Students are introduced to the idea that matter is composed of atoms and molecules that are ... molecules as they experiment with and observe the heating and cooling of a solid, liquid, and gas.

changing from a solid to a liquid, for example. This basic model is, however, just that: there are many, many more states of matter out there that it doesn’t capture. The next most familiar is ...

Matter is the "stuff ... Most substances can exist as a solid, liquid or gas. They can change state, usually when they are heated or cooled. For example, liquid water turns into water vapour ...