564
JOURNAL OF CHEMICAL EDUCATION
A SODIUM ATOM MODEL FOR LECTURE DEMONSTRATION GEORGE A. HALL, JR. University of Wisconsin. Madison, Wisconsin
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BEGINNING chemistry student often gains an erroneous, if not to say bizarre, impression of atomic structure from the conventional two dimensional, concentric circle diagrams given in most texts. A re* souably accurate three-diniensional model of one of the lighter atoms would greatly assist the visualization of the modem concept of the atom. Such a model for highschool instruction has recently been described.' At the college level, however, it should be possible to present the students with a more complete and more accurate model. It is obviously impossible, and also highly undesirable from the point of view of the teacher of beginning chemistry, to construct a physical model embodying the com~leteauantum mechanical theory of atomic structure: the ~ohr-~ommerfeld theory does lend itself well t o the construction of scale models of the simpler atoms. While not strictly rigorous this model does show as many of the theoretical concepts as the beginning student can readily uderstand. The niodel shown in the figure was mnstructed using the fundamental equations of the Bohr-Sommerfeld treatment.= The sodium atom was selected since it is large enough to illustrate all of the important features and yet is small enough t o avoid complexity. The K orbit is a circle of four inch diameter. The L orbits are three circles of 16 inch diameter and one ellipse of 16 inch major axis and eight inch minor axis. These orbits inch steel wire. The M orbit is an were made of ellipse of 36 inch major axis and 12 inch minor axis constructed of a / , ~ inch brass rod. The electrons were made of one-half inch brass rod, two inches long, machined to a gradual taper from the full size down to the size of the central hole for the wire orbits. Two electrons were mounted on each orbit, except for the last. This was considered the most satisfactory arrangement since there is no method of representing the difference BROOKS, W. O., THISJOURNAL, 24,245 (1947). 'PAUIJNG,L., AND E. B. WILSON, JR., "Introduction to Quantum Mechanics," MeGraw-Hill Book Company, New York,
ow ever
1936, pp. 3&47.
Sodium Atom Model
in the spin of the electrons and since a larger number of orbits would reduce the clarity of the model. The electrons and the part of the orbits nearest the "tail" of the electrons were painted white, while the rest of the orbit is black with dashes of white. The tapered shape of the electron and the painted orbit convey some idea of motion. On the above scale the nucleus should be of the order of 0.0001 inch in diameter but was made a one-inch sphere, painted red and white for reasonable visibility. The orbits were soldered to a wire cross piece which is painted black and passes through the nucleus. The spatial orientation of the orhits was based on purely esthetic considerations. When accompanied hy some explanatory remarks in the lecture about the actual size of the nucleus, the nature of electrons, and the dynamic nature of the whole system, this model has been quite successful in our general chemistry lectures. It has apparently stimulated some thinking on the part of the students and has given rise to a large number of interesting questions. The author would like to gratefully acknowledge the assistance of Mr. 0. A. Talliaferro who constructed the model and Mr. Richard Livesay who photographed it.
