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States of matter
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Solids, liquids and gases are made of the same particles. What changes is how they are arranged and how they move.
The particle model
Solid: particles touching in a regular pattern, vibrating in place.
Liquid: particles touching but random, able to move past each other.
Gas: particles far apart, random, moving quickly in all directions.
Liquid: particles touching but random, able to move past each other.
Gas: particles far apart, random, moving quickly in all directions.
Changes of state
Melting (solid to liquid), boiling or evaporating (liquid to gas), condensing (gas to liquid), freezing (liquid to solid) and subliming (solid straight to gas).
These are physical changes: no new substances are made, and they can be reversed.
These are physical changes: no new substances are made, and they can be reversed.
Predicting the state
Compare the temperature with the melting point (mp) and boiling point (bp).
Below mp: solid. Between mp and bp: liquid. Above bp: gas.
Below mp: solid. Between mp and bp: liquid. Above bp: gas.
Bromine melts at −7 °C and boils at 59 °C. What state is it at 20 °C?
- 20 °C is above the melting point, so it is not solid.
- 20 °C is below the boiling point, so it is not a gas.
- It is a liquid.
Answer: Liquid
Solid: fixed pattern. Liquid: touching but moving. Gas: far apart and fast. Below mp solid, between mp and bp liquid, above bp gas.
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