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Chemists use symbols and formulae to represent elements and compounds. Word equations and balanced chemical equations represent the changes that happen in chemical reactions.

There are different ways to separate mixtures, such as filtration, crystallisation, simple distillation, fractional distillation and chromatography. The method chosen depends on the type of mixture.

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in shells. The number of subatomic particles in an atom can be calculated from the atom's atomic number and mass number.

Mendeleev made an early periodic table. In the modern periodic table, elements are in order of atomic number in periods and groups. Electronic structures model how electrons are arranged in atoms.

Elements in the same group of the periodic table show trends in physical properties, such as boiling point. They have the same number of electrons in their outer shell, so they are similar in their chemical properties.

The transition elements are metals. They have high melting points and densities, and are strong and hard. They form coloured compounds and act as catalysts.

Understanding how to approach exam questions helps to boost exam performance. Question types will include multiple choice, structured, mathematical and practical questions.