The study explores the roles of instructional animation to support middle school students' learning of chemistry concepts. We discuss two roles of animations: a constructivist tool to support visualization and interpretation of chemical processes, and a problem-solving tool to support reasoning about chemical phenomena. We developed Chemation, a handheld-based chemistry animation tool, to address the roles. We conducted an initial evaluation study to assess the impact of Chemation for supporting students' visualization, interpretation, and reasoning of chemical phenomena. Two teachers and 73 seventh grade students participated in the study. The results of pre- and posttests indicated a positive gross effect of the learning environment including all aspects such as teacher and tool supports. Close examination through classroom observations, student interviews, and student artifacts revealed the relationships between student learning and tool supports. The results inform the design of interactive learning environments that incorporate animation as a learning support.