All matter sorts into two piles: pure substances, which are elements or compounds, and mixtures, which are simply things put together.
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This single distinction is the most-asked idea in the chapter. Learn what separates each from the next.
🗂️ Telling them apart
| ELEMENT | COMPOUND | MIXTURE | |
|---|---|---|---|
| Made of | one kind of atom | two or more elements chemically joined | substances simply mixed |
| Ratio | — | fixed | any ratio |
| Separated by | cannot be split by chemical means | chemical means only | physical means |
| Properties | its own | quite different from its elements | those of its parts |
| Examples | gold, oxygen, iron | water, salt, carbon dioxide | air, milk, soil |
The classic example: hydrogen burns and oxygen supports burning — yet water, made of both, puts fires out. A compound has completely new properties. A mixture would keep the old ones.
The quickest test: can you separate it by a physical method — filtering, magnets, evaporation, picking it out? Then it is a mixture. If only a chemical reaction will split it, it is a compound.
Elements divide into metals and non-metals, and their properties are almost opposites.
🔩 Opposite in almost every way
| Property | METALS | NON-METALS |
|---|---|---|
| Appearance | shiny (lustrous) | dull |
| Conducting | good conductors | poor conductors |
| Hammering | malleable — sheets | brittle, break easily |
| Drawing | ductile — wires | not ductile |
| Sound | sonorous — they ring | not sonorous |
| At room temp | solid (except mercury) | solid, liquid or gas |
Three exceptions the exam loves. Mercury is a metal that is liquid at room temperature. Graphite is a non-metal that conducts electricity. Sodium and potassium are metals so soft you can cut them with a knife.
Every method uses a difference between the parts — in size, in magnetism, in boiling point.
⚗️ Which method, and why
| Method | Uses the difference in | Example |
|---|---|---|
| Filtration | particle size | sand from water |
| Evaporation | boiling point | salt from sea water |
| Magnetic separation | magnetism | iron filings from sand |
| Sieving | size | flour from bran |
| Winnowing | weight in air | husk from grain |
| Distillation | boiling point | pure water from salty water |
| Sedimentation and decantation | density | muddy water settling |
Evaporation or distillation? Evaporation keeps the solid and lets the liquid escape. Distillation keeps both — the vapour is cooled and collected. If a question wants the pure water back, the answer is distillation.
12 questions on elements, compounds and mixtures. 🍀
