CHEMISTRY · Stage 7 · Chapter 1: The Particle Model and States of Matter
Chemistry 1.3 Using the particle model — Explaining Compression, Flow and Shape
5 min read 8 parts Lesson 3 of 8
Lesson summary
1.3 Using the particle model — Explaining Compression, Flow and Shape — Alhussan International Academy — Chemistry (Stages 7–9) notes: Use the particle model to explain why solids, liquids and gases differ in shape, flow and compressibility, and define a vacuum.Basic idea — all m…
- Solids and liquids
- Aerosol cans
- Scuba and firefighters' cylinders
- Hydraulic jacks and brakes
- Bicycle pumps
- Change of state
Section 1 of 8The particle model of three states
- Basic idea
- all matter is made of tiny particles that are always in motion.
- The state depends on how the particles are arranged and how strongly they attract each other.
- Solid
- particles touch in a regular pattern, hold together strongly and vibrate about fixed positions.
- Liquid
- particles touch in a random arrangement and move past one another.
- Gas
- particles are far apart, move quickly in random directions and have very weak forces between them.
Section 2 of 8Explaining shape
1Solid2 points
- it keeps its own shape because its particles are held in fixed positions by strong forces.
- Solid carbon dioxide (dry ice) lumps keep their shape and size if kept cold.
2Liquid2 points
- it has a fixed volume but takes the shape of its container, because particles slide over each other but stay in contact.
- The shape of liquid water keeps changing when a child pours it from jar to jar.
3Gas2 points
- it spreads out to fill any container, because particles move freely and the forces between them are too weak to hold them in one place.
- Carbon dioxide gas spreads out and mixes with the air all around the Earth.
Section 3 of 8Explaining flow
1Fluids2 points
- liquids and gases are called fluids because their particles move from place to place, so they can flow.
- Liquid mercury flows and carbon dioxide flows in the gas state.
2Solids2 points
- a solid cannot flow because its particles are in fixed positions and cannot change places.
- Solid mercury and solid carbon dioxide cannot flow.
3Powders2 points
- sand seems to pour, but each grain is a tiny solid.
- The grains slide over one another and the particles inside each grain are still locked in place.
Section 4 of 8Explaining compression
- Compress = to squeeze a substance into a smaller volume, which is only possible if there is empty space between particles.
- Gases
- all substances can be compressed in the gas state, because the particles are far apart and get closer together when squeezed.
- The particles themselves stay the same and do not change size.
- The oxygen in a firefighter's cylinder would normally fill about 1000 soda bottles.
- Solids and liquids
- they can be compressed only a very tiny bit, because their particles are already touching.
Section 5 of 8Comparing the states
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Fixed | Takes container shape | Fills container |
| Can flow | No | Yes | Yes |
| Compressible | No | Almost not | Yes |
| Density | High | High | Low |
Section 6 of 8Vacuum
- Vacuum = a space that has no particles and so no matter.
- Most of outer space is close to a vacuum, though a few particles are very far apart.
Section 7 of 8Everyday applications
- Dry ice
- solid carbon dioxide packed around vaccine bottles keeps them very cold.
- Aerosol cans
- they hold gas squeezed into a small volume, and the particles spread out when the valve opens.
- Scuba and firefighters' cylinders
- many gas particles are packed into a small container.
- Hydraulic jacks and brakes
- liquid cannot be compressed, so a force applied at one point is passed on through the liquid to another point.
- Bicycle pumps
- they use air, which is easily compressed.
Section 8 of 8Giving a full explanation
- State the property, describe the particle arrangement and movement, then link the two.
- Change of state
- the particles themselves stay the same, and only the arrangement, spacing and energy change, so the mass is unchanged.
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