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  • Elements, Compounds and Mixtures.Chapter 16

  • Classification of SubstancesElementsMoleculesCompoundsMixtures.

  • ElementsElements are substances made up of only one type of atom.Example Hydrogen, Gold.

  • Periodic Table of Elements

  • Molecule A molecule is made up of two or more atoms chemically combined.

  • CompoundsCompounds are made up of two or more different types of atoms chemically combined.

  • Properties of CompoundsWhen a compound is formed during a chemical reaction its properties differ from those of the elements from which it is made.Example: Water is made from hydrogen and oxygen.Hydrogen flammable gasOxygen colourless gas.

  • Diagram of Salt, water, sucrose.

  • MixturesA mixture consists of two or more different substances mingled together but not chemically combined.Examples:Sea water and saltAir nitrogen, oxygen Soil sand, clay, humus

  • Compare mixtures and Compounds.

  • MixtureCompoundThe amounts of the substances in the mixture can vary.The elements in a compound are always present in the same fixed proportion.A mixture contains two or more substancesA compound is a single substance.The properties of a mixture are similar to those of the substances in a mixture.The properties of a compound are different to those of the elements which reacted to form it.There are practically no energy changes when a mixture is madeHeat is usually given out or taken in when a compound is formed.It is usually easy to separate the components of a mixture.It is usually difficult to separate the components of a compound.

  • iron particlesKey:strong bonds between iron particles one iron particleiron particles held together by strong bonds

  • iron particles iron particles are attracted to a magnetiron particles diagram

  • sulfur particlesKey:strong bonds between sulfur particles one sulfur particlesulfur particles held together by strong bonds

  • sulfur particlessulfur particles are not attracted to a magnetsulfur particles diagram

  • iron particles

  • A mixture of iron and sulfur particlesstrong bonds between sulfur particles strong bonds between iron particlesWhats this?

  • A mixture of iron and sulfur particlesA magnet attracts the iron particles but not the sulfur particles.The mixture is separatedmixture diagram

  • one sulfur particle one iron particlestrong bonds between iron and sulfur particlesWhats this?A compound between iron and sulfur particles

  • strong bonds between iron and sulfur particlesA compound between iron and sulfur particlesThe magnet cannot separate iron and sulfur particles in a compoundcompound diagram

  • ReferencesSteve Lewis for the Royal Society of Chemistry

    Photographs by Peter Hollamby

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