AC 2010-1263: STUDENT UNDERSTANDING OF ATOMIC BONDS AND THEIR RELATION TO MECHANICAL PROPERTIES OF METALS IN AN INTRODUCTORY MATERIALS SCIENCE ENGINEERING COURSE

We report on initial findings of a project to identify, study, and address student difficulties in a university-level introductory materials science course for engineers. Through interviews of over 80 students and testing of over 300 students, we examined in detail student understanding of the atomic bonding and mechanical properties of metals. Here we describe a number of student difficulties in understanding atomic bonding and its relation to macroscopic properties of metals. For example, students often confuse density, strength of atomic bonds, melting temperature, and yield strength. Many students also believe that when the temperature of a metal bar is increased, the metal expands “because the atoms are moving faster and need more room”. Students also often believe that bonds themselves can be permanently weakened or stretched, and they often confuse bond strength with force rather than energy. All of these results were obtained after traditional instruction that explicitly covered these topics. We describe active learning group-work lessons aimed at improving student understanding of atomic bonding which are similar in structure and style to lessons shown to be effective in physics education research efforts. Students were presented with an asymmetric atomic bonding potential energy curve and a symmetric potential energy curve for a “ball and spring” model of atomic bonding. They were then asked a series of questions comparing the behavior of the atoms in the two cases. This lesson was pilot tested in recitation sections, and we found students to be actively engaged in the exercises. At the end of the session students were able to explain on an atomic level why a metal expands when heated, the origin of elasticity of metals and why melting occurs when the temperature reaches a critical level. Previously, most students could not provide these explanations after traditional instruction.