Chemistry GCSE Revision

ATOMIC STRUCTURE

Topic 1

What is an atom?

The smallest unit of matter. The basic building block of matter.

What is a compound?

Compounds are substances formed when 2 or more different elements are CHEMICALLY bonded together in a fixed ratio.

Name the 4 key features of a chemical reaction.

• Compounds are broken up or formed

• At least 1 new substance is created

• Measurable energy change

• No atoms are created or destroyed

What is a chemical equation and what does it show?

A chemical equation shows what happens in a chemical reaction using symbols or words.

Reactants - Products

What are mixtures?

Mixtures are made of 2 or more substances (elements or compounds) that have NOT been chemically combined. Mixtures can be separated. An example is air, it is a mixture of different gases.

Name the 5 separation techniques

Filtration, Crystallisation, Filtration, Simple Distillation, Fractional Distillation.

Describe the process of Filtration.

• Filtration separates mixtures that contain insoluble (can’t dissolve) solids and liquids (they ARE soluble).

Filtration is performed by pouring the mixture through filter paper:

• The insoluble solid is trapped by the filter paper

• The liquid runs through the filter paper and is collected below

Describe the process of Crystallisation

• Crystallisation separates solutions into their different parts: dissolved solids (solutes) and liquids (solvents)

Crystallisation is performed by heating the mixture so that the solvent evaporates

• Eventually, crystals of the solute (dissolved solids) will form

• We can collect the solvent (liquid) by condensing as it evaporates.

Describe the process of Chromatography.

• Chromatography separates solutions with a number of different solutes (solids) in the solvent (liquids)

• Place a drop of the solution to be separated near the bottom of a piece of chromatography paper. Dip the very bottom of the paper into a suitable solvent. The solvent (liquid) moves up the paper and carries the solutes (solids) in the solution with it

• Different solutes (solids) move at different speeds, so they separate on the paper

What is Distillation?

Distillation is a special technique used to separate mixtures of liquids. It uses the different boiling points of liquids to separate them. There are 2 types: Simple and Fractional

Describe the process of Simple Distillation.

Separates 2 liquids with different boiling points

• The mixture is heated until the liquid with the lower boiling point starts to boil

• The vapour released passes through a condenser, where the gas boils back into a liquid

Simple distillation can ALSO separate a solute from a solvent, when the solvent has a lower boiling point than the solute