4.5 ALKANES AND ALKENES Flashcards
general formula of alkanes:
CnH2n+2
names of the first five alkanes:
- methane CH4
- ethane C2H6
- propane C3H8
- butane C4H10
- pentane C5H12
displayed formula:
drawn out showing the positions of every atom and every bond
structural formula (butane example):
shows the structure of the molecule in one line
CH3CH2CH2CH3
molecular formula (butane example):
shows only how many hydrogen and carbon atoms there are
C4H10
empirical formula (butane example):
shows the simplest whole-number ratio of carbon to hydrogen
what is a homologous series?
- similar chemical reactions
- trends in physical properties (boiling points, viscosity, colour)
- same general formula
what is an isomer in alkanes?
molecules with the same molecular formula but a different structural formula
complete combustion:
- alkane + oxygen —> carbon dioxide + water
- occurs when there is excess oxygen
incomplete combustion:
- occurs when there isn’t enough oxygen
- produces carbon monoxide and soot
- releases less energy
what does the combustion of alkanes/alkenes as fuels produce?
- carbon dioxide (greenhouse gas)
- nitrogen oxide- forms when nitrogen in the air combusts (acid rain)
- sulphur dioxide- forms when sulphur impurities in the fuel combusts (acid rain)
how do alkanes react with halogens?
by swapping one hydrogen atom for one halogen atom
details for alkanes reacting with halogens:
- substitution reaction because the H swaps with the Br
- requires UV light because the alkane is unreactive
are alkanes and alkenes hydrocarbons?
yes
general formula for alkenes:
CnH2n
first four alkenes:
- ethene C2H4
- propene C3H6
- butene C4H8
- pentene C5H10
difference between alkanes and alkenes:
- alkenes have one C=C double bond in their carbon chain
- in the structural formula this is sometimes shown as “=”
what are alkenes?
- homologous series of organic molecules
- family of molecules which have:
1. similar chemical reactions
2. trends in physical properties (colour, boiling points, viscosity)
3. same general formula
do alkenes have isomers?
- yes
- they can differ in more than one way (unlike alkanes)
how can alkenes differ in two ways in isomers?
- branch off of the carbon chain
- the position of the C=C bond
are alkenes saturated or unsaturated?
- unsaturated
- due to their C=C bond
are alkanes saturated or unsaturated?
- saturated
- because their is no C=C bond
how do alkenes react with bromine?
- break the C=C bonds and add bromine
details for alkenes reacting with bromine:
- addition reaction- adding bromine atoms to alkene
- happens without UV light because alkenes are more reactive than alkanes
- works with pure bromine liquid or bromine water (which is orange)
- mixture turns orange to colourless because the bromine is used up during the reaction
