealt with by placing the general chemistry course in the second semester of the first &
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Journal of Chemical Education
career year followed by the inorganic course. The teachine staff is-the same for 6 t h cours& assuring a great degree of content homogeneity and methodological continuity. Another advantage of having the same teaching staff is that we know exactly what we have taught in general chemistry and what le&l the students rearhed: tKcrefore, we can introduce minor corrections each year. Thin aluo avoids the danger of performing drastic changes that usually result in failed experiments with the consequent damage in the formation of our students. We also devote a few minutes - ~ - -~ - ~- at -~~ the beginning of each class to explain the importance of the t o ~ i c discussed s and how thev will relate to tonics that will b'introduced later in the co;rse. For the students the new methodology implies much more personal work than in the past, nevertheless, they do not disamee with it because under this svstem thev nlav a n activerole in the learning process. students are a&k&l to attend the seminars with their books and any other source of information that they consider useful. When they spontaneously form working e r o u ~ sthev feel free to express their opinions within thegroup beciuse they are not afraid of making mistakes and to be corrected by other students. When the group fails to find the answer to a question or problem they ask the professor or assistants for help. While evaluating this new system our first conclusion is that perhaps it is not so impor& to discuss which fundamentals must be taught but, rather, the way in which we teach them. Our experience, which was basically a change in methodology with a minor revision in the contents, sup~ o r t this s conclusion. This new svstem reouires the r~ nrofes~ Lor to be very efficient with respkct to th;time he devotes to each subject and simultaueously to judge how deeply to delve into each topic. We have obtained better results teaching models and subjects that students could use in the near future. We found that it is better to reduce the time devoted to lectures in favor of seminars for the reasons previously mentioned. ~
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Models and Molecules: A Laboratory-Based Course in Spectroscopy for the Nonscience Major T. C. Werner and L. A. Hull Union College Schenectady,NY 12308
Recently, the faculty a t Union designed a new General Education curriculum, requiring all students to take two courses in basic or applied science, one of which shall haw laboratories. This requirement has led to the development of several new laboratory-based courses in science for nonscience majors. Models and Molecules, a chemistry course for nonscience majors and the the subject of this paper, is an example of one of the new courses developed for this curriculum. Course Objective and Rationale The course objective is to introduce chemical ~ r i n c i ~ l e s to nonscience majors through the use of meas&ements with modem scientific equipment. We believe it is important to introduce these students not only to the way that chemists think but also to the types of tools that the chemist uses in the late 20th c e n t u 6 . h the process, we hope to demonstrate why these tools are required in modern chemistry. Finally, modem chemical instrumentation is increasingly expensive to obtain and maintain and can be more Presented at the Natonal Amencan Chemlca Soc~etyMeetmg n San Franc sco (Apr 1992) as pan of the 'Sympos Lm on Teach ng Sclence wlth a Tecnno ogy Focus The New Ltoera Ans Program
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readily justified at a school like Union if more t h a n just science majors receive t h e benefits from such equipment.
At this point we introduce the concept of multiple bands by having students apply the data in the above table to alkenes, alkynes, carbonyls, and nitriles. In concert with these model-building exercises, w e introduce the following concepts: the difference hetween molecular and structural formulas; the geometry about atoms with single, douhle, or triple bonds; isomerism (including eistrans): KekulC formulas. line formulas. and how to show three-dinwnuhnal structure in lwo dimens& We also mrlude rules of nomenclature for all of the molecules that the students build and stress the recognition of functional groups.
Course Format T h e course meets once a week for four hours during t h e 10-week academic term at Union. E a c h meeting h a s i o m bined lecture a n d laboratory work, with emphasis on t h e latter. Course size is restricted to 15 students. No text is required for t h e course, b u t readings a r e assigned from World of Chemistry by Joesten, Johnson, Netterville, a n d 111. Use of Mass Spectrometry (one class) Wood (Saunders, 19911, w p i e s of which a r e placed on liWe have students build models of acetone and methyl ethyl keh r a r v reserve for student use. Several Droerams o n video tapeWfromt h e World of Chemistry series ( & ~ n e n b e r ~ / ~ tone ~ ~ (MEK) and then ask them in what way are they different. Students quickly see that MEK is larger, which leads directly to Collection) a r e assiened for students t o view a s homework. the concept of molecular weight. We emphasize that the two molThe course grade icdetermined by a midterm exam (25%), ecules can be distinguished on the basis of molecular weight and a final exam (25%) a n d on written a n d oral homework asthat mass spectrometry is an instrumental method to determine signments (50%). molecular weights. In our conceptual approach to mass spectrometry, we begin by telling students that molecules must be tagged in some way in order for the mass spectrometer to be able to disCourse Focus and Approach tinguish among them an the basis of molecular weight; that this T h e instrumental focus of t h e course is on svectroscovic tagging i s done by converting the molecules into positively methods. However, w e introduce students