edited by: RON DELORENZO Middle Georgia College Cochran. Georgia 31014
The Disco Analogy Rubln Battlno Wright Sfate University Dayton. OH 45435
Students have long had difficulty in understanding the auantum mechanical model of the atom with its nrohahilitv description of the location of electrons within the atom. Students much nrefer the Bohr theorv with electrons in fixed orbits. Mv general chemistrv students resnond well to a disco anal;&. I have them imagine that they are looking down from above a t a disco dance floor. The lights are out. A lone dancer is illuminated by a strohe light that flashes once every 10 s. A photographic slide is taken a t every flash. They immediately notice that they have no way of knowing how the dancer moved from one location to another. However, if thev suaerimnose the set of slides. then thev can observe the (prohal;ility) bistrihution of the lbcation ofthe dancer. Next. the model is exoanded to include two dancers wearing hats that are unique in some way, e.g., color or size or s h a.~ e (Each .. uniaue hatldancer would revresent a uniaue set of quantum numbers-the Pauli exclusion principle.) The music is turned on and another series of photographs are taken using the strohe flashes. Superimposing the slides shows how two dancers (on a probability basis) can show the same distribution of locations that apparently have them in the same d a c e hut, of course, randomly over time. There is still no idformatioh as to what paths the dancers choose between locations.
More unique dancers can he added who somehow occupy the same space while each having individual identities and masses. (It should be added that the dancers all have the same mass!) To indicate the concent . of D. and d orhitals, it is only necessary to suggest to the students that some dancers like tomove within nrescrihed areasofthedance tloor tnand d) while other dancer(s) roam the entire floor. Thus, slides taken of a "p" dancer would when stacked show the pattern of the two-lobed p orbital with a nodal line separating them. The disco analogy also reinforces the idea that, although the dancers may he clones of each other and thus identical, they can still be unique in range of motion (energy) and identifiable by their hats (Pauli exclusion principle). The disco analogy can he expanded to include molecular orhitals. Imagine a dance floor on which you have placed two stools (representing the nuclei of atoms). There is one dancer for each stool (representing two hydrogen atoms). As the stools move closer together to some equilibrium distance, the two dancers can now move (in molecular orbitals) between and around hoth stools. The fluorine molecule may he represented as seven dancers initially each around small tables redistributing around hoth tables. Two commercially available items have helped to explain the quantum mechanical model. The first is the CHEM Study movie "The Hydrogen Atom." The movie is old, hut the analogies are illuminating. The second is a wonderful set of computer-generated electron dot-density diagrams of atoms in colorful overlays (available from SRM Inc., Janesville, WI 53545).
Volume 68 Number 4
April 1991
285
