An Innovative Use of Chemical Models

Richard V. AllensteinAssistant Professor of Chemistry, Northern Michigan University

Marquetie, Michigan 49855

Conceiving, developing and planning the utilization of three-dimensional models all offer an opportunity for a creative experienceby a teacher. This creative experience differs from the work withmodels done by Crick and Watson1 on the structure of the DNAmolecule in that the problem being attacked here has to do with in-creasing the effectiveness of teaching. While possibly deepening hisown insights into the structure of matter, the teacher can carefullyset the stage for subsequent learning by his students.As science curricula in the last decade have finally reflected the

fundamental discoveries of x-ray crystallography, science teachershave come to recognize the need to augment their verbal descriptionsof the structure of matter. But teachers have had varied success withtheir attempts at using three-dimensional models of the sort whichhad often proven useful in the original development of the concepts.Model use has proven to be very successful in remedial teaching

done on a one-to-one basis. After a teacher has diagnosed a particularstudents learning problem as one involving spatial relationships,good results have usually been obtained by prescribing a specificmodel and using it to treat the students problem.However, when confronted with today’s large classes, one of the

problems teachers encounter is the difficulty of inspiring individualinvolvement from students by the teacher’s use of small models inlecture-demonstrations. On the one hand, the models are not easilyvisible�in fact, some students could not even see the gross structure,let alone more subtle relationships built into the model. On theother hand, lecture-demonstrations are still lectures, and as suchfrequently fail to elicit active student participation.Many teachers have found value in the use of models, as reflected

in the quantity of published material dealing with models. Thispaper means to bear similar testimony to the value of models whilealso reporting some recent experiences with an innovative use ofmodels.The basic idea was to confront a large number of students first-

hand with teaching models and involve these students personally,individually with the models. To achieve this individual confronta-tion, the chemistry department borrowed the technique sometimesused in botany and zoology for laboratory testing of students by

i Watson, James D., The Double Helix, Atheneum Publishers, New York, 1968.

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An Innovative Use of Chemical Models 385

having them take turns with the models. A different model (or groupof related models) was placed at each of about two dozen differentlocations around a lab. To begin, each student went to one of thesenumbered locations where he remained by himself for a few minutes.A signal was given and all students simultaneously moved on to thenext numbered location. In this process, each student temporarilypossessed the labeled model to examine and handle at will. Motiva-tion was thereby increased, with some students being sufficientlystimulated to observe and study all the important aspects of themodel.

However, our experience had indicated that although most stu-dents are fascinated with models and some tend to respond withgreat initiative, many times the response is less than we might hopefor. In an effort to obtain a better response from a greater number ofstudents, and in order to focus each student’s attention on what we

judged to be some of the more significant aspects of each model, we

had prepared some written materials to accompany each model. Mostof these programmed-learning materials referred to features of themodel about which the student was asked questions, the answers towhich were given on separate cards. Figure 1 shows one sample ofthese materials and a picture of the actual model. In accordance withthe Skinarian approach, the students were to look at these answersfor immediate reinforcement or for correction of their own answers.

This approach was used initially in 1967, and again in the fallsemester of 1968, with our college freshman chemistry class. Some ofthe topics presented were new while some were intended for review.The response of the students was enthusiastic, with an intensity ofconcentration and involvement that was outstanding, quite like thatcommonly observed on an important examination. This responseoccurred despite the fact that the students were told beforehand thatthis was to be a strictly personal learning experience for them; theywould not be graded on their performance and written reports wouldnot be required.

Students later evaluated the approach, giving high praise for themodels over two-dimensional pictures and diagrams. Some of thesestudents criticized as inferior our previous attempts to present cer-tain topics which were reviewed at this time, even when the samemodel had been used in the earlier presentation in the large lecture,as well as in smaller study groups of about twenty. Another criticismfrom a few students was related to comments often made abouttelevised lessons, filmed courses and self-teaching written-pro-grammed courses. These students seemed to be reporting that theymissed the personal touch of their teacher. These comments mayoriginate primarily from students whose previous learning has been

386 School Science and Mathematics

FIG. 1. Typical Materials Placed at One Location

Question Card Ice Crystal Model

Answer Card

An Innovative Use of Chemical Models 387

Question Card

This is a model representing water in its solid state.1. What represents a single water molecule?2. The stick which can be easily seen connecting a white ball and a gold

ball represents what kind of bond?3. Compare the bonding distances involved in the bond mentioned in two

and the ordinary covalent bond represented in this molecule.4. Note the large open spaces within this model. What unusual property

of water is explained by the existence of these open spaces?Note that six units, each with one gold ball and two white balls form a sortof puckered ring. Two such puckered rings are marked to designate one unitcell of ice.5. How many such unit cells are represented completely in this model?6. How many HaO molecules are there in the unit cell for ice?

