Students observe and discuss water on the molecular level using the idea that water is composed of tiny molecules that are attracted to one another.

One way scientists talk about matter or substance-that is, the stuff in the world-is in terms of pure substances and mixtures. Pure substances are substances that contain only one kind of molecule. Water with nothing else in it is a pure...

Students investigate how low temperature causes water vapor to condense into a liquid and then freeze to form a solid.