Final answer:
The states of matter refer to the distinct forms matter takes on, primarily solid, liquid, and gas, with particles in these states displaying different arrangements and energies. A fourth state, plasma, is recognized in physics. Changes between these states are driven by variations in thermal energy and explained by kinetic molecular theory.
Step-by-step explanation:
The states of matter are the distinct forms that different phases of matter take on. Historically, matter is identified to exist in mainly three forms: solid, liquid, and gas. A solid maintains a fixed volume and shape with tightly packed particles that are fixed in place. A liquid also maintains a fixed volume but adapts its shape to fit whatever container it occupies, with particles that are close together but move freely. A gas has variable volume and shape, filling the entirety of the container it is in, and its particles are far apart and move randomly. There is also a fourth state known as plasma, which is not as common in everyday life but is essential in physics for understanding behaviors under extreme energy conditions. Matter undergoes phase changes from one state to another through the process of heating and cooling, which affects the energy of the molecules. Kinetic molecular theory helps to explain the differences in properties between the states of matter, such as boiling points and melting points, by looking at the movement and energy of the particles.