Scientific ideas, concepts and processes
Physical properties of solids, liquids and gases: What can we measure about solids, liquids and gases?
Solids are incompressible, have a fixed shape and a higher density.
Liquids are incompressible, have no fixed shape, can be poured and have a fairly high density.
Gases are compressible, have no fixed shape, can be poured and have a low density.
Liquids and gases can diffuse.
Particle theory: Is everything made of moving particles?
Particles that make up a pure substance can be atoms or molecules.
Particles in a solid are strongly held together and vibrate about fixed positions.
As a solid is heated, the particles vibrate faster.
At absolute zero (-273°C) the particles stop moving.
Particles in a liquid are more weakly held together and move around.
Particles in a gas move around quickly and randomly, colliding and bouncing off each other and the walls of the container.
When a liquid or gas is heated, the particles move faster.
Particles are very small, and are not destroyed or made during physical changes, such as melting, boiling, solidifying, condensing or dissolving.
The overall mass of particles stays the same when a physical change happens.
Particle theory can be used to explain thermal expansion, diffusion, stretching and heat transfer.
Changes of State: Can any substance exist as a solid, liquid or gas?
A higher temperature means faster particles with more energy.
At absolute zero (-273°C), the particles stop moving completely.
A change of state takes in or gives out energy.
A solid changes to a liquid (and a liquid to a solid) at the melting point.
A liquid changes to a gas (and a gas to a liquid) at the boiling point.
The boiling point of water is 100°C and the melting point of ice is 0°C, at standard pressure.
Sublimation occurs in a few substances when they change directly between a solid and a gas.
Solutions: Where does the solid go when it dissolves in a liquid?
A solute dissolved in a solvent makes a solution.
Gases can also dissolve in liquids.
When a solid dissolves in a liquid, the particles are too small to see, but are still there, so mass is conserved (the total stays the same).
Substances can be classified as soluble or insoluble.
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