iGCSE Chemistry (Triple) Edexcel

Particles and Mixtures: States of Matter

• All matter is comprised of particles, these particles may be atoms, molecules or ions.
• The state of matter (solid, liquid or gas) is determined by how these particles are arranged and how they interact with one another.
• In a solid, the particles are packed closely together in a regular pattern. The particles vibrate but do not move from their fixed positions. This gives solids a definite shape and volume.
• Liquids have particles that are packed less tightly than in solids. They can move freely and slide past each other, giving liquids the ability to flow and take the shape of their container but having a fixed volume.
• Gaseous particles are widely separated with a lot of empty space between particles. They move rapidly and randomly. Gases do not have a definite shape or volume and they will always fill their container.
• Matter can change between these states by heating or cooling which gives/takes energy to/from the particles. Heating generally increases the speed of the particles and their energy, while cooling reduces their speed and energy.
• The change from a solid to a liquid state is called melting. The reverse process, the change of a liquid to a solid state, is called freezing or solidification.
• The change from a liquid to a gas state is called boiling or evaporation. The reverse process, the change of a gas to a liquid state, is called condensation.
• The change from a solid state directly to a gas state is called sublimation.
• In a mixture, two or more substances are combined but they do not combine chemically. Each substance in the mixture retains its own physical and chemical properties.
• Mixtures can contain elements, compounds or both, they can be separated by physical processes (e.g. filtration, evaporation, distillation). Therefore, mixtures are different from compounds which require a chemical reaction to separate.
• Solutions are types of mixtures. They consist of a solute (substance which is dissolved) and a solvent (substance in which the solute is dissolved). This can happen with gases, liquids and solids.
• The concentration of a solution refers to the amount of solute dissolved in a fixed amount of the solution. Dissolving more solute creates a more concentrated solution.
• Solubility refers to the maximum amount of solute that can be dissolved in a certain amount of solvent at a given temperature.
• Increasing the temperature generally increases the solubility of a solid in a liquid, but decreases the solubility of a gas in a liquid.