Pearson Edexcel · IGCSE · 4CH1
Chemistry — Keywords & Key Terms — Definitions Glossary (2026)
Pearson Edexcel International GCSE Chemistry (4CH1)
Topic-by-topic keywords, key terms and definitions for precise exam language—separate from our revision checklists (topic coverage) and formula sheets (equations).
Keywords & Key Terms — definitions
Examiner-style keywords and definitions organised by syllabus topic. Terms are tagged Essential (start here), Core (typical exam standard), and Advanced for harder distinctions — tick each row when you can recall it. Your progress is saved in this browser for this list.
Pearson Edexcel IGCSE Chemistry (4CH1)
Pearson Edexcel IGCSE Chemistry (4CH1)
Pearson Edexcel International GCSE Chemistry (4CH1)
Topic groups follow Pearson Edexcel International GCSE Chemistry (4CH1) for 2026: principles of chemistry, inorganic, physical chemistry, organic, and resources.
Mark schemes: Balanced equations with correct state symbols when asked. Observation answers need specific detail. Explanations should use bonding and particle ideas from the specification.
Active recall: 0 / 68 terms ticked
| Recalled | Topic | Level | Keyword | Definition |
|---|---|---|---|---|
| Subatomic particles & atomic structure | Essential | Proton | Particle in the nucleus with relative mass 1 and charge +1. | |
| Subatomic particles & atomic structure | Essential | Neutron | Particle in the nucleus with relative mass 1 and charge 0. | |
| Subatomic particles & atomic structure | Essential | Electron | Particle outside nucleus; very small mass; charge −1. | |
| Subatomic particles & atomic structure | Core | Nucleus | Tiny dense centre of the atom containing protons and neutrons. | |
| Subatomic particles & atomic structure | Core | Atomic number | Number of protons in an atom — defines the element. | |
| Subatomic particles & atomic structure | Core | Mass number | Total number of protons and neutrons in one nucleus. | |
| Subatomic particles & atomic structure | Core | Isotope | Atoms of the same element with different numbers of neutrons. | |
| Subatomic particles & atomic structure | Core | Electron shells / energy levels | Regions around the nucleus where electrons are found. | |
| Subatomic particles & atomic structure | Essential | Element | Substance made of only one type of atom. | |
| Subatomic particles & atomic structure | Essential | Compound | Substance formed when two or more elements chemically combine. | |
| Subatomic particles & atomic structure | Advanced | Relative atomic mass (Ar) | Weighted mean mass of an element’s isotopes on the carbon-12 scale. | |
| Bonding, structure & materials | Core | Periodic table | Elements ordered by atomic number; periods and groups. | |
| Bonding, structure & materials | Core | Group | Column — same number of outer-shell electrons in main groups. | |
| Bonding, structure & materials | Core | Period | Row — same number of occupied shells. | |
| Bonding, structure & materials | Core | Ionic bonding | Transfer of electrons from metal to non-metal — ions in a giant lattice. | |
| Bonding, structure & materials | Core | Covalent bonding | Sharing electron pairs between non-metal atoms. | |
| Bonding, structure & materials | Core | Metallic bonding | Positive ions in a sea of delocalised electrons. | |
| Bonding, structure & materials | Core | Ion | Charged atom or group of atoms after electron transfer. | |
| Bonding, structure & materials | Core | Molecule | Group of atoms bonded covalently. | |
| Bonding, structure & materials | Advanced | Giant ionic lattice | Regular arrangement of alternating positive and negative ions. | |
| Bonding, structure & materials | Advanced | Simple molecular | Small molecules with weak forces between molecules. | |
| Bonding, structure & materials | Advanced | Giant covalent | Many atoms covalently bonded in a lattice (e.g. diamond, graphite). | |
| Bonding, structure & materials | Advanced | Intermolecular forces | Weak forces between molecules — London forces, dipole–dipole. | |
| Quantitative chemistry | Core | Relative formula mass (Mr) | Sum of relative atomic masses in a formula unit. | |
| Quantitative chemistry | Core | Mole | Amount containing the Avogadro constant (6.02 × 10²³) of particles. | |
| Quantitative chemistry | Core | Molar mass | Mass of one mole of substance in g/mol. | |
| Quantitative chemistry | Core | Empirical formula | Simplest whole-number ratio of atoms. | |
| Quantitative chemistry | Core | Molecular formula | Actual numbers of atoms in one molecule. | |
| Quantitative chemistry | Advanced | Titration | Volumetric method to find unknown concentration using a burette and indicator. | |
| Quantitative chemistry | Core | Concentration | Moles of solute per dm³ of solution (mol/dm³). | |
| Quantitative chemistry | Core | Gas volume | Molar volume at room temperature and pressure (context given in exams). | |
| Quantitative chemistry | Core | Percentage yield | Actual yield ÷ theoretical yield × 100%. | |
| Quantitative chemistry | Core | Atom economy | Mass of desired product ÷ mass of all reactants × 100%. | |
| Chemical reactions & energy | Essential | Exothermic / endothermic | Overall energy transfers heat to surroundings / takes in from surroundings. | |
| Chemical reactions & energy | Core | Rate of reaction | Change in concentration or mass per unit time. | |
| Chemical reactions & energy | Core | Catalyst | Increases rate; not used up in overall equation; alternative pathway. | |
