States of Matter — solid, liquid and gas — are explained by the particle model.
In a solid, particles are packed tightly and vibrate in place. In a liquid they are close but can move. In a gas they are far apart and move quickly. Changes of state include melting, freezing, evaporation/boiling and condensation.
Remember
- Three states: solid, liquid, gas.
- Melt: solid→liquid · Boil/evaporate: liquid→gas.