Particle Model of Matter
Solids, liquids, gases and changes of state
The Particle Model of Matter
All matter is made up of tiny particles. In solids, particles are tightly packed and vibrate in fixed positions. In liquids, particles are close but can slide past each other. In gases, particles are far apart and move freely.
Example
Changes of State
Melting: solid to liquid (ice at 0 degrees C). Boiling: liquid to gas (water at 100 degrees C). Condensation: gas to liquid (steam on a cold window). Freezing: liquid to solid. During changes of state, energy is added or removed.
Note
Key Point
The particle model explains why solids have a fixed shape, liquids take the shape of their container, and gases fill any space. Heating makes particles move faster.
Key Vocabulary
ParticleA very small piece of matter, such as an atom or molecule
State of matterThe form matter takes: solid, liquid, or gas
EvaporationWhen a liquid changes to a gas at its surface
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