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# Subject knowledge: The Particle Model

All matter is made up of particles and although an understanding of particles is not a requirement at the primary level, it does help to have a firm understanding of the nature of matter to help explain the way in which materials behave.

The arrangement and movement of particles within a substance is described by the particle model.

When a material is in a solid state there are strong forces of attraction between the particles which hold them together in a tightly packed form. The individual particles are only able to vibrate in a fixed position and therefore a solid holds a fixed shape and volume. Imagine a layer from a nice box of chocolates with marbles in each hole. If you shake the trays the marbles can vibrate but not move from their assigned position.

The forces of attraction between the particles in a liquid are weaker than in a solid and are able to move with more freedom. This makes substances slightly less dense when they are a liquid than when they are a solid. It will have a fixed volume but not hold a fixed shape. One thing we know about liquids is that they take the shape of the container they are poured in. A good analogy for this would be balls in a ball pool. They can move freely around but will keep the same volume of balls and fill the pool.

Within a gas the forces of attraction between the particles are very weak and they move independently of each other. They move randomly and a gas has neither a fixed shape or volume. You can easily compress a gas. This is much more difficult to imagine but you can think of it as like a tombola or bingo machine with lots of balls flying about inside, independent of each other.

If you would like to extend your understanding of the particle model, refer to BEST Evidence in Science Teaching.

## Compare

How did your diagrams from the last step compare to the ones here?

Did you notice that the particles in the liquid and solid are still as closely packed? The liquid particles are able to move more freely but they don’t get further apart.

Did you also notice there are the same number of particles in each diagram? This is to avoid misconceptions of particles disappearing.

Comment below to let us know how you got on. Did your depictions agree with the ones above or were any surprising differences?