Yosuyuki Komuro and K6zb Sone Aichi Gakugei University Nagoya, Japan
Paper-made Crystal Models
Three-dimensional models of a number of simple ionic crystals can be easily constructed from a carton box of suitable size, pieces of carton paper and cellophane, adhesive tape and/or paste, and felt-point pens of blue and red colors. The mode of construction of the simplest of them, i.e., the model of an NaC1-type crystal, is shown in Figures 1 and 2. Two large windows are cut in the front and hack of the box, A , and a piece of carton paper, cut and bent, B, is fixed on the bottom of it by tape or paste. Five screens of cellophane with carton paper frames, C, are now- prepared, and the positions of anions and cations on the planes of the crystal are marked on the cellophane with felt-point pens in blue and red. All these frames are now inserted in the box, and their positions are adjusted and 6xed by the books on both sides of each screen and by the cuts of B, with which the bottoms of the screens are held. Looking through the front window of the model set up in this way, a good stereoscopic view of the relative positions of ions in the true crystal can he obtained. Models of other types of ionic crystals, such as those of CsCI, zinc hlende and fluorspar types, can also be constructed if special care is taken for their characteristic structural features. Even models of certain covalent compounds can be made; for example, a model of graphite can be obtained most easily, if the cellophane screens are identified with the planes of the hexagonal atomic "nets" in its crystal. Jn such a case, it is better to draw also the valence-bond lines on the cellophane, to make the structural features more easily perceptible. This is also true for the models of certain ionic crystals containing covalently bound particles, e.g., calcium carbide. The merits of the present model can he summarized as follows: it is very cheap and easy to make, light and portable; it is inter-convertible, so that many structures can he demonstrated with one box, because the screens in it can be exchanged quickly; space can be saved to keep many models, because many screens can
580 / Journol of Chemkol Educofion
Figure 2.
Assembled model.
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be kept together in one drawer, with only one box (or a few boxes) on the shelf. And, in some cases it also offers a possibility to take out certain important crystal planes (i.e., cellophane screens) from the crystal (i.e., box), and show them to the students separately, to give them a better understanding of the represented structure. We call this model "the aquarium model," and sometimes "the marionette theater model," too, because many amusing scenes can he played in it.
