Some of us use drawings, models, or a variety of different types of molecular dynamics simulators to try to model this invisible side of chemistry. Is it worth the time and effort? A recent research report, "The Effects of Computer Animation on the Particulate Mental Models of College Chemistry Students" by Vickie Williamson and Michael Abraham, suggests that animations may be. The report is published in the Journal of Research in Science Teaching 1995, 32, 521-534.

Williamson and Abraham worked with three groups of students in a university general chemistry class: a control group taught using the blackboard and static transparencies and two treatment groups, one that also viewed a presentation of computer animations of particulate behavior as a visual aid in lectures, and a second group that also viewed the animations in lecture and as an assigned activity during a discussion session. The three groups were determined to be equivalent before the start of the experiment. Following the experiment no differences in attitude towards instruction in the course were detected; in other words, the students in the treatment sections felt neither special nor "picked on"

The animations were used with a unit on the properties of gases, liquids, and solids and with a unit on chemical reactions. Each unit was approximately two weeks (four lectures) in length and the animations constituted about five percent of the lecture time. Following each unit each student's conceptual understanding was determined using a standard measure, the Particulate Nature of Matter Evaluation Test (PNMET). Exam scores were also used in the evaluation.

It was found that students who viewed the animated sequences depicting particulate behavior exhibited a significant increase in their level of conceptual understanding of the behavior of matter at the molecular level, as determined by the PNMET, compared to students in the control section. However, the improvement did not extend to algorithmic (rote, number-crunching) exercises on the course exams. Interestingly, more did not seem to be better in this case: both treatment groups performed equivalently. Students in both groups viewing the animations were found to have fewer misconceptions regarding properties of gases, liquids, and solids and reaction chemistry, the two units covered in the study. It was also found that these students held a more particulate view of matter. These observations suggest that animations may increase conceptual understanding by prompting or providing mental models of the microscopic phenomena.

That the improvement did not extend to traditional algorithmic (rote, number-crunching) exercises on the course exams is an interesting finding. It suggests students can pass traditional chemistry courses with little understanding of the microscopic world.