to i h e basics of charged ions and that the resulting ions have a path in a magnetic molecular structure through the u s e of simple ball-andfield that is dependent on their mass-to-charge ratio (mle). We stick models. Spectroscopic methods a r e t h e n employed to point out that the molecular weight can be determined from the mle ratio of the parent ion peak, since the charge is usually one. verify predictions from t h e s e simple models. Ideas a n d Students then obtain mass spectra of acetone and MEK and find concip& a r e introduced on a need-&-know basis a n d more parent ion peaks at the corredt molecular weights for the two malb y experiential learning t h a n b y direct lecture. For examecules. We then ask them what the other peaks in the mass spec~ l ,e once . students know the rudiments of oreanic structrum might he due to. They can readilv conclude that all of the ture, they a r e shown I R spectra of a variety of organic molother major peaks are small& than the parent ion peaks and thus ecules. They first develop t h e idea of pattern recognition; must represent pieces of the molecules. This gives an opening to that is to say, they begin to notice t h a t similar molecules discuss simple fragmentation patterns using the two spectra for h a v e m a n" v I R Deaks examples. . i n common. Later. thev eventually a r e lead to figure out that IR spectra co&iiinformati~n on IV. Identifying Molecules with IR Spectroscopy specific groups of atoms i n t h e molecule (IR spectra a s (two to three classes) functional group indicators). In this section, we start with a brief discussion of the nature of Course Outline electromagnetic radiation, including the location of the IR region and the relationships among energy, wavelength, frequency, and wavenumber. We define spectroscopy a s that area of science dealI. What is Chemistry? (one class) ing with the interaction of electromagnetic radiation and matter. a. States of matter a n d physical changes. We do a series The concept of per cent transmittance (%TI is introduced, and stuof demonstrations showing the conversion of solid to liquid (ice + dents are told that an IR spectrum has %T as the y-axis and cm-' water), liquid to gas (evaporation of liquid nitrogen) and solid to as the x-axis. Each student then receives IR spectra of the followgas (subli&tion of iodine). ing molecules, along with their names and structures: c. Examples of chemical change. Students in groups of two fkoctane fkbutanol ethyl butyrate or three perform experiments involving observable chemical reac1-hexene 2-propanol 2-pentanone tions. These include a reaction that generates heat and causes for1-hexyne 2-butylamine benzaldehyde mation of a precipitate (formation of Mg(OH)2 from KOH and MgS04), a reaction with a product gas (vinegar and baking soda), acetonitrile amyl acetate phenetole reactions which result in color change (iodine and HSOsand iodindstareh clock ( I ) ) , reactions producing light (light sticks) and We ask students to find patterns or spectral signatures for the a reaction that produces slime, a polymer product (2). functional groups present in these molecules, paying careful attention only to the peaks >I500 cm-'. Students are urged to use 11. Ball-and-Stick Models of Molecules (two to three classes) the n-octane spectrum a s a reference and to compare the spectra of other molecules with this spectrum to locate peaks for specific We tell students that we use ball-and-stick models to reoresent functional groups. In doing this exercise, students get the idea mnlrculnr real$ hrcnuse molecules are too small to uork w t h that IR spectra can be good functional group indicators, and they indwidually in a normal laboratory situation. To bepn, studcnts begin to assemble their version of an IR canelation chart. are givcn three rulcs to apply in building molecular models: mly Students, in groups of two or three, are assigned three unknown the valence electrons (which is the gmup number in the periodic liquids from the list below and asked to obtain IR spectra on each table for C, H, 0 , N, Cl and Br) are involved in bonding, a chemical of their unknowns. Each student receives a list of the names and hand can be viewed as a shared electron pair, and the valence elecstructures of the 12 molecules listed, trons about an atom end up as either bonding or nonbonding pairs in a molecule. Students start with models of alkanes and then go 2-hexanol 2-butanol benzyl alcohol onto molecules containingother elements (HzO,NH,, CCI,). They 1-octene acetophenone Phexanone eventually arrive at the following table for molecules containing salicylaldehyde hexanal 1-pentanol these atoms: hexanenitrile butyl acetate benzylamine Element #of bonds #of nonbonding pairs During the next class period, each group reports orally to the rest of the class on the oossible identitv of each of their unknowns. Ambiguities using only IR (Phexanol versus 2-butanal?) are reN 3 salved by having students obtain a mass spectrum. In this way, 0 2 students begin & realize the powerful benefit that accrues from 1 CI. Br using more than one technique to determine molecular structure. ~~
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At this point, when students have already taken and interpreted IR spectra, we discuss the origin of these spectra. After intraducing the concept of quantized energy levels a t molecular dimensions, we point out that the bonds in our ball-and-stick models are really more like vibrating springs than rigid sticks. The MolVib program from Journal of Chemiml EducatLon: Software (D. Huber) is used to simulate stretching and bending vibrations for H 2 0 and CH4 and the effect of mass on stretching frequency using H20 versus HOD. Other concepts that we either state or show by example indude the fact that absorption occurs when the natural mode frequency and that of the incoming IR radiation coincide, the relation of bond type (single, double, triple) to stretching frequency, and the division of the IR region primarip into h c t i o n a l group (>I500 cm-'1 and fingerprint (
