Pearson Science Double Award Chemistry 1: Principles of Chemistry

Chemical principles connect particle models to separation, atomic structure, equations, quantities and bonding. The 4SD0 Double Award boundary matters here: metallic bonding, ionic equations, solution concentration and electrolysis points found in separate Chemistry are not part of this topic.

Particles, states and solutions

In a solid, particles occupy fixed positions and vibrate. In a liquid they remain close but move past one another. In a gas they are widely separated and move rapidly in random directions. Heating increases particle energy, causing melting or boiling; cooling causes condensation or freezing. During a change of state, the substance remains chemically the same.

Diffusion is the net spreading of particles from higher to lower concentration. Gas diffusion is usually faster than liquid diffusion because gas particles move more rapidly and are farther apart.

A solute dissolves in a solvent to form a solution. A saturated solution contains the maximum dissolved solute possible at that temperature. Dilution lowers concentration by adding solvent; it does not destroy solute particles.

Pure substances and separation

An element contains one type of atom. A compound contains elements chemically combined in fixed proportions. A mixture contains substances not chemically bonded together. Pure substances have fixed melting and boiling points, while mixtures may change state across a range.

Choose separation by physical property:

• filtration separates an insoluble solid from a liquid;
• crystallisation recovers a soluble solid from solution;
• simple distillation recovers a solvent or separates liquids with widely different boiling points;
• fractional distillation separates miscible liquids with closer boiling points;
• paper chromatography separates soluble components by different attractions to the stationary and mobile phases.

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