This document discusses the four states of matter: solid, liquid, gas, and plasma. It describes the characteristics of each state in terms of how the particles are arranged and how much energy they possess. A solid has particles that are tightly packed and vibrating in a fixed position. A liquid has particles that are tightly packed but can slide over one another. A gas has particles that are very far apart and move freely. A plasma is an ionized gas where particles have high energy and behave like electricity and magnetism. Phase changes between the different states of matter are driven by increases or decreases in energy.