[1]
Purpose
To help the teacher and students be aware of students’ initial thinking about the particle nature of matter and what happens during evaporation.
Description
Present students with the following scenario: A family takes their dog to the park for several hours on a hot, sunny day. The dog’s water bowl is left outside in the backyard while they are gone. Ask students to predict what will happen to the water in the bowl over time. (They should predict that the amount of water will decrease or disappear completely.) Next, ask them to imagine that they have super strong glasses [2] that are more powerful than the strongest microscope (Loughran, Mulhall, & Berry, 2004; Prain et al., 2009) [3]. Then ask them to draw a picture that illustrates what they see happening to the water in the bowl using this task sheet [4]. [Task instructions for pilot teachers. [5]]
Questions to Ask Students
- Describe what’s in your drawings. What does each part represent?
- How does your drawing explain what is happening to the water in the bowl?
- If any students predict the water in the bowl will evaporate, ask them to describe what evaporation means.
Student Thinking
- Some students’ drawings will represent water as continuous (that is, they will not draw water particles), even in the vapor phase (Benson, Wittrock, & Baur, 1993; Nakhleh & Samarapungavan, 1999; Renström, Andersson, & Marton, 1990; Séré, 1986) [3]. If students draw particles, look for:
- Size and shape of particles in different states. Some students believe size and shape change as the states change (Aydeniz & Kotowski, 2012; Özmen, 2011; Özmen & Kenan, 2007; Tsai, 1999) [6]. For example, some think water particles are bigger in the vapor phase than the solid phase.
- Number of particles. Some students believe that the particles disappear (literally cease to exist) when water evaporates (Lee, Eichinger, Anderson, Berkheimer, & Blakeslee, 1993; Osborne & Cosgrove, 1983; Russell et al., 1989; Tytler, 2000) [6].
- Just because students use the words “evaporation” or “evaporate” when predicting what will happen to the water, don’t assume they know what the words mean. Ask students to explain what they mean by those words, but do not correct their ideas at this point.
Implementation Tips
- Encourage students to write their predictions in their science notebook or in some other place that they can refer back to as their thinking evolves.
- The drawings will help the teacher understand what students think about matter at this point in the pathway and be alert for opportunities for students to challenge their thinking.
- Collect and keep the drawings, or ask students to keep the drawings (for example, in their science notebook), so they will be able to compare their thinking at this point with their thinking at the end of this driving question pathway.