Kinetic Theory of Matter
The Particle Model of Matter · Kinetic Energy and Temperature · Applying the Kinetic Theory to Everyday Phenomena
IB Chemistry topic guide
Structure 1: Particulate Nature
Structure 1: Particulate Nature is a core part of IB Chemistry. This guide connects the syllabus ideas behind Kinetic Theory of Matter, Changes of State, Gas Behaviour and Diffusion, Atomic Structure and Isotopes, Mass Spectrometry and Atomic Models and 4 more units, shows how they appear in worked problems, and points you to the formulas and full lessons needed for exam revision.
What you will learn
Structure 1: Particulate Nature syllabus outline
The units below follow the structure used in the full Study to Learn course. Use the outline to identify exactly which idea needs attention, then work through the public example before continuing to the complete lesson path.
Changes of State
Melting, Boiling, and Sublimation · Heating Curves and Latent Heat
Gas Behaviour and Diffusion
Properties of Gases · Diffusion and Brownian Motion
Atomic Structure and Isotopes
Inside the Atom: Protons, Neutrons, and Electrons · Isotopes and Relative Atomic Mass
Mass Spectrometry and Atomic Models
The Mass Spectrometer · Historical Development of Atomic Models
Energy Levels and Orbitals
Shells, Subshells, and Orbitals · The Periodic Table as an Electron Configuration Map
Ionisation Energy
Definition and Successive Ionisation Energies · Trends and Irregularities in First Ionisation Energy
The Mole Concept
Counting Particles by Mass · Concentration, Dilution, and Reacting Quantities
Ideal Gases
The Ideal Gas Law · Why Real Gases Aren’t Quite Ideal
Free worked preview
The Particle Model of Matter
This complete preview comes from the Kinetic Theory of Matter unit. It introduces the core language, shows the method in context, and gives you a real example of the lesson quality before you create an account.
What Matter Is Made Of
Everything you see around you — from the chair you sit on to the air you breathe — is made of particles so small you cannot see them. This lesson is the starting point for the entire IB Chemistry course: it explains how the three states of matter arise from different particle arrangements and movement patterns, and why gases, liquids, and solids behave so differently. When you finish, you will understand that all matter consists of particles in constant motion, and you will be able to connect macroscopic observations (why a solid holds its shape, why a gas expands) to the invisible world of atoms and molecules.
All matter is composed of tiny particles (atoms, molecules, or ions) in constant, random motion. The arrangement and motion of these particles determine the physical state of a substance — this is the foundation of the kinetic particle theory.
Three States of Matter
- Solid: particles are tightly packed in a fixed, regular arrangement; they vibrate in place about fixed positions; definite shape and volume; very low compressibility
- Liquid: particles are close together but not in fixed positions; they can slide past each other; definite volume but take the shape of their container; low compressibility
- Gas: particles are far apart, moving rapidly and randomly in straight lines until they collide; no definite shape or volume; highly compressible; exert pressure through collisions with container walls
Evidence for the Particle Model
The particle model is not just assumed — it makes testable predictions confirmed by experiment. Compressing a gas reduces its volume and increases its pressure (more frequent collisions); heating a solid eventually turns it into a liquid, then a gas, as added energy overcomes progressively stronger attractive forces between particles; the fixed shape of crystals reflects the regular, repeating arrangement of particles at the microscopic level.
Common ErrorThe particle model describes bulk behaviour of matter at the macroscopic level and explains observable properties (e.g. why liquids flow, why gases are compressible). Do not confuse “particle” in this context with subatomic particles (protons, neutrons, electrons) — the kinetic theory deals with atoms, molecules, or ions as whole units.
Reviewed by the Study to Learn editorial team · Updated 2026-08-04