Alkanes and Alkenes:烷烃和烯烃.ppt
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1、KS4 Chemistry,Alkanes and Alkenes,Alkanes and Alkenes,Alkenes,Alkanes,Summary activities,Combustion of alkanes,Contents,Cracking and polymerization,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
2、, possible to obtain pure hydrocarbons by very careful distillation. This section is about pure hydrocarbons.,Pure hydrocarbons,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 w
3、e 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,The simplest hydrocarbons form a series of compounds k
4、nown as alkanes. These all consist of carbon and hydrogen only and every carbon has four single covalent bonds.,hydrogen,carbon,Alkanes,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).
5、 E.g. 5 carbons = pentane C5H12 6 carbons = hexane C6H14 7 carbons = heptane C7H16 8 carbons = octane C8H18 9 carbons = nonane C9H20 10 carbons = decane C10H22,pentane,Names of alkanes,Alkanes all have very similar structures. They all consist of carbon and hydrogen only and every carbon has four si
6、ngle 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 group This leads to a general formula of CnH2n+2,Structure of alkanes,What will be the formula for alkane
7、s containing the following numbers of carbons?,C12H26,C16H34,C31H64,C19H40,Whats the formula?,Although normal chemical formula - like C5H12 - 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 org
8、anic 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, CH4,Formulae and models of alkanes,Formulae and models of alkanes,Formulae and models of alkanes,and so on,Notice the carbon chain is not
9、really straight,Formulae and models of alkanes,Alkanes of the same formula can have different arrangements of atoms. Such different arrangements are known as isomers. Two isomers of C4H10 are shown:,Isomers of butane,Isomerism,Alkanes contain atoms held together by single covalent bonds. In the disp
10、layed formula we show these bonds as a single line. Each line is really a pair of shared electrons.,Bonding in alkanes: methane,Ethane is the simplest alkane containing a C-C single covalent bond.,Bonding in alkanes: ethane,Complete the diagram below including its electrons.,Bonding in alkanes: prop
11、ane,Alkanes and Alkenes,Alkenes,Alkanes,Summary activities,Combustion of alkanes,Cracking and polymerization,Contents,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.,Combustio
12、n of alkanes,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.,A carbon monoxide detector,Incomplete combustion of alkanes,Complete the equations bel
13、ow assuming an adequate supply of oxygen for complete combustion. (These are quite tricky!),2C2H6 + 7O2 C3H8 + 5O2 2C4H10 + 13O2 ,2C2H6 + 7O2 4CO2 + 6H2O,C3H8 + 5O2 3CO2 + 4H2O,2C4H10 + 13O2 8CO2 + 10H2O,Complete the equation,Alkanes and Alkenes,Alkenes,Alkanes,Summary activities,Combustion of alkan
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