Key points

  • Substances can exist in three states of matter - solid, liquid and gas.

  • All substances are made from particles, and the forces between the particles are different in solids, liquids and gases.

  • The arrangement, movement and spacing of the particles explain many of the properties of solids, liquids and gases.

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Video

Watch this video to see a model of how are arranged in solids, liquids and gases.

Describe the arrangement and movement of the particles in a solid, liquid and gas.

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Solids

Lots of materials are solid, such as paper, bricks, wood, metal and ice.

There are strong forces between the in a solid which hold the particles in fixed positions, in a regular arrangement. The particles are close together and vibrate about these fixed positions. They cannot move from place to place.

Because the particles are in fixed positions, solids have a fixed shape and cannot flow like or . There is very little space between the particles in solids, so they cannot usually be .

When drawing the particles in a solid, they should be closely spaced, in neat, ordered rows.

An infographic showing particles in a solid, which are closely packed together
Figure caption,
The particles in a solid are closely spaced and arranged in neat, ordered rows. The particles are held in place by strong forces but can vibrate about their fixed positions.
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Liquids

Examples of common liquids include water, oil and fruit juice.

The between the in a are weaker than the forces between particles in a , so the particles are not held in fixed positions.

The particles in a liquid are still close together, like the particles in a solid, but are arranged randomly. As well as vibrating, the particles in a liquid can move from place to place.

Because the particles are not in fixed positions and can move about and vibrate, liquids do not have a fixed shape and can flow. This means that a liquid will take the shape of the bottom of its container. Like a solid, there is very little space between the particles in liquids, so they cannot usually be .

When drawing the particles in a liquid, they should be closely spaced with very few gaps, in a random arrangement.

An infographic showing particles in a liquid, which are arranged randomly with some space to move around
Figure caption,
The particles in a liquid are closely spaced and randomly arranged. The forces holding the particles are weaker than in a solid so, as well as vibrating, the particles can move from their fixed positions.
Milk being poured into a cup of tea

Liquids and gases are both examples of . They can both flow, and some gases can even be poured, like a liquid.

Milk being poured into a cup of tea
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Gases

There are lots of different including:

  • the air we breathe

  • the steam produced when a kettle boils

  • the helium used to fill balloons.

The in a gas have enough to overcome the attractive that try to hold them together. Because of this, the particles in a gas are widely spaced and free to move in any direction. The particles in a gas do not vibrate - instead they move quickly in straight lines, in random directions. This means the particles can collide with each other and with the walls of any container present.

Because the particles in a gas can move freely in all directions, gases do not have a fixed shape. They can expand to fill their container and flow to take its shape. Gases can also be easily because there is lots of space between the particles.

When drawing the particles in a gas, they should be widely spaced and in a random arrangement

An infographic showing particles in a gas, which are randomly arranged with lots of space between them, each particle moving in a random direction
Figure caption,
The particles in a gas are widely spaced and randomly arranged. The particles move quickly in random directions, at random speeds.
Cylinders containing compressed gas being transported by a truck
Image caption,
Oxygen is compressed before being transported to hospitals, so it takes up less space.

If a gas is compressed to a very high pressure, it can become a .

Gases are often compressed before being transported, so they take up less space.

Cylinders containing compressed gas being transported by a truck
Image caption,
Oxygen is compressed before being transported to hospitals, so it takes up less space.
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Working safely in the lab

Find out how to spot risks, hazards and understand hazard symbols

Working safely in the lab
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