Upon completion of this module, you should be able to understand the chemical composition of matter and determine whether a given substance is pure or a mixture. The matter is anything that has mass and occupies space. Matter can exist in three states: gas, liquid, and solid. Gas particles are fast-moving, are relatively far apart, and interact to a minimal extent with one another, resulting in weak interaction between the particles. Due to the distance between particles and the weak interaction between them, a gas has no defined shape and is very compressible.