Particle model
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Why
Why does water flow, but a stone does not? Why does air fill a whole room? We cannot see the smallest parts of substances. With a model we imagine them and use it to explain what we observe.
Rule
- Particle model
In the particle model every substance consists of very small particles, which you imagine as balls.
| State | Arrangement of the particles | Movement |
|---|---|---|
| solid | close together, in order | vibrate in place |
| liquid | close together, not in order | change places |
| gaseous | far apart | move freely through the space |
When a substance gets warmer, its particles move faster. With enough heat they break out of their fixed order: the substance melts. With even more heat they fly apart: the substance boils.
Example
Water is heated
Ice is solid. The water particles sit close together. At 0 °C it melts, then they are mobile and the water flows. At 100 °C it boils: the particles fly apart and it is water vapour.
solid: The particles sit close together and vibrate in place.
A box with 30 particles and a slider for the temperature. At a low temperature (solid) the particles sit close together and vibrate in place. At a medium temperature (liquid) they are close together and change places. At a high temperature (gaseous) they are far apart and move freely through the whole box.
Practice
Exercise
Solution
Right answer: solid – particles close together, vibrate in place; liquid – particles close together, change places; gaseous – particles far apart, free to move
The higher the temperature, the more mobile the particles. In the solid state they have fixed places, in the liquid state they change places, in the gaseous state they fly freely.
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Exercise
Solution
The particles are close together but change places. right answer
In a liquid the particles touch but can slide past each other. That is why it flows.
The particles sit fixed in one place.
Particles have fixed places in a solid, for example in ice. That is why ice keeps its shape.
The particles are far apart.
Particles are far apart in a gas, for example in water vapour.
In a liquid the particles change places. That is why it takes the shape of its container and flows.
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Exercise
Solution
Right answer: The statement is false.
The particles stay the same size. They only move faster and therefore often need more room.
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