• Particles exist in all matter; everything around you is made up of them!
• The three core states of matter are solids, liquids and gases, each possessing unique characteristics.
• In a solid, particles are tightly packed in a fixed structure, they vibrate but can't move from their position, hence explaining the solid's definite shape and volume.
• For liquids, particles are not as tightly packed as solids; they're not held in a fixed structure and possess the freedom to move around one another. The liquid's volume is definite, but shape isn't; it conforms to the shape of the container in which it is placed.
• The particles in a gas are much more spread out and move freely at high speeds in all directions. This explains why gases neither have a definite shape nor volume.
• Changing the state of matter involves energy. When energy is added (for example, by heating), particles move more and cause the matter to change states- solid to liquid (melting), liquid to gas (evaporation).
• If energy is lost (for example, by cooling), particles slow down, and the matter changes from gas to liquid (condensation) or liquid to solid (freezing).
• The temperature at which matter changes from one state to another (melting point, boiling point, etc.) is specific to each substance and is consistent under the same conditions.
• Brownian motion is a random motion observed in particles. It’s the erratic, random, zig-zag movement of microscopic particles in a fluid, as a result collisions with fast atoms or molecules in a gas or liquid.

Remember, practise using and interpreting particle models for solid, liquid and gas, as it can come up in your examinations. Differences in density, compressibility and motion should be familiarised and you should be able to explain how changes in energy can cause state changes.