MODEL OF AN OXYGEN ATOM WILLIAM 0. BROOKS Technical High School, Springfiel& Massachusetts CoNvmwmcs as well as clarity requires us to represent the electrons and their orbits on the blackboard as concentric circles around the nucleus. Yet we realize that t,he arrangement of the electrons is not flat, saucerlike, but more nearly spherical. In order to give students a clearer idea of the probable structure of a simple atom, such as oxygen, a model was constructed of large size from heavy steel wire and colored wooden balls. .4fter painting and assembly, the model, nearly four feet in diameter, was hung from a hook in the ceiling of the classroom as a permanent display. St,eel wire of 3/1B-iu.diameter was found to he sufficiently flexible to bend into four-foot circles for the orhit,s of the elertrons of the second shell of the oxygen atom. Six pieces of appropriate length were cleaned and painted with red lead. Colored wooden balls of about 1.5-inches diameter, such as those used formolecunlar models, were used to represent the electrons. Shorter lengths of the same size wire were used to make the t,wocircles of the first shell. By piercing the wooden balls, the ends of the wire can he strung through the hole with a sufficiently tight fit t o hold the wire in a circular form. When assembled, we had two small circles and six larger circles, with a red wooden hall strung on each circle. A yellow ball was strung from the outer circles so that it was suspended in the center of the sphere. The yellow ball was used t o represent the nucleus of the atom. Fine copper wire which is invisible a few feet distant was used to hind all the circles in position. This model has been extremely helpfpl in my classes this year. There a n so many matters that come up in an elementary course that involve electronic structure that we have found this model most useful. Students have expressed a great deal of int,erest in t,he model and .
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say that it has helped t,hem to picture the struct,nrr of atoms much better than the flat, two-dimensional diagrams we are forced to use on blackboards and in texthooks. As an example of its usefulness, the quest,ion arose in class the other day, "Why does oxygen haw a valence of two?" With a pointer the teacher could show that there are only six electrons in the outer shdl of this atom and that two more are needed to make t , h ~ shell complete. The model hangs right over the ntndents' heads and is always available. I n addition, and this is a minor point, such a model hanging in the room does give a modern decorative touch to a chemistzy classroom. While any atom c m be construct;kd by similar metllods, oxygen makes a suitable model for demonstrat,iol~ purposes. It has sufficient shells and electrons t,o ronvey adequately t,he right idea, yet i t is not such a maze of balls and wires as ta confuse the students.
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