Chemistry revision notes

Everything is made of atoms. Knowing the particles inside an atom and how they are arranged underpins the whole of chemistry.

Bonding explains why substances have the properties they do. The three types — ionic, covalent and metallic — each come from how electrons are shared or transferred.

Quantitative chemistry lets you predict exactly how much product a reaction gives. It rests on the mole, Mr and the conservation of mass.

Chemical changes rearrange atoms into new substances. This topic covers acids, the reactivity series, salt preparation and electrolysis.

Chemical reactions transfer energy to or from the surroundings. Bond breaking is endothermic; bond making is exothermic — the difference is the overall energy change.

Rate of reaction is how fast reactants are used up or products are formed. Collision theory explains every factor that changes it.

Organic chemistry is the chemistry of carbon compounds. At GCSE the focus is crude oil, hydrocarbons and simple reactions of alkanes and alkenes.

Analysis lets chemists identify substances and check purity. Techniques range from chromatography and Rf values to simple gas and ion tests.

Today's atmosphere is roughly 78% nitrogen and 21% oxygen. Human activity is now changing its composition, causing climate change.

Chemistry provides the materials we depend on. Sustainable use means treating water carefully, assessing product life cycles and recycling metals and polymers.

Chemistry starts with the atom. This unit sets out the particles inside atoms, the difference between elements, compounds and mixtures, and how to describe them for IGCSE.

The kinetic particle model explains why solids, liquids and gases behave differently — and lets you predict what happens when we heat, cool or mix substances.

The properties of any substance come from the bonding between its particles. IGCSE focuses on three types of bonding and the structures they form.

Stoichiometry is the arithmetic of chemistry — using balanced equations and moles to work out how much of each substance reacts or is made.

The periodic table organises elements by proton number. Elements in the same group have similar properties because they have the same number of outer electrons.

Acids donate H⁺ ions; bases accept them. Combining them neutralises to give a salt and water. Salt preparation is a classic IGCSE practical.

How a metal is extracted depends on its position in the reactivity series. Reactive metals need electrolysis; less reactive metals are reduced by carbon.

Rates of reaction are all about how often particles collide with enough energy. Reversible reactions can reach a dynamic equilibrium where forward and backward rates are equal.

Organic chemistry is the chemistry of carbon compounds. Most start life in crude oil and are used as fuels, plastics and chemicals.

This unit connects chemistry to everyday life — the air we breathe, the water we drink, the fuels we burn and the impact on our environment.