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Alkanes, Alkenes and Polymers CHEMISTRY 2 GCSE Additional ScienceChapter 9.

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Presentation on theme: "Alkanes, Alkenes and Polymers CHEMISTRY 2 GCSE Additional ScienceChapter 9."— Presentation transcript:

1 Alkanes, Alkenes and Polymers CHEMISTRY 2 GCSE Additional ScienceChapter 9

2 Hydrocarbons The alkanes are hydrocarbons (they contain carbon and hydrogen only).… they are represented by the formula C n H (2n+2) where n = 1,2,3,4 etc. CRUDE OIL Fractional distillation in an oil refinery ALKANES C H H H HC H H H C H H H C H H H C H H C H H H C H H H C H H C H H C H H H H C H H H C H H C H H C H H C H H Methane CH 4 Ethane C 2 H 6 Propane C 3 H 8 Butane C 4 H 10 Pentane C 5 H 12 The lines represent covalent bonds where electrons are shared saturated hydrocarbons There are only single bonds between the carbon atoms in alkanes so they are called saturated hydrocarbons. Apart from burning, they are unreactive. GCSE Additional ScienceChapter 9

3 Cracking Cracking Cracking is the term used when a saturated hydrocarbon molecule is heated in the presence of a catalyst in order to break it down into smaller units – smaller alkanes (which burn better) and alkenes (which can be used to make other chemicals, such as polymers). H C H H H C H H C H H C H H C H H C H H C H H C H H C H H C H H Decane C 10 H 22 Cracking H C H H H C H H C H H C H H C H H C H H C H H C H H Octane C 8 H 18 C H H H H C + Ethene C 2 H 4 Notice the double bond. This makes ethene reactive, and it is described as an unsaturated hydrocarbon. Ethene can be used to make poly (ethene) or polythene. GCSE Additional ScienceChapter 9

4 Making Polymers The name of the small molecule used to make a polymer is a monomer. The monomer ethene forms an addition polymer (a polymer made up of similar monomers) called polythene [poly(ethene)] C H H H H C Ethene C 2 H 4 Poly(ethene) (C 2 H 4 ) n Note that one of the bonds in the double bond has broken allowing the ethene molecule to join the others to form the polymer. GCSE Additional ScienceChapter 9 C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H C H H

5 Polymers we use often Poly(tetrafluoroethene) C F F F F C Monomer tetrafluoroethene C 2 F 4 Poly(tetrafluoroethene) PTFE (C 2 F 4 ) n PTFE is inflammable and it’s used as a non-stick coating for saucepans and frying pans. Poly(chloroethene) H H C H Cl C Monomer chloroethene C 2 H 3 Cl Poly(chloroethene) PVC (C 2 H 3 Cl) n PVC is strong and light. It’s used for buckets, window frames and doors. GCSE Additional ScienceChapter 9 C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C F F C H H C H Cl C H H C H C H H C H C H H C H C H H C H C H H C H C H H C H C H H C H C H H C H C H H C H

6 Thermoplastics and thermosets Thermoplastics Thermoplastics is the name given to plastics that melt when heated. They are used to make bowls, buckets and clingfilm. Thermosets Thermosets is the name given to plastics that do not soften when heated. They are used to make saucepan handles and electrical fittings. The difference:- ThermoplasticsThermosets Thermoplastics are long chains with weak bonds between them. These chains slip easily over each other, which explains why they melt when heated gently. The chains are connected by cross-links within a thermoset. A lot of heat energy is needed to break these cross-links, so they do not soften (melt) when heated. GCSE Additional ScienceChapter 9

7 Advantages and Disadvantages of Polymers Polymers Advantages Disadvantages Cheap Water doesn’t affect them Strong for their weight Easy to mould into different shapes Light Suitable for a wide variety of uses Do not corrode Made from a non-renewable resource Traps and kills Animals when it’s litter Many are non-biodegradable Creates rubbish and pollution Must recycle them to maintain clean environment Use less energy to make than traditional materials GCSE Additional ScienceChapter 9


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