Chemistry

Everything around you — solids, liquids and gases — is made of tiny particles you cannot see. This chapter explains the three states of matter in terms of how those particles are arranged, h

Most substances in everyday life — air, food, drinks — are mixtures . This chapter distinguishes elements (one type of atom), compounds (elements chemically combined in fixed proportions) an

The 118 elements are the building blocks from which everything is made — from simple substances such as carbon to complex ones such as DNA. This chapter explores the nature of atoms and mole

The Periodic Table arranges all elements by atomic number , into groups (columns) and periods (rows). Elements in the same group have the same number of outer electrons and therefore similar

This chapter is about the language and maths of chemistry : writing formulae and equations , balancing them, and calculating relative atomic/formula mass , percentage composition , moles , a

⚠️ This entire chapter is flagged ✩ CHEMISTRY ONLY (it sits between a "CHEMISTRY ONLY" header and an "END OF CHEMISTRY ONLY" marker) — extended-tier content. This chapter extends the mole id

A compound forms when two or more elements chemically combine. This chapter covers one way elements combine: transfer of electrons to form ionic compounds. Sodium (a dangerously reactive met

There are a lot more covalent compounds than ionic compounds, so it is important to understand how this bonding works. In a covalent bond, atoms are held together by sharing a pair of electr

Metals are built from a regular lattice of positive ions surrounded by a free-moving 'sea' of delocalised electrons. The electrostatic attraction between these two holds the metal together,

Passing electricity through an ionic compound that is molten or in solution causes a chemical change called electrolysis: positive ions (cations) are attracted to the cathode and negative io

Group 1 of the Periodic Table — lithium, sodium, potassium, rubidium, caesium and francium — forms a family of extremely reactive, soft metals that are all stored away from air and water. Th

The halogens are the reactive non-metals in Group 7: fluorine, chlorine, bromine and iodine. They have 7 outer electrons , exist as diatomic molecules , and become less reactive down the gro

The atmosphere is mainly nitrogen and oxygen , with small amounts of other gases. This chapter covers the composition of air , the properties and uses of the main gases, the greenhouse effec

The reactivity series orders metals by how readily they react. More reactive metals displace less reactive ones, react faster with water/acid, and need more energy to extract from their ores

Metals are extracted from their ores. The method depends on the metal's position in the reactivity series : unreactive metals occur native; metals below carbon are extracted by reduction wit

Acids produce H⁺ ions in water (pH < 7); alkalis produce OH⁻ ions (pH > 7). This chapter covers the pH scale, indicators, neutralisation , strong vs weak acids, and the titration method for

This chapter covers the reactions of acids (with metals, bases, carbonates) and the three methods for making salts : acid + excess insoluble solid, acid + alkali (titration), and precipitati

This chapter collects all the tests you must know: flame tests for metal ions, tests for cations (with sodium hydroxide and ammonia), tests for anions (carbonates, sulfates, halides, nitrate

Chemical reactions either release energy ( exothermic ) or absorb it ( endothermic ). This chapter covers the two reaction types, energy level diagrams , bond breaking and making , and how t

The rate of a reaction is how fast reactants turn into products. Rates increase with higher temperature, higher concentration, higher pressure (gases), bigger surface area , and catalysts .

Some reactions are reversible — they can go both ways. In a closed system they reach equilibrium , where the forward and backward reactions happen at the same rate. Le Chatelier's principle

Organic chemistry is the chemistry of carbon compounds . This chapter introduces the homologous series , the first series (alkanes), and the ideas of saturated/unsaturated , isomerism , and

Crude oil is a fossil fuel — a mixture of many hydrocarbons (mainly alkanes). It is separated by fractional distillation into fractions with different boiling points, each with its uses. Thi

Alkanes are saturated hydrocarbons (only single C–C bonds). They are found in crude oil and natural gas and are used mainly as fuels . This chapter covers their properties, combustion , and

Alkenes are unsaturated hydrocarbons containing a C=C double bond — their functional group. They are much more reactive than alkanes and are the starting materials for making polymers and ma

Alcohols have the functional group –OH and are made from alkenes (hydration) or by fermentation. They are used as fuels, solvents and in drinks. This chapter covers ethanol's structure, prop

Carboxylic acids contain the functional group –COOH . They are weak acids found in vinegar (ethanoic acid) and many foods. This chapter covers their structure, properties, reactions, and how

Esters are formed from a carboxylic acid + an alcohol (esterification). They have sweet, fruity smells and are used in flavourings, perfumes and as solvents . This chapter covers their forma

Polymers are very long molecules made of repeating units (monomers). This chapter covers addition polymers (from alkenes) and condensation polymers (polyesters, polyamides), the properties o