O Level/IGCSE Chemistry Definitions List (All Chapters) – Updated, Exam-Centered & Easy
Updated: 29 November, 2025 – 15:03
This is the most concise, exam-focused, and student-friendly O Level & IGCSE Chemistry Definitions List covering every chapter, aligned with CAIE Syllabus 5070 & 0620. Perfect for crash revision, quick tests, and final preparation.
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📘 O Level / IGCSE Chemistry Definitions (All Chapters)
These definitions are concise, examiner-friendly, and updated for CAIE O Level 5070 & IGCSE 0620.
Chapter 1: Experimental Chemistry
- Atom: The smallest particle of an element that retains its properties.
- Molecule: Two or more atoms chemically bonded together.
- Mixture: A combination of substances not chemically bonded.
- Solution: A homogeneous mixture of solute in solvent.
- Filtration: Separation using a porous barrier to remove insoluble solids.
- Crystallisation: Formation of pure crystals from a saturated solution.
Chapter 2: Particulate Nature of Matter
- Diffusion: Movement of particles from high to low concentration.
- Brownian Motion: Random movement of particles due to collision.
Chapter 3: Atomic Structure
- Isotopes: Atoms of the same element with same proton number but different neutron number.
- Relative Atomic Mass (Ar): Average mass of isotopes compared to C-12.
- Ions: Charged particles formed by gaining or losing electrons.
Chapter 4: Chemical Bonding
- Ionic Bond: Electrostatic attraction between oppositely charged ions.
- Covalent Bond: Sharing of electron pairs between atoms.
- Metallic Bond: Attraction between positive ions and delocalised electrons.
Chapter 5: Stoichiometry
- Mole: Amount containing 6.02 × 10²³ particles.
- Molar Volume: Volume of 1 mole of gas (24 dm³ at RTP).
- Empirical Formula: Simplest whole-number ratio of atoms.
Chapter 6: Electricity & Chemistry
- Electrolysis: Decomposition using electricity.
- Anode: Positive electrode.
- Cathode: Negative electrode.
- Electrolyte: Ionic substance conducting when molten or aqueous.
Chapter 7: Energetics
- Exothermic: Releases heat.
- Endothermic: Absorbs heat.
- Activation Energy: Minimum energy required for successful collisions.
Chapter 8: Rates of Reaction
- Rate: Change in concentration per unit time.
- Catalyst: Speeds up reaction without being consumed.
Chapter 9: Acids, Bases & Salts
- Acid: Proton donor.
- Base: Proton acceptor.
- Alkali: Soluble base producing OH⁻ ions.
- Neutralisation: Acid + Base → Salt + Water.
Chapter 10: Periodic Table
- Group: Vertical column showing similar properties.
- Period: Horizontal row showing increasing proton number.
Chapter 11: Metals
- Alloy: Mixture of metals improving strength.
- Corrosion: Gradual oxidation of metals.
Chapter 12: Air & Atmosphere
- Pollutant: Substance harmful to environment.
- Greenhouse Effect: Warming due to trapped infrared radiation.
Chapter 13: Organic Chemistry
- Homologous Series: Same functional group, similar properties, same general formula.
- Isomerism: Same molecular formula but different structures.
- Cracking: Breaking large hydrocarbons into smaller molecules.
⏳ Timeline to Finish Chemistry Syllabus
- Week 1–2 → Experimental Chemistry + Particles + Formulae
- Week 3–4 → Bonding + Periodic Table
- Week 5–6 → Stoichiometry + Energy + Rates
- Week 7–8 → Acids + Bases + Salts
- Week 9–10 → Organic Chemistry + Finals Revision
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