The particle model | Year 7 Chemistry (Cambridge) - Class 7 PDF Download

Introduction

• Matter exists in three main states: solid, liquid, and gas.
• These states can change based on temperature and pressure.

Solids

• Description:
  • Particles are tightly packed in a fixed, regular arrangement.
  • Particles vibrate but do not move from their positions.
  • Strong forces exist between particles.
• Example:
  • Ice (solid water) maintains its shape and volume.

Liquids

• Description:
  • Particles are close together but can move past each other.
  • Particles have an irregular arrangement.
  • Weak forces exist between particles.
• Example:
  • Water flows and takes the shape of its container.

Gases

• Description:
  • Particles are far apart and move freely.
  • Particles have a random arrangement.
  • Very weak forces exist between particles.
• Example:
  • Steam (water vapor) spreads to fill any container.

Changes of State

• Melting: Solid to liquid by heating (e.g., ice melting into water).
• Freezing: Liquid to solid by cooling (e.g., water freezing into ice).
• Boiling (Vaporization): Liquid to gas by heating (e.g., water boiling into steam).
• Condensation: Gas to liquid by cooling (e.g., steam condensing into water).
• Sublimation: Solid to gas without passing through liquid state (e.g., dry ice sublimating into carbon dioxide gas).

Demonstration

Visual Example:

• Show how solids retain shape, while liquids and gases take the shape of their containers.
• Demonstrate using ice cubes, water, and steam to illustrate each state.

Conclusion

• Understanding states of matter helps explain how substances behave under different conditions.
• Temperature changes play a crucial role in altering states of matter.