O Level/IGCSE Chemistry Definitions List (All Chapters) – Updated & Exam-Focused (2025)
Last Updated: 29 November 2025 • 15:07
This is the most concise, exam-centered, high-accuracy O Level/IGCSE Chemistry Definitions List (all chapters, 0620/5070 syllabus aligned).
Ideal for quick revision, last-day prep, formula memorization, and chemistry worksheets (PDF ready).
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📘 Complete O Level & IGCSE Chemistry Definitions (ALL Chapters)
1. **Experimental Chemistry**
- Accuracy: How close a measurement is to the true value.
- Precision: Reproducibility of repeated measurements.
- Reliability: Consistency of results under identical conditions.
- Filtration: Separation of an insoluble solid from a liquid.
- Distillation: Separating liquids using different boiling points.
- Chromatography: Separation based on different solubilities and adsorption.
Download: Chemical Formula Worksheet PDF | Understanding Chemical Formulas PDF
2. **Particle Theory & States of Matter**
- Element: Substance made of one type of atom.
- Compound: Two or more elements chemically combined.
- Mixture: Substances physically combined.
- Brownian Motion: Random movement of particles due to collisions.
- Diffusion: Spreading of particles from a high to low concentration.
Resources: Chemistry Formula Sheet High School | Chemical Formula Notes PDF
3. **Atomic Structure & Periodic Table**
- Proton Number: Number of protons (atomic number).
- Nucleon Number: Total protons + neutrons.
- Isotopes: Atoms of the same element with different neutron numbers.
- Group: Vertical column showing same number of outer electrons.
- Period: Horizontal row showing number of electron shells.
See also: Formula Sheet for Structure of Atom | Chemistry Book PDF High School
4. **Ions, Bonding & Structures**
- Ionic Bonding: Transfer of electrons forming oppositely charged ions.
- Covalent Bonding: Sharing of electron pairs between atoms.
- Metallic Bonding: Positive ions in a sea of delocalized electrons.
- Giant Ionic Structure: Lattice of alternating positive and negative ions.
- Giant Covalent Structure: Strong covalent bonds throughout (diamond/silicon dioxide).
Cheat Sheets: Ionic Formula Sheet | Ion Formula Sheet
5. **Stoichiometry & Chemical Calculations**
- Mole: Amount of substance containing Avogadro number of particles.
- Molar Mass: Mass of 1 mole of substance.
- Empirical Formula: Simplest whole-number ratio of atoms.
- Molecular Formula: Actual number of atoms per molecule.
- Concentration: Amount of solute per unit volume.
Download: O'Level Chemistry Moles Formula Sheet | Molecular Formula Worksheet PDF | General Chemistry Formula Sheet PDF
6. **Chemical Energetics**
- Exothermic Reaction: Releases heat energy.
- Endothermic Reaction: Absorbs heat energy.
- Activation Energy: Minimum energy needed for reaction.
- Bond Energy: Energy needed to break 1 mole of bonds in gaseous state.
Related: Chemistry Formula Reference Sheet
7. **Rates of Reaction**
- Rate of Reaction: Change in concentration per unit time.
- Catalyst: Speeds up reaction without being consumed.
- Collision Theory: Particles must collide with sufficient energy and correct orientation.
8. **Reversible Reactions & Equilibrium**
- Reversible Reaction: Can proceed both forward and backward.
- Dynamic Equilibrium: Forward and backward rates equal.
- Le Chatelier’s Principle: System shifts to oppose applied change.
9. **Acids, Bases & Salts**
- Acid: Proton donor.
- Base: Proton acceptor.
- Alkali: Soluble base releasing OH⁻ ions.
- Neutralisation: Reaction of acid with base forming salt + water.
Printable: Chemical Formula Worksheet 8th Grade
10. **Redox & Electrolysis**
- Oxidation: Gain of oxygen / loss of electrons.
- Reduction: Loss of oxygen / gain of electrons.
- Electrolysis: Decomposition using electricity.
- Anode: Positive electrode.
- Cathode: Negative electrode.
Extras: P Chem Formula Sheet | Chem 1 Formula Sheet
11. **Periodic Trends & Reactivity**
- Displacement Reaction: More reactive element replaces less reactive one.
- Transition Metals: Form coloured compounds, multiple oxidation states.
12. **Organic Chemistry**
- Homologous Series: Family of compounds with same functional group.
- Isomerism: Same molecular formula, different structural formula.
- Cracking: Breaking large hydrocarbons into smaller ones.
- Addition Reaction: One molecule adds across a double bond.
- Substitution Reaction: Atom/group replaced by another.
Downloads: Organic Chemistry Cheat Sheet PDF Free | Organic Chemistry Types of Formulas
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🌟 Final Exam Tip
Cambridge examiners reward exact phrases. Memorize the definitions above word-for-word and practice with the free formula-sheet PDFs linked throughout this article.



















