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The Properties of Water | ||
| Issue | Naive Idea* | Scientific Idea |
| Structure of Water | Water has H20 molecules in it, with water between the molecules. | All water, ice and water vapor is made of H20 molecules which contain empty space and are surrounded by empty space. The electrons are in constant motion and some H2O molecules in water ionize to form H30+ and OH-. |
| Size of Water Molecules | Water molecules are similar to cells or dust specks. Water molecules can be seen with microscopes. | Water molecules are too small to see even with the most powerful microscope. |
| States of Water | Water molecules share properties with observable states of matter. Thus water molecules in liquid form are thought of as liquid themselves. | The state of a substance (solid, liquid, or gas) derives entirely from the way in which the molecules are organized in that substance. The molecules do not change, but the interactions between them do. In liquids like water, molecules move freely, slipping and sliding past one another. At the same time, the molecules bind together and the substance takes on the shape of its container, seeking the lowest level. |
| Dissolving | Substances change into new substances when they dissolve. | Dissolving involves the dismantling of a substance into its individual molecules which then become suspended in water. The molecules may ionize (break into charged parts), but otherwise retain their original structure and characteristics. |
| Mechanism | To name a process is to explain it - as in "Sugar dissolves in water." | A process should be accounted for by known forces in nature, in biology typically at the molecular level, as in "Sugar dissolves by dispersal of polar sugar molecules among polar water molecules." |
* This table has been adapted from Berkheimer, G. D., Anderson, C. W., Lee, O. and Blakeslee, T. D. with assistance from Eichinger, D. and Sands, K., Occasional Paper #121: Matter and Molecules Teacher's Guide: Science Book. We are indebted to the authors for both their information about alternative conceptions and for their idea of a 'conceptual contrasts' table, which we will refer to as 'Alternative Ideas.'
Alternative ideas are known by many names including alternative conceptions, misconceptions, and naive ideas. They have been extensively studied during the past 15 years. These alternative ideas are shared by a significant fraction of the population of students, often 20-60% of students in a class, they are surprisingly resistant to being taught away (especially with traditional, didactic teaching), and while some alternative ideas are culturally bound, most appear in similar frequencies in classrooms around the world.
This does not imply that all prior knowledge is faulty. Students have had valuable experiences with water, for example, all their lives. A good teacher will draw out some of those experiences and link them to events in this lab. Scientific understanding is strengthened when it is integrated with everyday knowledge.
