Solids, Liquids and Gases

All matter is made up of tiny particles. These particles are much too small to see.

These particles are arranged differently in solids, liquids and gases.

Explaining changes of state from particle theory.

Heating solids

When solids are heated, they expand. The particles in solids are arranged in a fixed pattern.

The particles are held together strongly and tightly packed.

The particles in the solid vibrate. The heat energy is transferred to the particles.

The more energy the particles have, the more they vibrate. As the particles vibrate more, they take up more space.

The particles are still held in position by the attractive forces between them.

Melting solids

When solids are heated even more strongly they melt. They become liquid.

The particles in the solid vibrate more and more as heat energy is transferred to them.

The particles vibrate so much that the attractive forces between them are no longer strong enough to hold them in a strong enough to hold them in a fixed pattern.

They are able to slide past one another. The forces are still strong enough for the particles to stay in touch with one another.

The more the liquid is heated, the more energy is transferred to the particles and the more the particles move.

Boiling liquids

When liquids are heated they evaporate and eventually boil. In liquids the particles touch each other. The particles are held together weakly.

The particles move more as heat energy is transferred to them.

Some particles have enough energy to break the weak attractive forces holding them together.

These particles can escape into the air as gas particles.

Cooling gases

The particles in a gas are free to move anywhere and spread out. There are no forces holding them.

When a gas gets cooler it condenses to form a liquid. When gas particles reach a cold surface, some of the heat energy transfers from the particles to the surface.

The particles move less and get closer together. They form a liquid.

Freezing liquids

When a liquid freezes it becomes a solid.

The particles in a liquid move and slide past each other.

As heat energy is transferred from the particles to the environment, the particles move, more slowly and the liquid gets cooler.

The cooler the liquid is, the less the particles are able to move or slide past each other.

Eventually the particles have so little energy they can only vibrate.They become arranged in a fixed pattern to form a solid.