Cambridge IGCSE Chemistry 0620 – Unit Summaries

Free overview of every unit in the Cambridge IGCSE Chemistry (0620) syllabus, written by Dr. Khaled Dabour for Dabour Hub students. Each unit below starts with the key ideas you need to know. The complete revision notes, diagrams, quizzes and question banks are available to registered students.

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1. States of matter – IGCSE Chemistry 0620

The three states Changes of state, both directions Evaporating is not boiling. Evaporation happens at any temperature, only at the surface, and only the fastest particles escape – which is why the liquid left behind cools. Boiling happens at one fixed temperature, throughout the liquid, with bubbles forming inside it. During a change of state the temperature stays constant on a heating curve, because the…

2. Atoms, elements and compounds – IGCSE Chemistry 0620

Inside the atom Proton number is the number of protons and defines the element. Nucleon number is protons plus neutrons. Neutrons = nucleon number − proton number. Isotopes are atoms of the same element with the same proton number but different numbers…

3. Stoichiometry – IGCSE Chemistry 0620

The quantities The route, every time Write the balanced equation. Convert what you are given into moles. Use the ratio from the equation to get moles of what you want. Convert those moles back into mass, volume or concentration. Step 3 is the only chemistry; the rest is arithmetic. Most lost marks come from skipping step 1. Limiting reactant Work out the moles of each reactant and divide each by its…

4. Electrochemistry – IGCSE Chemistry 0620

The words Remember it as OIL RIG (oxidation is loss, reduction is gain) and PANIC (positive is anode, negative is cathode). Which ion is discharged in solution At the cathode: the less reactive of the metal ion and hydrogen is discharged. So copper, silver and lead give the metal; sodium, potassium, calcium and magnesium give hydrogen instead. At the anode: if a halide ion is present in reasonable concentration it…

5. Chemical energetics – IGCSE Chemistry 0620

The two kinds of reaction The energy profile The curve starts at the reactants, climbs to a peak and ends at the products. The climb is the activation energy – the minimum energy needed for a reaction to occur. The difference between the two ends is ΔH, the enthalpy change. A catalyst gives an alternative route with a lower activation energy, so the peak is lower. It…

6. Chemical reactions – IGCSE Chemistry 0620

Rate of reaction Reactions happen when particles collide with enough energy – the activation energy – and in the right orientation. Anything that raises the frequency of successful collisions raises the rate. Temperature is the only factor that changes both the number of collisions and their energy – that is why it has such a large effect. Reading a rate graph: the steeper the curve, the faster the rate. The curve flattens…

7. Acids, bases and salts – IGCSE Chemistry 0620

Definitions Indicator colours The four acid reactions Which acid gives which salt Hydrochloric acid gives chlorides, sulfuric acid gives sulfates, nitric acid gives nitrates, phosphoric acid gives phosphates. Choosing the preparation method Solubility rules worth…

8. The Periodic Table – IGCSE Chemistry 0620

How it is arranged Elements are in order of increasing proton number. A group is a vertical column – the same number of outer electrons, so similar chemistry. A period is a horizontal row – the same number of shells. Group I, the alkali metals All are soft, shiny when cut but tarnish quickly, and react with water to give a hydroxide plus hydrogen. Lithium fizzes steadily, sodium melts into a ball and…

9. Metals – IGCSE Chemistry 0620

The reactivity series Potassium, sodium, calcium, magnesium, aluminium, (carbon), zinc, iron, (hydrogen), copper, silver, gold. A more reactive metal displaces a less reactive one from its compound – that displacement is the evidence for the order. Why the method of extraction follows the series The more reactive the metal, the more stable its compound and the harder it is to reduce. Metals above carbon must be extracted by electrolysis; those below it can be reduced by carbon, which is far cheaper. The…

10. Chemistry of the environment – IGCSE Chemistry 0620

Water Treatment of the public supply: sedimentation and filtration remove solids, then chlorination kills bacteria. Distilled water is needed in chemistry because dissolved salts would interfere with the reaction. Air Clean dry air is about 78% nitrogen, 21% oxygen, and small amounts of argon and carbon dioxide. Catalytic converter: 2CO + 2NO → 2CO₂ +…

11. Organic chemistry – IGCSE Chemistry 0620

The families A homologous series is a family with the same general formula and functional group, differing by CH₂, with similar chemistry and a gradual trend in physical properties. The first four stems: meth- (1 carbon), eth- (2), prop- (3), but- (4). Alkanes and alkenes compared Reactions to know Complete combustion: hydrocarbon + plenty of oxygen → carbon dioxide + water. Incomplete combustion: limited oxygen…

12. Experimental techniques and chemical analysis – IGCSE Chemistry 0620

Choosing a separation method Chromatography Draw the baseline in pencil, because ink would dissolve and run. Keep the baseline above the solvent level so the spots are not washed off. Rf = distance moved by the spot ÷ distance moved by the solvent front. It is always between 0 and 1…