How to use this guide
- Open each topic and read the key facts.
- Use the flashcards to memorise core definitions/tests.
- Do the quick quiz + drag-drop matching in the Practice Zone.
- Use the Online Resources at the bottom for videos, notes, and sims.
Notes Class activity
P2 & P4 Class Activity — Test for Ions
Use this interactive activity to practise qualitative analysis (cation/anion tests) and exam-style interpretation.
Atoms, Elements & Isotopes Core
Key definitions
- Atom: smallest particle of an element that can exist.
- Element: made of one type of atom only.
- Molecule: two or more atoms chemically bonded together.
- Isotope: same protons, different neutrons.
Must-know facts
- Proton number defines the element.
- Isotopes have different mass numbers because neutrons differ.
- Atoms of the same element do not all have the same mass (isotopes).
- Molecules can be of the same element (e.g. O₂) or different elements (e.g. CO₂).
If only the number of neutrons changes → different isotope.
Electronic Structure & Ions Core
Electron shells (IGCSE)
Electrons fill shells: 2, 8, 8 (for the first 20 elements at IGCSE level).
Example: sodium (11) → 2,8,1
Forming ions
- Cation (+): formed when an atom loses electrons.
- Anion (−): formed when an atom gains electrons.
- Protons never change in chemical reactions.
Example: Na⁺ has 11 protons and 10 electrons.
Bonding Core
| Bond type | Between | Examples |
|---|---|---|
| Ionic | Metal + non-metal | NaCl, MgO |
| Covalent | Non-metal + non-metal | H₂O, CO₂, O₂ |
| Metallic | Metals | Cu, Fe, Al |
Carbon dioxide (CO₂)
CO₂ is made from non-metals, so it has covalent bonding.
Reactions (Oxidation & Reduction) Core
Definitions
- Oxidation = loss of electrons
- Reduction = gain of electrons
- Redox means both happen in the same reaction
Typical redox example
metal oxide + carbon → metal + carbon dioxide
The metal oxide is reduced (oxygen removed / gains electrons) and carbon is oxidised.
Energetics (Temperature Change) Core
| Type | What happens to temperature? | Key idea |
|---|---|---|
| Exothermic | Temperature increases | Energy released to surroundings |
| Endothermic | Temperature decreases | Energy taken in from surroundings |
How to prove exothermic in a practical
Measure temperature before mixing, then after mixing. A rise in temperature shows it is exothermic.
Acids, Alkalis & Salts Core
Neutralisation (general equation)
acid + alkali → salt + water
Name of reaction: neutralisation (often exothermic).
pH values to memorise
| Liquid | Typical pH |
|---|---|
| Strong acid (e.g. dilute hydrochloric acid) | 1 |
| Neutral (water) | 7 |
| Strong alkali (e.g. potassium hydroxide) | 13 |
Example product naming
hydrochloric acid + potassium hydroxide → potassium chloride + water
The salt name comes from the metal in the alkali and the acid anion (e.g. chloride from HCl).
Rates of Reaction Core
Factors that increase rate
- Temperature ↑
- Concentration ↑
- Surface area ↑ (powdered solid)
Best way to measure a gas-producing reaction
Measure the volume of gas produced every minute (volume per unit time).
Tests for Gases High yield
| Gas | Test | Positive result |
|---|---|---|
| Hydrogen | Lighted splint | Squeaky pop |
| Oxygen | Glowing splint | Relights |
| Carbon dioxide | Limewater | Turns milky |
| Ammonia | Damp red litmus paper | Turns blue |
| Chlorine | Damp litmus paper | Bleaches white |
Note: chlorine bleaches litmus only when damp.
Qualitative Analysis (Ions) High yield
Copper(II) ions (Cu²⁺)
- With sodium hydroxide: light blue precipitate, insoluble in excess
- With ammonia: light blue precipitate, soluble in excess → dark blue solution
Zinc ions (Zn²⁺)
- With sodium hydroxide: white precipitate, soluble in excess
- With ammonia: white precipitate, insoluble in excess
Ammonium ions (NH₄⁺) test
Add sodium hydroxide, warm gently → ammonia gas produced → turns damp red litmus blue.
Separation Techniques Core
| Mixture | Method |
|---|---|
| Solid + liquid | Filtration |
| Salt solution → crystals | Evaporation / Crystallisation |
| Liquid from solution | Simple distillation |
| Two miscible liquids | Fractional distillation |
Electrolysis Basics Core
Cathode vs Anode
- Cathode (−): reduction (gain of electrons)
- Anode (+): oxidation (loss of electrons)
Aluminium extraction idea
Aluminium forms at the cathode. Oxygen forms at the anode.
Air Composition & Combustion Core
| Gas | Percentage |
|---|---|
| Nitrogen | 78% |
| Oxygen | 21% |
| Carbon dioxide | 0.04% |
| Other gases | small amount |
Key idea
Processes like respiration and many types of combustion use oxygen and produce carbon dioxide.
Fertilisers (NPK) Core
Essential elements in fertilisers
The key fertiliser elements are Nitrogen (N), Phosphorus (P), and Potassium (K). Mnemonic: NPK.
Practice Zone (Self-check) Interactive
Quick Quiz (tap an option)
Gas Tests Matching (Drag & Drop)
Drag each test/result to the correct gas. Then press “Check”.
Online Resources (Trusted) Links
Notes & Revision
Use these for clear summaries and exam-style explanations.
Simulations & Videos
Use PhET for concepts (rates, particles) and FuseSchool for short revision videos.