Cambridge O Level Chemistry · Syllabus 5070 · States of Matter
Kinetic particle theory
What is Kinetic particle theory?
The model that all matter is made of very large numbers of extremely small particles that are in constant motion, and that the observable properties of a substance follow from how far apart those particles are, how they are arranged, and how they move. Increasing the temperature of a substance increases the average kinetic energy of its particles, so on average they move faster. The model explains the differences between the solid, liquid and gas states, the changes between those states, gas pressure and diffusion.
This definition is part of the States of Matter chapter in Cambridge O Level Chemistry.
Kinetic particle theory in context
States of matter are the three physical forms in which a substance can exist: solid, liquid and gas. Kinetic particle theory explains all three with one idea: matter is made of enormous numbers of tiny particles, and everything you observe about a substance follows from how far apart those particles are, how they are arranged and how they move. In a solid the particles are very close together in a regular arrangement and vibrate about fixed positions; in a liquid they are still very close together but irregular and able to move past one another; in a gas they are far apart and move rapidly and randomly in all directions.