ABSTRACT
In everyday contexts, we heat water to make tea or melt chocolate to cover a cake. Puddles on the pavement dry up in the sunshine and water turns into ice cubes in the freezer. The words that we use to describe what we observe, such as solidifying, melting, boiling and condensing, label these events in scientific terms but give no explanation of the processes taking place. In order to help to explain why materials such as water change their properties when they change from a solid to a liquid and to a gas, we need to offer a story or a model which will help in visualising the processes involved. This chapter explores the particle nature of matter and how this can be used to make sense of phenomena such as ice cubes melting and sugar dissolving in water.
