What is the difference between elements, compounds, and mixtures in the context of Cambridge IGCSE Coordinated Science?

In Cambridge IGCSE Coordinated Science, elements are pure substances consisting of only one type of atom. Compounds are substances formed when two or more elements chemically combine in fixed proportions. Mixtures, on the other hand, consist of two or more substances physically combined, where each substance retains its own properties and can be separated by physical means.

How can you distinguish between a compound and a mixture?

A compound has a fixed composition and properties that are different from its constituent elements, and it can only be separated into its elements by chemical reactions. A mixture, however, has a variable composition, retains the properties of its components, and can be separated into its components by physical methods such as filtration or distillation.

What are some examples of elements, compounds, and mixtures?

Examples of elements include oxygen (O), hydrogen (H), and gold (Au). Compounds include water (H2O), carbon dioxide (CO2), and sodium chloride (NaCl). Mixtures can be homogeneous, like air or saltwater, or heterogeneous, like a salad or a mixture of sand and iron filings.

Why is understanding elements, compounds, and mixtures important in Coordinated Science?

Understanding elements, compounds, and mixtures is crucial in Coordinated Science because it forms the foundation for studying chemical reactions, properties of materials, and the behavior of substances. This knowledge helps students comprehend how different substances interact and transform, which is essential for further studies in chemistry and related fields.

How do the properties of a compound differ from the properties of the elements that form it?

The properties of a compound are usually different from the properties of the elements that form it. For example, sodium is a highly reactive metal, and chlorine is a toxic gas, but when they combine to form sodium chloride (table salt), the compound is a stable, edible solid. This change in properties occurs because the elements chemically bond to form a new substance with its own unique characteristics.

Why is "Saying air is a compound because it contains oxygen and nitrogen" a common mistake in Elements, Compounds and Mixtures?

Why it happens: Students associate multiple types of atoms with 'compound' without checking whether they are chemically combined. How to avoid it: Air is a mixture: N₂ and O₂ are not chemically joined; their ratio varies; properties of each gas are retained.

Why is "Thinking any substance with a chemical formula is a compound" a common mistake in Elements, Compounds and Mixtures?

Why it happens: Elements like O₂ and P₄ have formulae but are not compounds — they are composed of one type of atom. How to avoid it: A compound must contain two or more DIFFERENT elements chemically combined (e.g. CO₂ = C + O; NaCl = Na + Cl).

Why is "Saying a compound can be separated by physical methods" a common mistake in Elements, Compounds and Mixtures?

Why it happens: Students confuse mixture separation (physical) with compound decomposition (chemical). How to avoid it: Compounds are separated by chemical reactions (e.g. electrolysis, thermal decomposition); mixtures by physical methods (filtration, distillation).

Atoms, Elements and CompoundsCambridge IGCSE Coordinated Sciences 0654

Elements, Compounds and Mixtures

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Elements, Compounds, and Mixtures — Cambridge IGCSE Coordinated Science 0654

All matter is classified as elements, compounds, or mixtures. Cambridge tests the definitions and the differences between compounds and mixtures in particular.

What you’ll learn

Mapped to the Cambridge IGCSE 0654 syllabus (2025-2027).

C3.2 — Define element, compound, and mixture.
C3.3 — Distinguish between compounds and mixtures.

Elements, Compounds, and Mixtures

The fundamental classification of all matter — know definitions and distinguishing features precisely.

Type	Definition	Separation	Example
Element	One type of atom only	Cannot be broken down chemically	Fe, O₂, Cu, N₂
Compound	Two+ elements chemically bonded in fixed ratio	Chemical methods only	H₂O, NaCl, CO₂, CuSO₄
Mixture	Two+ substances physically combined (no fixed ratio)	Physical methods (filtration, distillation)	Salt water, air, crude oil, alloys

Compound vs Mixture — key distinctions:

Feature	Compound	Mixture
Ratio of components	Fixed (by chemical formula)	Variable
Formation	Requires chemical reaction	Physical mixing only
Properties	Different from elements	Components retain own properties
Separation	Only by chemical methods	Physical methods (distillation, filtration, etc.)
Energy change	Yes (bonds formed/broken)	No (usually)

Example: Iron + sulfur mixture vs iron sulfide compound.

Mixture of Fe + S: iron filings can be removed by magnet; sulfur dissolves in CS₂; each element keeps its properties.
Iron(II) sulfide (FeS): cannot be separated by magnet; has different properties from iron or sulfur alone; requires chemical reaction to form.

Element: one atom type. Compound: elements chemically combined (fixed ratio). Mixture: physically combined (variable ratio).
Compounds have different properties from their elements. Mixture components keep their properties.
Mixtures separated by physical methods; compounds only by chemical reactions.

How it’s examined

Paper 2 MCQ: classify substances as element/compound/mixture from formulas or descriptions. Paper 4: 'Explain why air is a mixture and not a compound' (3 marks — variable composition, components keep properties, separated by physical methods, no energy change on mixing).

Sources: Cambridge IGCSE Coordinated Sciences 0654 syllabus 2025-2027 (C3); 0654 Examiner Reports 2022-2024. Last reviewed 2026-05-14.

