Grade 7 ScienceGrade 7 ScienceUnit 3: Solutions & Unit 3: Solutions &

SubstancesSubstances

Observing MatterObserving Matter

MatterMatter is anything that has a mass is anything that has a mass and takes up space.and takes up space.

Imagine you could hold a rain drop in Imagine you could hold a rain drop in your hand, how you would describe your hand, how you would describe it? it?

Shape

Volume

Particle Arrangement

Particle Movement

The Particle Theory of The Particle Theory of MatterMatter

1.1. All matter is made up of tiny All matter is made up of tiny particlesparticles..2.2. These particles are always These particles are always movingmoving; they ; they

have have energyenergy..3.3. There are There are spacesspaces among the particles. among the particles.4.4. There are There are attractive forces attractive forces between between

the particles-these attractions may be the particles-these attractions may be strong or weak.strong or weak.

5.5. The particles of one substance differ The particles of one substance differ from the particles of other substances.from the particles of other substances.

Thermal Expansion Thermal Expansion (p.149-150)(p.149-150)

From the last unit, we learned that matter From the last unit, we learned that matter expands when heated. This can be expands when heated. This can be explained using the explained using the particle theory of particle theory of mattermatter..– When matter is heated, the particles When matter is heated, the particles gain gain

energyenergy..– Particles begin to Particles begin to move more move more and and spread spread

out.out.– This causes the matter to This causes the matter to increase its increase its

volume volume (get bigger).(get bigger).

Thermal Contraction Thermal Contraction (p.149-(p.149-150)150)

When substances are cooled, they When substances are cooled, they contract. Try to complete this yourself!contract. Try to complete this yourself!• When matter is ______, the particles ______ When matter is ______, the particles ______

energy.energy.• Particles have ______ movement and move Particles have ______ movement and move

_______ together._______ together.• This causes the matter to ______ its volume This causes the matter to ______ its volume

(get ______).(get ______).

• Complete the “Reading Check”, p. 150: #1-3Complete the “Reading Check”, p. 150: #1-3

States of MatterStates of Matter

As you are already aware, there are As you are already aware, there are three states of matter:three states of matter:– SolidSolid– LiquidLiquid– GasGas

These states can also be explained These states can also be explained using the using the particle theory of matterparticle theory of matter..

Three States of MatterThree States of Matter SolidSolid

– Definite shapeDefinite shape very little energyvery little energy particles only vibrate particles only vibrate particles are not free to move aroundparticles are not free to move around

– Definite volumeDefinite volume particles are held together by strong forces.particles are held together by strong forces.

Three States of MatterThree States of Matter LiquidLiquid

– Indefinite shapeIndefinite shape Particles move more freelyParticles move more freely Particles take the shape of their containerParticles take the shape of their container

– Definite volumeDefinite volume Particles are held together by strong Particles are held together by strong

attractions. attractions.

Three States of MatterThree States of Matter GasGas

– Indefinite ShapeIndefinite Shape Particles are moving constantly (a lot of Particles are moving constantly (a lot of

energy) and randomly in all directions.energy) and randomly in all directions. Takes the shape of the container and will fill Takes the shape of the container and will fill

the container.the container.

– Indefinite VolumeIndefinite Volume Attractions are very weak and particles are Attractions are very weak and particles are

far apart.far apart.

Changes of StateChanges of State Substances can change between these three Substances can change between these three

states. Do you recognize these changes of state?states. Do you recognize these changes of state?– MeltingMelting

Ice (solid) melts to water (liquid)Ice (solid) melts to water (liquid)

– EvaporationEvaporation Water (liquid) evaporates into steam (gas)Water (liquid) evaporates into steam (gas)

– CondensationCondensation Steam (gas) condenses to water (liquid)Steam (gas) condenses to water (liquid)

– FreezingFreezing Water (liquid) freezes to ice (solid)Water (liquid) freezes to ice (solid)

– SublimationSublimation Steam to ice OR ice to steam (skips the liquid phase)Steam to ice OR ice to steam (skips the liquid phase)

Changes of State (PTM)Changes of State (PTM) Here are the basics of the changes of state Here are the basics of the changes of state

according to the PTM:according to the PTM:– When the particles of a solid gain enough When the particles of a solid gain enough

energyenergy (from heat) to (from heat) to move freelymove freely, the , the substance becomes a liquid (substance becomes a liquid (loses its loses its shapeshape).).

– With even more energy, the particles may With even more energy, the particles may begin to begin to break free break free from the surface of the from the surface of the liquid (liquid (attractions become weakattractions become weak) and the ) and the substance becomes a gas.substance becomes a gas.

Can you guess what happens when the Can you guess what happens when the particles lose energy (cooled)?particles lose energy (cooled)?

Changes of StateMelting

Melting: changing from a solid to a liquid.– According to the particle theory of matter:

Temperature warms to above 0oC. 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 melting

Changes of StateEvaporation

Evaporation: liquid to a gas– According to the particle theory of

matter: Temperature warms to above 100oC. 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 StateCondensation

Condensation: gas to a liquid.– According to the particle theory of matter:

Temperature cools to below 100oC. 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 StateFreezing

Freezing: liquid to a solid– According to the particle theory of

matter: Temperature cools to below 0oC. 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 StateSublimation

Sublimation: solid to a gas.– According to the particle theory of

matter: Temperature warms from below 0oC to

above 100oC 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 StateSublimation (crystallization)

Sublimation: gas to a solid – According to the particle theory of matter:

Temperature…

Energy…

Movement…

– This means…

Attractions…

– This means…

States of MatterStates of Matter

Check out the following website:Check out the following website:– http://www.chem4kids.com/files/matter_

intro.html