Reports on a study aimed at facilitating freshman general chemistry students' understanding of atomic structure based on the work of Thomson, Rutherford, and Bohr. Hypothesizes that classroom discussions based on arguments/counterarguments of the heuristic principles on which these scientists based their atomic models can facilitate students' conceptual understanding. Concludes that with argument and discussion, students' understanding can go beyond the simple regurgitation of experimental details. (Author/MM)