edited by: RON DELORENZO Middle Georgia College Cochran. Georgia 31014
Bowling Balls and Beads: A Concrete Analogy to the Rutherford Experiment Mary V. Lorenz Noire Dame Academy Hilton Drive Park Hills. KY 41011
Many beginning chemistry students do not comprehend the Rutherford experiment. One reason for this is that they do not have an intuitive understanding of what happens when a particle in motion hits a stationary particle of significantly different mass. T o simulate this experience on a macroscopic level several spheres can be used to represent the microscopic particles of the atom in a bombardment demonstration. Spheres are selected that approximate the mass ratio of the microscopic particles. A bowling ball is used to represent the nucleus; a softball, the alpha particle; a rackethall, the proton; and a small bead, the electron. The demonstration does not address the electrostatic repulsion present in the Rutherford experiment. This phenomenon is presented in the ensuing classroom discussion. The students are encouraged to explore in small groups or by class demonstration what happens when a softball (alpha particle) is rolled at the other stationary spheres, one at a time. The students can see in which cases the path of the softball is altered significantly by the resting sphere, and they can deduce the effect of the mass ratio of the spheres on
1082
Journal of Chemical Education
this nhenomenon Thompson's plum pudding model, which features isolated nrotonsnnd electrons. can be iesred hv rollinr! the soitball at the rackethall (protoh) and bead (eiectron): A model that proposes a combination of microscopic particles in a nucleus can he analyzed by rolling the softball a t a bowling hall. The demonstration can serve to show why certain models of the atom, such as the plum pudding model, are incorrect. A computer simulation of the Rutherford experiment (SERAPHIM Program AP204, Side 1) can be used in conjunction with this demonstration. The animation in the program gives the students a clearer impression of what is occurring in the experiment. I t provides an approximation of the number of particles that went through the foil vs. the number that were deflected. The demonstration and computer simulation can be used as background for a discovery exercise in which the students predict the model of the atom from Rutherford's data. (An updated version of this simulation, called "Alpha Scatter", is available in Volume IA, Number 1of JCE: Software.) The relationship between the size of the microscopic particles and the size of the atom can he put in perspective by using a traditional analogy of the collisions occurring in the Houston Astrodome. The howling hall is a t the center of the field and the softball is launched from the stands while the bead could he anywhere in the stadium. The students seem to understand this analogy better after seeing or participating in the macroscopic collision experiment in the classroom.
