Grade 7 Science Unit 3: Solutions & Substances

Observing Matter Matter is anything that has a mass and takes up space. Matter is anything that has a mass and takes up space. Imagine you could hold a rain drop in your hand, how you would describe it? Imagine you could hold a rain drop in your hand, how you would describe it?  Shape  Volume  Particle Arrangement  Particle Movement

The Particle Theory of Matter 1. All matter is made up of tiny particles. 2. These particles are always moving; they have energy. 3. There are spaces among the particles. 4. There are attractive forces between the particles-these attractions may be strong or weak. 5. The particles of one substance differ from the particles of other substances.

Thermal Expansion (p ) From the last unit, we learned that matter expands when heated. This can be explained using the particle theory of matter. From the last unit, we learned that matter expands when heated. This can be explained using the particle theory of matter. –When matter is heated, the particles gain energy. –Particles begin to move more and spread out. –This causes the matter to increase its volume (get bigger).

Thermal Contraction (p ) When substances are cooled, they contract. Try to complete this yourself! When substances are cooled, they contract. Try to complete this yourself! When matter is ______, the particles ______ energy. When matter is ______, the particles ______ energy. Particles have ______ movement and move _______ together. Particles have ______ movement and move _______ together. This causes the matter to ______ its volume (get ______). This causes the matter to ______ its volume (get ______). Complete the “Reading Check”, p. 150: #1-3 Complete the “Reading Check”, p. 150: #1-3

States of Matter As you are already aware, there are three states of matter: As you are already aware, there are three states of matter: –Solid –Liquid –Gas These states can also be explained using the particle theory of matter. These states can also be explained using the particle theory of matter.

Three States of Matter Solid Solid –Definite shape  very little energy  particles only vibrate  particles are not free to move around –Definite volume  particles are held together by strong forces.

Three States of Matter Liquid Liquid –Indefinite shape  Particles move more freely  Particles take the shape of their container –Definite volume  Particles are held together by strong attractions.

Three States of Matter Gas Gas –Indefinite Shape  Particles are moving constantly (a lot of energy) and randomly in all directions.  Takes the shape of the container and will fill the container. –Indefinite Volume  Attractions are very weak and particles are far apart.

Changes of State Substances can change between these three states. Do you recognize these changes of state? Substances can change between these three states. Do you recognize these changes of state? –Melting  Ice (solid) melts to water (liquid) –Evaporation  Water (liquid) evaporates into steam (gas) –Condensation  Steam (gas) condenses to water (liquid) –Freezing  Water (liquid) freezes to ice (solid) –Sublimation  Steam to ice OR ice to steam (skips the liquid phase)

Changes of State (PTM) Here are the basics of the changes of state according to the PTM: Here are the basics of the changes of state according to the PTM: –When the particles of a solid gain enough energy (from heat) to move freely, the substance becomes a liquid (loses its shape). –With even more energy, the particles may begin to break free from the surface of the liquid (attractions become weak) and the substance becomes a gas. Can you guess what happens when the particles lose energy (cooled)? Can you guess what happens when the particles lose energy (cooled)?

Changes of State Melting Melting: changing from a solid to a liquid. – –According to the particle theory of matter:   Temperature warms to above 0 o C.   Particles gain energy and hence have more movement. – –Loses its shape (particles are free to move)   Attractions, however, are still strong. – –Keeps its volume   Substance is now a liquid since it has indefinite shape but definite volume. – –Animation of ice meltingAnimation of ice melting

Changes of State Evaporation Evaporation: liquid to a gas – –According to the particle theory of matter:   Temperature warms to above 100 o C.   Particles gain a lot of energy and move randomly in all directions. – –Still has no shape   Attractions become weak and the particles break free from the surface of the liquid. – –Loses its volume   Substance is now a gas since it has indefinite shape and indefinite volume.

Changes of State Condensation Condensation: gas to a liquid. – –According to the particle theory of matter:   Temperature cools to below 100 o C.   Gas particles lose energy and do not have as much movement, but are still free to move around. – –Still has no shape   Particles again become attracted to each other. – –Regains its volume   Substance is now a liquid since it has indefinite shape but definite volume. – –Which process is the opposite of condensation?

Changes of State Freezing Freezing: liquid to a solid – –According to the particle theory of matter:   Temperature cools to below 0 o C.   Particles lose energy and have very little movement. – –Regains its shape   The attractions are still strong. – –Retains its volume   Substance is now a solid since it has a definite shape and definite volume.

Changes of State Sublimation Sublimation: solid to a gas. – –According to the particle theory of matter:   Temperature warms from below 0 o C to above 100 o C very quickly.   Particles gain a lot of energy and move randomly in all directions. – –Loses its shape   Attractions become very weak. – –Loses its volume   Substance is now a gas because…

Changes of State Sublimation (crystallization) Sublimation: gas to a solid – –According to the particle theory of matter:   Temperature…   Energy…   Movement… – –This means…   Attractions… – –This means…

States of Matter Check out the following website: Check out the following website: –