This document discusses the phases of matter (solid, liquid, gas) and phase changes. It explains that: - Gases have molecules that are spread far apart and hold a lot of energy. Elements and compounds can change phases when certain conditions are present. - When the melting point is reached, a substance becomes a liquid. Melting sugar is a physical change because it is still sugar. - Scientists use a thermometer to measure when a liquid turns into a solid. Plasmas are like gases but have free electrons and ions. Atoms in solids cannot move around much. - Tables show the microscopic explanations for behaviors of gases, liquids and solids like compressibility, ability to