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Pure Substances�and Mixtures

Grade 7 Science

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Matter

Lesson 1

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Matter

  • Matter is all around us - it is anything that takes up space and has mass.
  • All matter is made of tiny particles.
  • The particle theory of matter explains how matter behaves.

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The Particle Theory of Matter States…

    • All matter is made of tiny particles. Each substance has its own unique particles.

Substance A

Substance B

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The Particle Theory of Matter States…

    • There are empty spaces between the particles that are very large compared to the particles themselves.

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The Particle Theory of Matter States…

    • Particles are held together by very strong electric forces.

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The Particle Theory of Matter States…

    • Particles are always in motion. When they are heated, they move faster and spread farther apart.

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Matter

  • Matter exists in three states: solid, liquid, and gas.
    • Remember: each substance has unique particles.
    • Particles of a substance do not change when the substance changes state – it is their movement that changes.

SOLID

LIQUID

GAS

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Solids

  • Solids have a definite volume and shape.
  • The particles in a solid substance are packed very closely together.
  • The particles in a solid vibrate slightly, but stay in the same place.

DEFINITE means UNCHANGING

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Liquids

  • Liquids have a definite volume but do not have a definite shape (their shape changes to the shape of their container).
  • Particles in a liquid are also close together, but they are free to move around each other.
  • Particles in a liquid vibrate more rapidly than those in a solid.

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Gasses

  • Gasses do not have definite volumes or shapes. They take the shape of and fill their container.
  • Particles in a gas are spread far apart and move very quickly.
  • Particles in a gas vibrate more rapidly than those in solids or in liquids.

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Summary

State of Matter

Shape

Volume

Solid

Definite

Definite

Liquid

Indefinite

Definite

Gas

Indefinite

Indefinite

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Change of State

  • A change of state can occur if energy (heat)�is added or removed.
    • Particles move faster when energy is added.
    • Particles move slower when energy is removed.

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Change of State

  • Example: Ice becomes steam.
    • When water is a solid, the particles are packed very tightly.
    • When heat is added, the particles start to move faster and spread farther apart, becoming a liquid (melting).
    • If we continue adding heat, the particles will vibrate even faster and move far enough apart that�they will become a gas (evaporation).

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Change of State

  • Example: Steam becomes ice.
    • The particles in steam are moving very quickly and are very far apart.
    • As heat is removed, the particles move slower and slower until they form a liquid (condensation).
    • If we remove enough heat, the particles move even slower and stay closer together,�becoming a solid (freezing).