Grade 9 Chemistry - Lesson 1

Matter and the Particle Theory

What is Matter?

• Matter is anything that contains both mass and volume.

Mass

• Mass is the amount of matter in an object.
• Measured in grams, kilograms, milligrams, etc.
• Different from weight: mass remains constant regardless of location (e.g., Earth, space) while weight varies with gravitational pull.

Volume

• Volume is the amount of space something occupies.
• Measured in liters, milliliters, etc.

States of Matter

• Solid: e.g., rock
• Liquid: e.g., water
• Gas: e.g., air in a balloon

Changes of State

• Melting: Solid to liquid (e.g., ice melting), melting point = freezing point (0°C for water).
• Freezing: Liquid to solid (e.g., water freezing).
• Evaporation: Liquid to gas (e.g., boiling water).
• Condensation: Gas to liquid (e.g., condensation on a cold pop can).
• Sublimation: Solid to gas (e.g., dry ice).
• Deposition: Gas to solid (e.g., frost).

Particle Theory

• 1. All matter is made up of tiny particles.
• 2. Particles have spaces between them.
• 3. Particles of a pure substance are identical; different substances have different particles.
• 4. Particles are always in motion; more energy = faster movement.
• 5. Attractive forces between particles; stronger when particles are closer.

Particle Theory & States of Matter

• Adding energy to particles increases their movement and weakens bonds.
  • Solid: Low energy, particles vibrate in place.
  • Liquid: More energy, particles slide past each other.
  • Gas: High energy, particles move independently.

Why Do Puddles Evaporate?

• Evaporation occurs below boiling point because some particles have enough energy to become a gas even at lower temperatures.

Next Lesson

• Mixtures and Pure Substances