Creative Student-Made Molecular Models Gordon L. Eggleton, John J. Williamson, Cherry E. Loveless, and Bradley C. Grimes Southeastern Oklahoma State University, OK 74701 Portraying basic geometrical shapes of molecules to introductory chemistry students is both important and difficult. The construction of models is a useful laboratory activity for defining such shapes in the minds of beginning students. Commercial ball-and-stick models, while convenient, are limited bv their exnense and amount of student partici~ation in determining hond angles, relative size of atoms, and color codes to he used. Another option. Styrofoam hall mod. els' can also he expensive ($0.6Rlsrudent) and restrict arudent participation in determining the relative size of atoms without the use ofa difficult proredure:. A student attempting to translate from a two-dimensional figure to a threedimensional model should he required to choose appropriate nires and spacial relationships of the atoms in the species. In our laboratory students prepare permanent models from cotton balk and glue as shown in the illustration. The models are cdorful. inexoensive ($0.08/studentl. allow student participation in all aspects of the final product, and maintain all the advantages of conventional space-filling models. All of the materials needed, cotton balls or equivalent, white water-base glue, food coloring, and paper plates, may be purchased from local merchants. The only other e a u i ~ m e n needed t in the laboratory are heat lamps or a drying oven; for fast results a microwave oven can be used. Groups consisting of three students each are assigned to write Lewis strurtures for thespecies in one of theseven sers shown in the table. Using the VSEPR concept they assign an appropriate geometry to each species. Next they decide on a color code for each element and a relative scale of sire for their "atoms" based on oosition in the oeriodic table. Each individual "atom" is prepared before they are assembled into molecules. For each atom in the structure, a cotton ball (or a portion of one) is soaked in white glueto which mav he added several drops of food coloring. The cotton bail is saturated with coloied glue, squeezed-to remove excess glue, and formed with slightly moistened fingers into a spgerel The individual "ato&s" &e dried under a heat lamp or in an oven until the outer surface of each "atom" has a slightly hardened crust. The molecule may
then be assembled from the individual "atoms" by adding a d r o of ~ elue to hold them together in the selected geometry. ~ h k tni e glue has set, the thoroughly dried assembly is a hard, durable, colorful model. The instructor must take the lead in this "crafty" activity to establish an uninhibited atmosphere of creativity. In this setting, the students feel free to work out in their minds the relationships between the cotton balllglue models in their hands and the symbol/lines figures on the page. Allowing a student to make decisions on color, shapes, and size gives the to observe how the student perinstructor ..~..~ an oooortunitv . ceives rhe three-dimensional nature of the molecules and to helo the~student connect the symbolic Lewis strurturey with ~ appropriate models and mental images of space filling shapes for chemical species. ~~~~
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Species for Student Models A
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' Pierce, J. B. J. Chern. Educ. 1959 36.595.
Kenney, M. E. J. Chem. Educ. 1958 35.513,
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Journal of Chemical Education
Variety of models made from conon balls and glue.
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