The document discusses the three states of matter: solid, liquid, and gas. It explains that solids have molecules that are closely arranged with strong attractive forces, while liquids have molecules farther apart with more freedom of movement, and gases have molecules that are far apart with weak attractive forces. The document also notes that increasing heat energy can change a substance from one state to another, and it compares how solids, liquids, and gases differ in terms of compressibility and diffusion. Examples are provided for each state of matter.