AlkanesandAlkenes烷烃和烯烃.pptx

《AlkanesandAlkenes烷烃和烯烃.pptx》由会员分享，可在线阅读，更多相关《AlkanesandAlkenes烷烃和烯烃.pptx（45页珍藏版）》请在得力文库 - 分享文档赚钱的网站上搜索。

1、Alkanes and AlkenesAlkenesAlkanesSummary activitiesCombustion of alkanes ContentsCracking and polymerization 第1页/共45页Because the main use of hydrocarbons is as a fuel there is no point in going to the effort to separate them into individual hydrocarbons.It is,however,possible to obtain pure hydrocar

2、bons by very careful distillation.This section is about pure hydrocarbons.Pure hydrocarbons第2页/共45页Carbon is an unusual atom in that it is able to form very strong covalent bonds with other carbon atoms.When we then include its ability to also bond with other elements we open up the possibility of t

3、he highly diverse and complex molecules(like DNA)that have led to the possibility of life.Because of this,the chemistry of carbon containing compounds is often called organic chemistry.organic chemistry.Organic chemistry:carbon第3页/共45页The simplest hydrocarbons form a series of compounds known as alk

4、anes.These all consist of carbon and hydrogen only and every carbon has four single covalent bonds.HydrocarbonFormulaStructureMethaneCH4Ethane C2H6PropaneC3H8ButaneC4H10hydrogencarbon Alkanes第4页/共45页The names of the 4 simplest alkanes are methane,ethane,propane and butane.After that the names are sy

5、stematic(like the words used to describe geometric shapes).E.g.5 carbons=pentane C5H126 carbons=hexaneC6H147 carbons=heptane C7H168 carbons=octaneC8H189 carbons=nonaneC9H2010 carbons=decane C10H22carbonhydrogenpentane Names of alkanes第5页/共45页Alkanes all have very similar structures.They all consist

6、of carbon and hydrogen only and every carbon has four single covalent bonds.They have a CH3 at each end of the molecule.What differs is the number of CH2 groups between the two ends.It is possible to build up a series by simply adding an extra CH2 groupThis leads to a general formula of CnH2n+2hydro

7、gencarbonn=1 n=2 n=3 n=4 Structure of alkanes第6页/共45页What will be the formula for alkanes containing the following numbers of carbons?C12H26C16H34C31H64C19H40Number of carbonsFormula1216 3119 Whats the formula?第7页/共45页Although normal chemical formula-like C5H12-are used to describe alkanes,they do n

8、ot convey which atom is joined to which other atom.To get around this we often used displayed formulae to describe organic molecules.Displayed formulae show which 4 atoms each carbon is bonded to,but even these do not show the actual 3D shapes.For that we use models.methane,CH4CHHHH Formulae and mod

9、els of alkanes第8页/共45页CHHHHmethane,CH4CHHHCHHHethane,C2H6CHHHCHHCHHHpropane,C3H8 Formulae and models of alkanes第9页/共45页butane,C4H10CHHHCHHCHHCHHHpentane,C5H12CHHHCHHCHHCHHCHHH Formulae and models of alkanes第10页/共45页CHHHCHHCHHCHHCHHCHHHhexane,C6H14and so onNotice the carbon chainis not really straigh

10、t Formulae and models of alkanes第11页/共45页Alkanes of the same formula can have different arrangements of atoms.Such different arrangements are known as isomers.isomers.Two isomers of C4H10 are shown:Isomers of butane Isomerism第12页/共45页CHHHHCHHHHAlkanes contain atoms held together by single covalent b

11、onds.In the displayed formula we show these bonds as a single line.Each line is really a pair of shared electrons.Bonding in alkanes:methane第13页/共45页Ethane is the simplest alkane containing a C-C single covalent bond.CHHHCHHHCHHCHHHH Bonding in alkanes:ethane第14页/共45页Complete the diagram below inclu

12、ding its electrons.CHHCHHHHCHHCarbon electronHydrogen electron Bonding in alkanes:propane第15页/共45页Alkanes and AlkenesAlkenesAlkanesSummary activitiesCombustion of alkanesCracking and polymerization Contents第16页/共45页Alkanes are not especially reactive but they do undergo one very important reaction:c

13、ombustion.With an adequate supply of air they react to form carbon dioxide and water.methane+oxygen water +carbon dioxideCH4 +2O2 2H2O +CO2 Combustion of alkanes第17页/共45页In the absence of an adequate supply of air,alkanes may react to form carbon monoxide and water.Carbon monoxide is highly poisonou

14、s and this is one reason why gas boilers must be serviced regularly.methane+oxygen water +carbon monoxide2CH4 +3O2 4H2O +2COA carbon monoxide detector Incomplete combustion of alkanes第18页/共45页Complete the equations below assuming an adequate supply of oxygen for complete combustion.(These are quite

15、tricky!)1.2C2H6 +7O2 2.C3H8 +5O2 3.2C4H10 +13O2 1.2C2H6 +7O2 4CO2 +6H2O2.C3H8 +5O2 3CO2 +4H2O3.2C4H10 +13O2 8CO2 +10H2O Complete the equation第19页/共45页Alkanes and AlkenesAlkenesAlkanesSummary activitiesCombustion of alkanesCracking and polymerization Contents第20页/共45页When carbon forms compounds each

