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Unit 2 Summery Nature’s Chemistry

Unit 2 Summery Nature’s Chemistry. National 5 Supported Study. Mandatory Key Area. Homologous series The study of cycloalkanes and branched chain alkanes and alkenes (up to C8).

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Unit 2 Summery Nature’s Chemistry

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  1. Unit 2 Summery Nature’s Chemistry National 5 Supported Study

  2. Mandatory Key Area Homologous series • The study of cycloalkanes and branched chain alkanes and alkenes (up to C8). • To include their physical, chemical properties, general formulae, systematic names, structural formulae, uses, reactions and isomers. • Reactions — combustion and addition.

  3. Key Definitions • Homologous Series – family of compounds with same general formula and similar chemical properties • Isomers - Have the same molecular formula but a different structural formula. • Butene and cyclobutane are isomers

  4. Family 1 : Alkanes • Alkanes • Are straight chained hydrocarbons • All end in –ane

  5. Naming Alkanes (pg 9 DB) • Methane - 1 carbon • Ethane - 2 carbons • Propane - 3 carbons • Butane - 4 carbons • Pentane - 5 carbons • Hexane - 6 carbons • Heptane - 7 carbons • Octane - 8 carbons All Alkanes end in –ane

  6. Monkey's Eat Peanut Butter • Meth • Eth • Prop • But

  7. General Formula

  8. Alkanes

  9. Family 2: Alkenes • Are straight chain hydrocarbons • End in – ene • Contain a carbon to carbon DOUBLE bond • General Formula • CnH2n

  10. Naming Alkenes • Ethene - 2 carbons • Propene - 3 carbons • Butene - 4 carbons • Pentene - 5 carbons • Hexene - 6 carbons • Heptene - 7 carbons • Octene - 8 carbons All Alkenes end in –ene Why does Methene not exist????

  11. Alkenes

  12. Saturated Vs Unsaturated • Saturated = single carbon to carbon bonds only • Unsaturated = contains carbon to carbon double bonds. Remember • Keep the S’s together (saturated/single) • Keep the U’s together (Unsaturated/Double)

  13. Bromine Water • Bromine water is used to distinguish between saturated and unsaturated compounds. Alkenes decolourises bromine water.

  14. Family 3: Cycloalkanes • Ring structure • Saturated • Cyclopropane first Member of series • General Formula CnH2n (same as alkenes)

  15. Systematic Naming • Find the longest chain (numbering carbons helps) • Always give functional group lowest numbers • “,” between numbers and “–” between numbers and words PRACTICE PRACTICE PRACTICE

  16. Systematic Naming • Branched chain alkanes • Branched chain alkenes

  17. Branched Chain Alkanes • Find the longest chain • Note – it might not always be the most obvious one, Could be going up and down a page, or have a bend it. You are looking for the longest path.

  18. Don’t be tricked!! Longest chain is still 5 carbons

  19. Number the carbons to give the branch the lowest number possible As alkanes do not have a functional group the carbons are numbered to give the branch the lowest numbers possible.

  20. By numbering your carbons in the main straight chain, it makes it easier to identify the branch and which carbon it is attached too. Branch attached to carbon 2

  21. Different Branches • Methyl --- CH3 • Ethyl -----C2H5

  22. Systematic Naming • 2-methylbutane

  23. 3,3-dimethylhexane • Di = 2 methyl groups • , = used between numbers • 3,3= the carbons which the methyl branches can be located

  24. Systematically Naming Alkenes • Same rules as alkanes • Functional group the (C=C) gets first priority when numbering the carbons. • C=C gets lowest numbers before branches

  25. Position of C=C • The position of the C=C must be stated. hex-1-ene • The one tells us that the C=C comes after carbon 1

  26. 5-methyl hex-1-ene

  27. Uses/Properties of Alkanes Physical Properties in BRANCHED ALKANES • Have higher Bp’s • Higher Volatility (evaporate easier) • (Compared with straight chain alkanes) Uses of Branched Alkanes • Petrol manufacture. Used to improve how smoothly a fuel burns. Branched alkanes burn more smoothly than straight chain alkanes • For a fuel to burn it must vaporise and mix with air so volatility important too. In winter more volatile compounds are added to ensure the petrol vaporises easier.

  28. Uses of Cycloalkanes • Have higher mp’s and bp’s compared to alkanes Uses • Used in petrol (like branches alkanes) as burn more smoothly than alkanes • Solvents for paints and varnishes

  29. Isomers • Branched chain alkanes • Alkenes • Cycloalkanes

  30. Drawing Isomers - Alkanes • Must always be an alkane • Can’t draw alkenes, or cycloalkanes • Make a branch • Must not be on the first or last carbon • If it has a branch – draw a straight chain alkane • Write the molecular formula • Does it have the same number of carbon and hydrogen • Systematically name the structure • This is a good way to check you have not just drawn the same structure twice

  31. Drawing Isomers - Alkenes • Move the position of the double bond • Remember the double bond always gets given the lowest number so can only do this once or twice • Need to have at least 4 carbons before can move the C=C

  32. Drawing Isomers - Alkenes • Add a branch • Remember can’t be on first or last carbon • Watch out for the carbons round the double bonds. • Remember carbon only makes 4 bonds • Draw a cycloalkane • Alkenes and cycloalkanes have the same general formula so they are isomers of each other.

  33. Are these Isomers?? • Check the molecular formulas • Do they have the same number of carbons and hydrogens • Is the structure different • This can be easily checked by systematically naming the compounds.

  34. suction pump burning gas limewater ice water Reactions • Combustion ( Reacting with oxygen) Combustion of any Hydrocarbon produces CO2 and H2O Colourless liquid goes cloudy.

  35. Addition Reactions • Involves the breaking of a carbon to carbon double bond. • Small molecule added across double bond. • E.g. H2O, H2, Br2. HBr

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