In this section, we delve into the basic classification of matter into three states: solids, liquids, and gases. Each state is defined by unique properties that arise from the arrangement and movement of particles. Solids possess a definite shape and volume due to tightly packed particles held together by strong forces of attraction. Liquids have a fixed volume but take the shape of their container, with particles that are less tightly packed and can move past one another. Gases have neither a definite shape nor volume and fill the available space as their particles spread out due to weak intermolecular forces and high kinetic energy. The chapter emphasizes the importance of temperature and pressure in determining the state of matter, including processes like melting, freezing, evaporation, condensation, sublimation, and deposition.