| Chemical reactions & energy | Advanced | Reversible reaction | Products can reform reactants in a closed system. | |
| Chemical reactions & energy | Core | Dynamic equilibrium | Forward and reverse rates equal. | |
| Chemical reactions & energy | Core | Le Chatelier’s principle | If a change is imposed, equilibrium shifts to partially counteract it. | |
| Chemical reactions & energy | Core | Oxidation | Loss of electrons (or gain of oxygen in many contexts). | |
| Chemical reactions & energy | Core | Reduction | Gain of electrons (or loss of oxygen). | |
| Chemical reactions & energy | Core | Reactivity series | Metals ordered by reactivity — predicts displacement. | |
| Acids, bases, salts & electrolysis | Essential | Acid | pH below 7; forms H⁺(aq) in water. | |
| Acids, bases, salts & electrolysis | Core | Alkali | Soluble base; pH above 7. | |
| Acids, bases, salts & electrolysis | Core | Base | Neutralises an acid. | |
| Acids, bases, salts & electrolysis | Core | pH | Logarithmic measure of acidity/alkalinity. | |
| Acids, bases, salts & electrolysis | Core | Salt | Ionic compound produced from acid + base. | |
| Acids, bases, salts & electrolysis | Core | Neutralisation | Acid + base → salt + water. | |
| Acids, bases, salts & electrolysis | Advanced | Electrolysis | Breakdown of ionic compound by electricity — cations to cathode, anions to anode. | |
| Acids, bases, salts & electrolysis | Core | Cathode | Negative electrode — reduction. | |
| Acids, bases, salts & electrolysis | Core | Anode | Positive electrode — oxidation. | |
| Acids, bases, salts & electrolysis | Core | Electrolyte | Ion-containing melt or solution that conducts. | |
| Separating mixtures & analysis | Core | Filtration | Separate insoluble solid from liquid. | |
| Separating mixtures & analysis | Core | Distillation | Separate solvent from solution by boiling and condensing. | |
| Separating mixtures & analysis | Core | Fractional distillation | Separate liquids with different boiling points. | |
| Separating mixtures & analysis | Core | Chromatography | Separate mixture dissolved in a solvent on paper or column. | |
| Separating mixtures & analysis | Core | Rf value | Distance moved by substance ÷ distance moved by solvent. | |
| Organic chemistry basics | Essential | Hydrocarbon | Contains only carbon and hydrogen. | |
| Organic chemistry basics | Core | Alkane | Saturated — only single bonds; CₙH₂ₙ₊₂. | |
| Organic chemistry basics | Core | Alkene | Contains C=C; CₙH₂ₙ. | |
| Organic chemistry basics | Core | Alcohol | Contains –OH functional group. | |
| Organic chemistry basics | Core | Carboxylic acid | Contains –COOH. | |
| Organic chemistry basics | Advanced | Functional group | Atom or group that determines characteristic reactions. | |
| Organic chemistry basics | Core | Homologous series | Family with same functional group and trend in properties. | |
| Organic chemistry basics | Core | Cracking | Break long hydrocarbons into shorter, more useful molecules. | |
| Organic chemistry basics | Core | Addition polymer | Unsaturated monomers add across double bonds to form polymer. | |
| Organic chemistry basics | Core | Combustion | Fuel + oxygen; complete combustion of hydrocarbons → CO₂ + H₂O. | |
| Organic chemistry basics | Core | Structural isomer | Same molecular formula, different structure. |
Pair this with our revision checklists, formula sheets hub and past paper finder.
Chemistry (4CH1) — Keywords & Key Terms FAQ
- What is on this Pearson Edexcel IGCSE Chemistry keywords and key terms list?
- It is a topic-organised glossary of important chemistry terms with short, exam-style definitions aligned to Pearson Edexcel International GCSE Chemistry (4CH1) (4CH1). It is designed for “define”, “state”, “outline” and “explain” questions where precise vocabulary earns marks.
- How should I use this Chemistry glossary alongside past papers?
- Tick terms when you can recall them without reading the answer, then check your wording against mark schemes. Pair vocabulary practice with past papers for IGCSE Chemistry (4CH1) so you apply terms in context.
- Is this the same as a revision checklist or a formula sheet?
- No. Revision checklists help you track which syllabus topics you have covered and your confidence—separate pages on Tutopiya. Formula sheets summarise equations and quantitative relationships. This page is only a definitions and key-terms glossary for Chemistry. Quantitative relationships belong on formula sheets; this list emphasises language and concepts.
- Can I download this Chemistry keywords and key terms list for free?
- Yes. After a quick free sign-up you can download a UTF-8 CSV (opens in Excel or Google Sheets) or open a print-friendly page and save as PDF. Browsing the list on the page is free.
- Is this Chemistry list aligned to the 4CH1 specification?
- Topic groupings and wording follow Pearson Edexcel International GCSE Chemistry (4CH1) for Pearson Edexcel IGCSE. Always confirm final learning objectives and any regional options in your official specification and recent examiner reports for your exam session.
- Why focus on definitions instead of full notes?
- Mark schemes reward correct technical terms and clear links between ideas. A compact glossary lets you drill the exact language examiners expect for Chemistry at IGCSE, separate from longer notes or topic trackers.