Guided lesson

The Three States of Matter

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2 guided lessons · 18 checks · 1. Principles of Chemistry → States of Matter

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States of matter

Everything around you exists as a solid, a liquid or a gas, and the same substance can usually move between all three. Chemists explain the differences with a particle model, picturing every particle as a small solid sphere. How those spheres are arranged, how freely they move and how much energy they hold decide which state a material takes.

What you know already

You already know from everyday life that ice melts, puddles dry out and steam fogs a cold window. This topic turns that familiar experience into a precise particle picture: what solids, liquids and gases really are, and what exactly happens when a substance changes from one state to another. By the end you will be able to name every state change and explain it through the behaviour of particles.

Key points of understanding

Solids, liquids and gases are the three states, and one substance can usually exist in each of them.
Melting and freezing happen at the melting point; boiling and condensing happen at the boiling point.
In the model, every particle is drawn as a small solid sphere, whatever the substance.
Solid particles sit in a regular arrangement, vibrating about fixed positions and very close together.
Liquid particles are randomly arranged but still close, moving around each other.
Gas particles are randomly arranged, far apart, and move quickly in all directions.

Diagram showing the regular arrangement of a solid in rows and columns — Solid — Diagram

Diagram showing how the particles in a liquid are arranged randomly and close together but not all touching — Liquid — Diagram

Diagram showing how the particles in a gas are far apart and moving quickly and randomly — Gas — Diagram

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1.States of matter

4CH1-1.1

Guided content from the SME authoring corpus — note rn_2VnK66PqbvFKdKYt, pinned at 96c261a3a06e · promoted SyllabAI/syllabai-resources e967e75f1339

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2.Interconversion Between the States of Matter

4CH1-1.2

Heat or cool a substance and it can switch between solid, liquid and gas, with a named change for each direction. Melting, boiling, evaporating, freezing, condensing and subliming all describe one underlying event: particles gaining or losing energy until their arrangement alters. Because no new substance forms at any point, every one of these changes is a physical change.

Diagram showing the changes of state — State changes require a change in the energy of the particles