Particulate Level Conceptual Questions

The picture posted here is one example of a formative assessment that I have seen as part of many activities (including an article published in JCE) and that I use in class. I set a beaker of water on a hot plate to boil. There is a large beaker above the water (a sheet of glass would also work). I don’t tell the students that the beaker has water in it. Instead, I tell them that the beaker contains a pure solution made of equal parts element A and element B. They are instructed to create a key for the symbols they use to represent each element. I ask them to draw three circles on the paper that will each zoom into a specific point in the set up to provide a particulate level model of what is happening at each location. The bottom circle will represent what the liquid compound units look like within the beaker. The middle circle will represent the gas phase of those same units and the top circle will represent what is happening on the bottom surface of the upper beaker. After allowing a few minutes to complete the drawings, I ask the students to share their drawings with others at their table and discuss. They may decide to modify their drawings. I then ask a few students to share their drawings in front of the class and explain/defend what they show us. I don’t immediately point out errors. I ask students to save comments until we have a chance to view several drawings. I then ask the students to write down comments about each before we discuss. If necessary, I create my own models to encourage discussion about which models are the best. We focus more on revising models to make them better than picking apart the negative aspects of any particular model.