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Elements, Compounds & Mixtures

How all matter is either a pure substance — an element or a compound — or a mixture, and how the parts of a mixture can be separated.

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What this chapter covers

  1. Pure Substances and Mixtures

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    • Classification of MatterPure substances or homogeneous, heterogeneous mixtures.
    • Substance vs MixtureFixed formula versus variable ratio.
    • Metals Nonmetals MetalloidsElements sub-classified, like Cu, S, Si.

  2. Element

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    • DefinitionOnly one type of atom.
    • Characteristics of ElementsNatural or artificial; atom keeps properties.

  3. Compound

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    • DefinitionElements chemically combined in fixed proportion.
    • Characteristics of CompoundsHomogeneous; properties differ from constituents.

  4. Mixture

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    • DefinitionSubstances mechanically mixed in any proportion.
    • Characteristics of a MixtureComponents keep their original properties.
    • Types of MixturesHomogeneous or heterogeneous, elements and compounds.

  5. Separation Methods

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    • OverviewRemove unwanted components to get purity.
    • Solid-Solid MixturesHand-picking by size, colour; magnets.
    • Solid-Liquid MixturesFiltration, decantation, evaporation and distillation.
    • Liquid-Liquid MixturesSeparating funnel or fractional distillation.
    • Liquid-Gas MixturesHeating drives out dissolved gas.
    • Gas-Gas MixturesPreferential liquefaction, dissolution, fractional evaporation.
    • FiltrationInsoluble solid caught by filter.
    • Sedimentation and DecantationSettle heavy particles, pour off liquid.
    • Evaporation and CrystallisationEvaporate solvent, leaving dissolved solid.
    • Separating FunnelImmiscible liquids separate by density.
    • DistillationVaporise then condense; recover both.
    • Fractional DistillationMiscible liquids; lowest boiling distils first.
    • SublimationSolid to vapour, back to solid.
    • ChromatographyDyes separate by different adsorption rates.
    • Separating Multi-component MixturesApply methods in sequence, like gunpowder.

Try a sample question

Which of the following solids sublimes at ordinary room temperature?

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