21. States of Matter & Changing State
1. The Three States of Matter
State | Arrangement & Forces | Movement & Shape |
Solid | Strong forces of attraction hold particles close together in a fixed, regular lattice structure. | Particles vibrate in fixed positions. They keep a definite shape and volume; they cannot flow. |
Liquid | Weak forces of attraction. Particles are randomly arranged but tend to stay close and compact. | Particles are free to move around each other. They have a definite volume but no fixed shape (they flow to fit a container). |
Gas | Very weak forces of attraction between particles. Particles are far apart. | Particles move quickly and in straight lines in any direction. They have no definite shape or volume and fill their container. |
2. Changing State
Changes of state occur when energy is added or removed, affecting the forces between particles:
Melting (Solid to Liquid): Heating a solid gives particles energy to vibrate more. At the melting point, they gain enough energy to break free from their fixed positions.
Boiling/Evaporating (Liquid to Gas): Heating a liquid makes particles move faster. At the boiling point, they gain enough energy to break the bonds holding them together entirely.
Condensing (Gas to Liquid): Cooling a gas reduces particle energy. They move slower, and forces of attraction begin to pull them together into a liquid.
Freezing (Liquid to Solid): Cooling a liquid further reduces energy until the particles move so slowly that more bonds form, fixing them in a solid lattice.
3. Limitations of Particle Theory
While useful, the simple "sphere" model of particles has limitations:
In reality, particles are not solid, inelastic spheres; they are complex atoms, ions, or molecules.
The model does not detail the specific strength or number of forces between particles.