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Chapter 3

Diversity of Matter by its Chemical Composition

Everything around you is one of three things — an element, a compound, or a mixture. Six lessons, six labs, one chapter map, and thirty questions.

The one idea behind the whole chapter

The chapter asks four questions in turn — why composition matters, what elements and compounds are, what mixtures are, and how to tell all three apart. But every one of them comes back to a single sorting decision:

Ask this of any substance Is it one kind of atom? → element.
Two or more kinds, chemically joined in a fixed ratio? → compound.
Two or more substances just sharing space, in any ratio? → mixture.

Get that decision right and the rest — solutions, suspensions, the air, steel, seawater — are just examples of the third box.

This is scoped for G3. The textbook marks Solubility as optional for G2; for you it is core, and it is the part most likely to be examined precisely because it is the part people skip.

3.1 · Why does composition matter?

Lesson 1

Why composition matters

Melamine plates and melamine milk powder. Recycling bins and e-waste. Same substance, different verdict.

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3.2 · Elements and compounds

Lesson 2

Elements

The 118 building blocks, the Periodic Table, metals and non-metals — with an explorer you can click through.

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Lesson 3

Compounds

Chemically combined, fixed proportions, new properties, hard to separate — seen at the particle level.

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3.3 · Mixtures

Lesson 4

Mixtures

Air, steel, seawater, milk. Build your own mixture and see what kind it is.

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Lesson 5

Solutions, dissolving and solubility

Solute and solvent, dilute and concentrated, how fast versus how much. Two labs.

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Lesson 6

Suspensions, and telling everything apart

The torch test, the settling test, and Table 3.3 — the three questions that separate element, compound and mixture.

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Revise and practise

Revision

The whole chapter on one page

Every definition, all three comparison tables, the composition of air and the factors lists.

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Practice

30 interactive questions

Sorting, labelling particle diagrams, typed answers, structured questions — every wrong answer explains itself.

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Challenging · Lvl 2

Challenging Qns Lvl 2

Twenty harder questions with the options set deliberately close together — only correct reasoning separates them.

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