Hydrocarbons
• A hydrocarbon is a compound
containing the elements H and C
only.
• A Homologous Series is a group
of Hydrocarbons with the same
General Formula and similar
Chemical Properties.
The Alkanes
• Simplest group of Hydrocarbons.
• General formula – CnH2n+2( n=
number of Carbon atoms)
• Mainly used as fuels.
• Have only Carbon to Carbon
single bonds in their structure.
• This makes them SATURATED.
Alkanes – more info!
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Name
Methane
Ethane
Propane
Butane
Pentane
Hexane
Heptane
Octane
Molecular Formula
CH4
C2H6
C3H8
C4H10
C5H12
C6H14
C7H16
C8H18
Alkane - Structure
Alkenes
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General Formula CnH2n
Contain C=C double bonds.
They are Unsaturated.
Again can be used as fuels.
Test – decolourise Bromine
water – INSTANTLY!
• Colour change Brown - Clear
The Names!
• Alkene
Ethene
Propene
Butene
Pentene
Hexene
Heptene
Octene
Molecular formula
C2H4
C3H6
C4H8
C5H10
C6H12
C7H14
C8H16
Alkene - Structure
Cycloalkanes
• General formula CnH2n
• They are saturated – no double
bonds.
• They have a ring in their
structure.
• They are isomers with alkenes.
Cycloalkane - names
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Name
Molecular Formula
Cyclopropane C3H6
Cyclobutane C4H8
Cyclopentane C5H10
Cyclohexane C6H12
Cycloheptane C7H14
Cyclooctane C8H16
Cycloalkane - Structure
Cracking!
• There are more of the heavier
less useful fractions.
• We can “chop” them up into
smaller – more useful ones.
• This is called “Cracking”
• We need heat and a catalyst for
this!
Products of Cracking
• An Unsaturated product
(contains double bond) and a
Saturated product ( single bonds
only) are always formed.
• Example
• C12H26 —>C4H8 + C6H14
+C2H4
Isomers
• Isomers are compounds with the same
molecular formula but a different structural
formula.
• Example
• C4H10 – this has 2 isomers.
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H H H H
H CH3 H
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I I
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• H - C – C – C – C – H and H - C – C – C - H
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H H
H
H
H
H H
More Isomers
• The alkenes and cyclo alkanes
are isomers.
• Example
• C3H6 is the molecular formula
for both propene and cyclo
propane.
• They both have different
structures.