Answer Card

1. One gold ball (representing an oxygen atom) and the two smaller whiteballs (representing two hydrogen atoms) touching that gold ball.

2. Hydrogen bond3. Hydrogen and oxygen are bonded closer together in an ordinary co-

valent bond than in a hydrogen bond. This model exaggerates the differ-ence which in solid water is 1.1 A and 1.6 A respectively.

4. Water in the solid state occupies a larger volume than water in theliquid state.

5. Four6. 2=12Xi

essentially confined to lectures, discussions and questions from theirteacher, with little or no independent learning coming out of thelaboratory work or study of reference or text books.We allowed about half an hour for the students to return to par-

ticularly interesting or troublesome models after their initial circuitof all the models. A great deal of learning appeared to be takingplace during this last half-hour as the students engaged in enthusias-tic discussions with each other and with their teacher. The goodinteraction with the teacher at this time gave us another idea. Per-haps the idea came also from the observation that the difficulty andtime requirements varied among the different model stations andvaried among the different students. So, for the final two sections ofstudents working with the models this past year, the procedure wasmodified and the students were allowed to choose the order in whichthey viewed the models as well as the length of time they wished tostay with each one. They were also allowed to call upon the teacher

388 School Science and Mathematics

for help immediately instead of waiting until they had studied all themodels.We tried this modified procedure with a great deal of apprehension

about the possible bedlam, but the modification turned out to be agreat success! Interaction between students was positive; bottleneckswere no problem; there was less time wasted in waiting for the signalto move on to the next model; there was less frustration with runningout of time before being finished with a particular model. There wasalso more interaction with the teacher, allowing him to respond toquestions throughout the whole period instead of having them con-centrated at the end.By combining programmed-learning materials with models we

have created a technique which is not only very effective for teachingstudents individually in freshman chemistry courses, but one whichis also easily adaptable for use in other contexts. We recommend yourconsideration of this technique for further development and adapta-tion.

INSECTS AND CHOLESTEROLBiochemists have an approach which is death for specific insects but apparently

not poisonous to other animals and man. It provides an alternative to the use oftoxic pesticides. This approach could be one of the most significant breakthroughsin insect control.Two years ago the idea of using the dependency of insects upon cholesterol as a

potential method for insect control. Cholesterol is thought to be, by some, ascourge of man, an insidious fatty substance associated with clogged and hard-ened blood vessels, stroke, heart disease and high blood pressure. The substanceis made in many animals�including man�and, therefore, is not necessary intheir diet. In most insects, however, cholesterol is essential. They cannot manu-facture it, and without it, they die. It is sort of an insect vitamin. Although it hasbeen known for about two decades that insects must get cholesterol from whatthey eat in order to survive, this knowledge was not effectively used against in-sects. And the knowledge that antibiotics such as filipin block cholesterol�knowledge apparent during the last decade�had also not been effectively used tocontrol insects. As little as one part of the antibiotic called filipin to 1,000 partsof food killed or stunted the wax moth larvae. It also killed housefly larvae andhalted reproduction (egg-laying) of the adult houseflies. Often, if the particularspecies of insect survived, its growth was stunted. Filipin appears to be the mosteffective of the antibiotics tested.

Grain and vegetable crop insects are probably most susceptible to filipin.Filipin is most effective against cereal leaf beetles. The beetles can devastate en-tire fields of oats, wheat, barley and, to some extent, corn. The antibiotic mayblock cholesterol uptake in insects by combining with the cholesterol so that itcannot pass through the gut of the insect and into the haemolymph. Haemolymphis the blood of insects. If cholesterol doesn’t get to the haemolymph, then it can’tbe effectively used to keep the insect alive. The interference with cholesterol up-take affects hormone production and membrane structure. Cholesterol may bepulled out of cell membranes and cause them to leak life-supporting substances.