C1.1 Particles · KS3 Science

The particle model

All matter is made of tiny particles.
How the particles are arranged and how they move decides whether something is a solid, liquid or gas.

Particles are close together but in a random arrangement.
They can slide past each other, so liquids flow and take the shape of their container.
Liquids have a fixed volume and are very hard to squash.

Particles are far apart and move quickly in all directions.
Gases have no fixed shape or volume. They spread out to fill any container and can be squashed.
Gas pressure is caused by particles colliding with the walls of their container.

Melting (solid → liquid), freezing (liquid → solid), evaporating or boiling (liquid → gas), condensing (gas → liquid), sublimation (solid → gas).
Heating gives particles more energy, so they move faster.
The mass stays the same when a substance changes state.
Diffusion (particles spreading out) is faster in gases than in liquids, and faster when it is warmer.

Density = mass ÷ volume. It is measured in g/cm³ (or kg/m³).
Example: a block with a mass of 60 g and a volume of 20 cm³ has a density of 60 ÷ 20 = 3 g/cm³.
Solids are usually denser than liquids because their particles are packed more closely. Gases have very low densities.
Objects less dense than water (1 g/cm³) float. Ice floats because it is slightly less dense than liquid water.
To find the volume of an irregular object, lower it into water and measure how much the water level rises (displacement).

The independent variable is what you change. The dependent variable is what you measure. Control variables are kept the same to make it a fair test.
Repeat readings and calculate a mean to make results more reliable.

Particle: A tiny piece of matter, such as an atom or molecule.
Melting: A solid turning into a liquid.
Freezing: A liquid turning into a solid.
Evaporation: A liquid turning into a gas at its surface, below its boiling point.
Condensation: A gas turning into a liquid.
Sublimation: A solid turning straight into a gas.
Diffusion: Particles spreading from where there are lots of them to where there are fewer.
Gas pressure: The force from gas particles colliding with the walls of a container.
Density: How much mass there is in a certain volume (mass divided by volume).
Independent variable: The variable you change in an investigation.
Dependent variable: The variable you measure in an investigation.
Control variable: A variable kept the same to make a fair test.