Chapter 3 · Matter and Energy
3.2What Is Matter?
8 min · two checks
Predict
What do solids, liquids, and gases have in common at the particle level?
The idea
- Describe particle motion in solids, liquids, and gases.
- Connect the definition of matter to particles.
Matter is made of particles — atoms, molecules, or ions — and those particles are always moving. In a solid they vibrate in place inside a fixed arrangement, so the solid keeps its shape. In a liquid they stay close but can slide, so a liquid takes the shape of the container and keeps its volume. In a gas they are far apart and move in straight lines until they collide, so a gas fills whatever volume it is given.
Between the particles of a gas there is empty space, not “air.” Air is itself a mixture of gas particles. Compressing a gas mostly reduces that space, which is why gases are compressible and liquids and solids mostly are not. Temperature, in a later section, will turn out to be a measure of how vigorous this motion is.
Keep these
- Particles are in motion in every state.
- Solids: fixed arrangement. Liquids: contact but mobile. Gases: far apart.
- Gases are compressible because of the space between particles.