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Click to edit Master title style,Boardworks Ltd 2005,*,of 45,KS4 Chemistry,Alkanes and Alkenes,KS4 Chemistry Alkanes and Alke,Alkanes and Alkenes,Alkenes,Alkanes,Summary activities,Combustion of alkanes,Contents,Cracking and polymerization,Alkanes and AlkenesAlkenesAlka,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 hydrocarbons by very careful distillation.,This section is about pure hydrocarbons.,Pure hydrocarbons,Because the main use of hydroc,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 the 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:carbon,Carbon is an unusual atom in t,The simplest hydrocarbons form a series of compounds known as alkanes.,These all consist of carbon and hydrogen only and every carbon has four single covalent bonds.,Hydrocarbon,Formula,Structure,Methane,CH,4,Ethane,C,2,H,6,Propane,C,3,H,8,Butane,C,4,H,10,hydrogen,carbon,Alkanes,The simplest hydrocarbons form,The names of the 4 simplest alkanes are methane,ethane,propane and butane.,After that the names are systematic(like the words used to describe geometric shapes).E.g.,5 carbons=pentane,C,5,H,12,6 carbons=hexane,C,6,H,14,7 carbons=heptane,C,7,H,16,8 carbons=octane,C,8,H,18,9 carbons=nonane,C,9,H,20,10 carbons=decane,C,10,H,22,carbon,hydrogen,pentane,Names of alkanes,The names of the 4 simplest al,Alkanes all have very similar structures.,They all consist of carbon and hydrogen only and every carbon has four single covalent bonds.,They have a CH,3,at each end of the molecule.,What differs is the number of CH,2,groups between the two ends.,It is possible to build up a series by simply adding an extra CH,2,group,This leads to a general formula of,C,n,H,2n+2,hydrogen,carbon,n=1 n=2 n=3 n=4,Structure of alkanes,Alkanes all have very similar,What will be the formula for alkanes containing the following numbers of carbons?,C,12,H,26,C,16,H,34,C,31,H,64,C,19,H,40,Number of carbons,Formula,12,16,31,19,Whats the formula?,What will be the formula for a,Although normal chemical formula-like,C,5,H,12,-,are used to describe alkanes,they do not 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,CH,4,C,H,H,H,H,Formulae and models of alkanes,Although normal chemical formu,C,H,H,H,H,methane,CH,4,C,H,H,H,C,H,H,H,ethane,C,2,H,6,C,H,H,H,C,H,H,C,H,H,H,propane,C,3,H,8,Formulae and models of alkanes,CHHHHmethane,CH4CHHHCHHHetha,butane,C,4,H,10,C,H,H,H,C,H,H,C,H,H,C,H,H,H,pentane,C,5,H,12,C,H,H,H,C,H,H,C,H,H,C,H,H,C,H,H,H,Formulae and models of alkanes,butane,C4H10CHHHCHHCHHCHHHpen,C,H,H,H,C,H,H,C,H,H,C,H,H,C,H,H,C,H,H,H,hexane,C,6,H,14,and so on,Notice,the carbon chain,is not really,straight,Formulae and models of alkanes,CHHHCHHCHHCHHCHHCHHHhexane,C6,Alkanes of the same formula can have different arrangements of atoms.Such different arrangements are known as,isomers.,Two isomers of C,4,H,10,are shown:,Isomers of butane,Isomerism,Alkanes of the same formula ca,C,H,H,H,H,C,H,H,H,H,Alkanes contain atoms held together by single covalent bonds.,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,CHHHHCHHHHAlkanes contain atom,Ethane is the simplest alkane containing a C-C single covalent bond.,C,H,H,H,C,H,H,H,C,H,H,C,H,H,H,H,Bonding in alkanes:ethane,Ethane is the simplest alkane,Complete the diagram below including its electrons.,C,H,H,C,H,H,H,H,C,H,H,Carbon electron,Hydrogen electron,Bonding in alkanes:propane,Complete the diagram below inc,Alkanes and Alkenes,Alkenes,Alkanes,Summary activities,Combustion of alkanes,Cracking and polymerization,Contents,Alkanes and AlkenesAlkenesAlka,Alkanes are not especially reactive but they do undergo one very important reaction:combustion.,With an adequate supply of air they react to form carbon dioxide and water.,methane+oxygen,water +carbon dioxide,CH,4,+2O,2,2H,2,O +CO,2,Combustion of alkanes,Alkanes are not especially rea,In the absence of an adequate supply of air,alkanes may react to form carbon monoxide and water.,Carbon monoxide is highly poisonous and this is one reason why gas boilers must be serviced regularly.,methane+oxygen,water +carbon monoxide,2CH,4,+3O,2,4H,2,O +2CO,A carbon monoxide detector,Incomplete combustion of alkanes,In the absence of an adequate,Complete the equations below assuming an adequate supply of oxygen for complete combustion.,(These are quite trick
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