Unit 2
Materials and
Their structure
Year 7
2.1 Solids, Liquids
and Gases
Key Words 1
● Compressed: To be pushed or squeezed into a smaller space, often
increasing its density.(Solids cannot be compressed)
● Flow: The continuous movement of a liquid, gas, or other fluid substance,
typically from one place to another.
● Hypothesis: A testable theory
● Matter: Anything that has mass and takes up space (has volume),
composed of tiny particles.
● Particle: A tiny piece of matter, that is in constant motion and makes up all
substances.
Key Words 2
● Pour: To cause a liquid or a gas made of many small particles to move
smoothly
● Property: The characteristics and behavior of a material.
● States of Matter: The forms in which matter exists (solid, liquid, gas).
● Theory: An idea used to explain evidence.
● Vacuum: An empty area without particles.
● Vibrate: To move back and forth repeatedly.
● Volume: The amount of space occupied by matter.
.
States of
Matter
• Matter: Everything we can see and feel.
• 3 States: Solids, Liquids, Gases.
• Properties = how they behave.
.
States of
Matter
Solids Liquids Gases
1. Keep the same shape 1. Take the shape of their 1. Fill the whole container.
and volume. container. - 2. Can be compressed.
2. Cannot be compressed 2. Can be poured but not 3. Volume can change.
or poured. compressed. 4. Hard to see, but can
3. Has fixed volume 3. Volume stays the same. smell or feel them (e.g.,
air).
“
How Matter Behaves
- Scientists explain matter using observations, hypotheses, and
theories.
- Examples of behavior:
Smell food cooking in another room.
Substances expand when heated.
Liquids → solids when cooled.
- Theory of Particles:
All matter is made of tiny particles too small to see.
Particles are arranged differently in solids, liquids, and gases.
Particle Theory
Solids
- Particles packed tightly in fixed positions.
- Strong forces hold them → fixed shape.
- Can only vibrate.
Liquids
- Particles touch but are not tightly packed.
- Weaker forces → particles move and slide past each
other.
Liquids change shape but keep volume.
Gases
- Particles are far apart, no fixed arrangement.
- Move freely and spread out.
- Easy to compress, change shape and volume.
Explaining Properties of Matter
- Matter can flow (be poured) if particles move past
each other.
- Matter can change volume if particles spread out or
move closer together.
Solids Liquids Gases
Particles are tightly packed, Particles close together but can Particles far apart, weak/no
held by strong forces. slide past each other. forces.
Fixed shape, cannot flow. Fixed volume but no fixed shape. No fixed shape or volume.
Only vibrate in place. Can flow but cannot be Move freely, spread out,
compressed. easy to compress.
2.2 Changes of
State
Key Words 1
● Melt: change from a solid to a liquid
● Melting point: the temperature at which a solid changes to a liquid
● Water vapor: a gas formed by water droplets in the air, at air temperature
● Evaporation: changing from a liquid to a gas, at a temperature below
boiling point
● Boil: heating strongly and changing a liquid to a gas
● Boiling point: the temperature at which a liquid changes to a gas
● Thermometer: a device that measures temperature
Key Words 2
● steam: water vapor produced when water boils and changes from a
liquid to a gas
● condensation (condenses): changing from a gas to a liquid, for
example water vapor changing to liquid water
● freeze: changing from a liquid to a solid
● changes of state; when one state of matter changes to become
another state of matter
● measuring cylinder: a piece of glassware designed for measuring the
volume of liquids
● meniscus: the slight curve at the surface of a liquid, more clearly seen
when the liquid is in a narrow container
Changing State
•Melting: Solid → Liquid (melting point)
•Evaporation: Liquid → Water vapor (invisible gas)
•Boiling: Liquid → Steam at 100 °C (boiling point)
•Condensation: Gas → Liquid (when cooled)
•Freezing: Liquid → Solid (freezer → ice)
•These are called changes of state.
Measuring Volume
•Use a measuring cylinder.
•The liquid forms a meniscus (curved surface).
•Read at the bottom of the meniscus.
•Keep your eye level with the liquid.
Measuring Temperature
•Use a thermometer.
•Liquid inside expands when heated → rises.
•Read the temperature at the top of the liquid.
•Keep your eye level with the scale.
2.3 Explaining
Changes of Matter
Changing State
- Matter can change state when heated or cooled.
- Heat energy changes how particles move.
- Stronger heating → more vibration/movement.
- Cooling → particles slow down and get closer together.
Changing State
- Heating Solids
Solids expand when heated.
Particles:
Arranged in fixed pattern.
Vibrate more when heated.
Heat energy transferred → particles move faster.
Still held by attractive forces.
- Melting Solids
More heating → solids melt into liquids.
Particles vibrate so much they escape strong forces.
Particles slide past each other → liquid form.
Changing State
- Boiling Liquids
When heated, liquids boil/evaporate.
Particles move faster, spread apart.
Weak forces broken → particles escape as gas.
- Cooling Gases
Gas particles move freely, no forces holding them.
Cooling → energy lost.
Particles move closer → form liquid (condensation).
Example: gas on a cold surface forms liquid drops.
- Freezing Liquids
Cooling a liquid → freezes to solid.
Particles slow down, less movement.
Eventually, cannot flow → arranged in fixed pattern.
Form a solid again.
2.4 The Water Cycle
Key Words 1
- Atmosphere: The mixture of gases around earth
- Groundwater: Water from precipitation that has soaked into the soil and rocks
on the ground.
- Open water: Larg lakes and oceans
- Precipitation: The process of water in the atmosphere falling to earth. This can
result in a fall of rain, snow, hail or sleet.
- Surface run-off: Rainwater that reaches the surface of the land and flows into
rivers, lakes and oceans.
Key Words 2
- Transpiration: A loss of plants vapour from plants leaves.
- Water cycle: The processes by which water on Earth is recycled around the
environment from rivers and oceans to clouds and back again.
- Water vapour: A gas formed by the little droplets of water that exist in the air
at the temperature of the air.
The Water Cycle
Water is vital for all living things.
Our bodies are about 60% water.
Water on Earth is constantly moving.
The water cycle: continuous recycling of water between atmosphere, land, rivers, lakes,
and oceans.
The same water has been recycled for over 4 billion years.
The Water Cycle
1. Water Moves into the Atmosphere
Heat from the Sun warms water in rivers, lakes, and oceans.
Some water changes into water vapour (evaporation).
Plants also release water vapour into the air (transpiration).
2. Cooling in the Atmosphere (Condensation)
As water vapour rises, it cools.
Cooled vapour condenses into tiny droplets → clouds.
This process is called condensation.
3. Water Falls from Clouds (precipitation)
When droplets in clouds become too heavy → fall to Earth.
This is precipitation: rain, snow, hail, or sleet.
The Water Cycle
Open water: rivers, lakes, seas, and oceans.
Collects most of the precipitation that falls.
Provides water for:
Drinking and daily use.
Plants and animals.
Evaporation back into the atmosphere.
Surface run-off: Some precipitation flows over the land surface into rivers and lakes.
Ground Water: Water soaks into soil and rocks → groundwater.
The Water Cycle
Key Processes
Evaporation – liquid water → vapour.
Transpiration – water released from plants.
Condensation – vapour → liquid droplets (clouds).
Precipitation – rain, snow, hail, sleet.
Collection – water stored in rivers, lakes, oceans, or ground.