16、carbon atom always forms four bonds.This does not,however,mean that each carbon is joined to four other atoms.It is possible to have bonds grouped into pairs.These are called double bonds.Alkenes contain carbon atoms joined by double covalent bonds.Single covalent bondCCDouble covalent bondCC Alkene

17、s第21页/共45页A series of alkanes exist,differing only in the number of CH2 groups.The same is true for alkenes.This leads to a homologous series with the general formula CnH2n.hydrogencarbonn=1 n=2 n=3 n=4Alkenesnone=Structure of alkenes第22页/共45页What will be the formula for alkenes containing the follo

18、wing numbers of carbons?Number of carbonsFormula1113 3221C11H22C13H26C32H64C21H42 Whats the formula?第23页/共45页The simplest alkene is ethene.It has the formula C2H4The carbon atoms are joined together by a double bond.Its displayed formula may be drawn in slightly different forms but should always cle

19、arly show the double bond.CHHCHHor The formula of ethene第24页/共45页In all alkenes there are two carbon atoms that are joined by twotwo pairs of electrons.This is the double bond.CHHCHH The electron structure of ethene第25页/共45页Displayed formula for propene and butene are shown.Draw a displayed structur

20、e for pentene.CCCHHHHHHCCHHHCCHHHHHCCHHHCCHHHHHHHC The structure of pentene第26页/共45页Saturated means“full up”.They have a double bond that could instead become two single bonds.This means that other atoms can be added.It is not“full up”.Alkenes are unsaturatedunsaturated.Every carbon atom has already

21、 used all four of its bonds to join to four other atoms.No other atoms can be added.Alkanes are saturatedsaturated.Saturated or unsaturated?第27页/共45页Alkenes are unsaturated and so extra atoms can be added to alkene molecules.This forms the basis of a test to distinguish between alkanes and alkenes.W

22、hen bromine water is added to an alkane nothing happens,but when bromine is added to an alkene the red colour of the bromine disappears.+Br2 gas red colourlessBromine loses this red colour Testing for alkanes and alkenes第28页/共45页Copy the table and complete the empty boxes.Number of carbonsNameAlkane

23、 or alkeneFormula5pentene8octane4butene10decanealkeneC5H10alkaneC8H18alkeneC4H8alkaneC10H22 Identify the compound第29页/共45页Alkanes and AlkenesAlkenesCracking and polymerization AlkanesSummary activitiesCombustion of alkanes Contents第30页/共45页Crude oil contains many large molecules.If these are to be u

24、sed as fuels or feedstock for the chemical industry then they have to be broken down(or cracked)into smaller molecules.Big moleculesSmall moleculesMedium molecules Source of alkenes第31页/共45页Large hydrocarbons are broken down into smaller molecules using heat and a catalyst.This process is known as c

25、atalytic cracking.The small molecules produced are then separated by distillation.CatalyticcrackerHeat tovaporizeDistillationtowerpressureBig moleculesSmaller moleculesMolecules break up Catalytic cracking第32页/共45页In the catalytic cracker long chain molecules are split apart or cracked.An example of

26、 such a reaction is:C8H18 C6H14+C2H4+etheneoctanehexaneUsedto makeplasticsheat&pressurecatalystUsed as a fuel Catalytic cracking第33页/共45页Draw out displayed formulae of a pair of products formed by cracking decane.Heat&pressurecatalystHHCCHHHHHCCHHHHCCHHHHCCHHHHCCHHHdecane Cracking decane+etheneHHCCH

27、HHHHCCHHHHCCHHHCHHCHHoctane第34页/共45页 Making polymersHow do monomers become polymers?第35页/共45页One important reaction of alkenes involves the joining together of alkene molecules.HHCCHHHHHCCHHHHCCHHHHCCHHHHCCHHAndlotsmore.This is called addition polymerizationaddition polymerization and is written as:

28、pressurehigh temperaturecatalystnnethenepoly(e)thene1 2 3 4 5 thousands Production of polythene第36页/共45页Ethene is only one alkene.Other unsaturated molecules such as propene,vinyl chloride and styrene can also be polymerizedpolymerized to produce a range of plastics.E.g.propene:poly(propene)nnpropen

29、e Polypropene第37页/共45页Tetrafluoroethene is another alkene that is made into an important plastic used to coat non-stick pans:polytetrafluoroethene or PTFE.ntetrafluoroethenepoly(tetrafluoroethene)or PTFEn PTFE第38页/共45页pvcCCHHHClnnVinyl chlorideC CClHHHFill in the products that will be obtained from

30、vinyl chloride Polymerization of vinyl chloride第39页/共45页Poly(e)theneShopping bagsBottlesBucketsWashing-up bowlsPolypropeneMilk cratesRopeCarpet fibresPolystyrenePackingInsulationBall pens Uses of plastics第40页/共45页Alkanes and AlkenesAlkenesAlkanesSummary activitiesCombustion of alkanesCracking and po

31、lymerization Contents第41页/共45页 Glossarylalkanes A family of saturated hydrocarbons used as fuels.lalkenes A family of unsaturated hydrocarbons containing one double bond,and which are used to make plastics.lcracking The process in which large molecules are broken down into smaller molecules by heati

32、ng.lmonomer A molecule that joins with others to form a polymer.lpolymerization The process in which small molecules are joined together to form a much larger molecule.lsaturated A molecule in which all the bonds are single.lunsaturated A molecule in which at least one bond is double or triple.第42页/共45页 Anagrams第43页/共45页 Multiple-choice quiz第44页/共45页感谢您的观看！第45页/共45页