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Step-by-step worked examples — Elements, Compounds and Mixtures

Step-by-step solutions to past-paper-style questions on elements, compounds and mixtures, written exactly the way a tutor would explain them at the board.

1Classifying substances
Core
Question
Classify each of the following as an element, compound, or mixture: copper, salt water, carbon dioxide, air.
Step-by-step solution
1. Step 1
  Copper (Cu): one type of atom only → element.
2. Step 2
  Salt water: sodium chloride dissolved in water; two substances not chemically combined, variable composition → mixture.
3. Step 3
  Carbon dioxide (CO₂): carbon and oxygen chemically combined in fixed ratio 1:2 → compound.
4. Step 4
  Air: mixture of N₂, O₂, Ar, CO₂, etc.; not chemically combined, composition varies → mixture.
Answer
Copper: element; salt water: mixture; carbon dioxide: compound; air: mixture.
2Differences between compound and mixture
Extended
Question
State TWO differences between a compound and a mixture.
Step-by-step solution
1. Step 1
  Composition: A compound has a fixed composition (elements combined in a definite ratio by mass); a mixture has variable composition.
2. Step 2
  Properties: A compound has new properties different from its constituent elements; a mixture retains the properties of its components.
3. Step 3
  Separation: A compound can only be separated by chemical reactions; a mixture can be separated by physical methods (filtration, distillation, etc.).
Answer
Compound: fixed composition, new properties, separated by chemical means. Mixture: variable composition, component properties retained, separated physically.
Examiner tip
Any two clear differences with both compound and mixture stated earn full marks.
3Why water is a compound, not a mixture of hydrogen and oxygen
Extended
Question
Explain why water is a compound and not a mixture of hydrogen and oxygen.
Step-by-step solution
1. Step 1
  In water (H₂O), hydrogen and oxygen are chemically combined in a fixed ratio of 2:1 by number of atoms.
2. Step 2
  Water has completely different properties from hydrogen (flammable gas) or oxygen (supports combustion); water does not burn and does not support combustion.
3. Step 3
  Water can only be separated into H₂ and O₂ by a chemical method (electrolysis), not a physical method.
Answer
Water has a fixed composition (H₂O), new properties different from H₂ and O₂, and can only be separated by chemical means (electrolysis) — all features of a compound, not a mixture.

Key Definitions and Keywords — Elements, Compounds and Mixtures

Definitions to memorise and the exact keywords mark schemes credit for elements, compounds and mixtures answers — sharpened from recent examiner reports for the 2026 0654 sitting.

Element
Examiner keyword
A pure substance made of only one type of atom; cannot be broken down into simpler substances by chemical means.
Compound
Examiner keyword
A substance formed when two or more elements are chemically combined in a fixed ratio; has properties different from its constituent elements; can only be separated by chemical reactions.
Mixture
Examiner keyword
Two or more substances that are not chemically combined; variable composition; retains the properties of its components; separated by physical methods.
Atom
The smallest particle of an element that can take part in a chemical reaction; cannot be broken down further by chemical means.
Molecule
Two or more atoms covalently bonded together; may be of the same element (e.g. O₂) or different elements (e.g. H₂O).

Common Mistakes and Misconceptions — Elements, Compounds and Mixtures

The traps other students keep falling into on elements, compounds and mixtures questions — taken from recent Cambridge IGCSE 0654 examiner reports and mark schemes — and how to avoid them.

✕Saying air is a compound because it contains oxygen and nitrogen
Why it happens
Students associate multiple types of atoms with 'compound' without checking whether they are chemically combined.
How to avoid it
Air is a mixture: N₂ and O₂ are not chemically joined; their ratio varies; properties of each gas are retained.
✕Thinking any substance with a chemical formula is a compound
Why it happens
Elements like O₂ and P₄ have formulae but are not compounds — they are composed of one type of atom.
How to avoid it
A compound must contain two or more DIFFERENT elements chemically combined (e.g. CO₂ = C + O; NaCl = Na + Cl).
✕Saying a compound can be separated by physical methods
Why it happens
Students confuse mixture separation (physical) with compound decomposition (chemical).
How to avoid it
Compounds are separated by chemical reactions (e.g. electrolysis, thermal decomposition); mixtures by physical methods (filtration, distillation).

Practice questions

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Past paper style quiz

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Elements, Compounds and Mixtures — frequently asked questions

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Elements, Compounds and Mixtures

Short Study Notes in the form of Slides

Short Study Notes — Elements, Compounds and Mixtures

Detailed Notes

What you’ll learn

How it’s examined

1Classifying substances

2Differences between compound and mixture

3Why water is a compound, not a mixture of hydrogen and oxygen

Element

Compound

Mixture

Atom

Molecule

✕Saying air is a compound because it contains oxygen and nitrogen

✕Thinking any substance with a chemical formula is a compound

✕Saying a compound can be separated by physical methods

Practice questions

Past paper style quiz

Assess your understanding

Elements, Compounds and Mixtures — frequently asked questions