HYDROCARBONS
Hydrocarbons
Compounds that contain only carbon
atoms and hydrogen atoms.
Obtained from crude oil by fractional
distillation and can be classified into
different groups.
There are different types of hydrocarbons.
Each type is known as a homologous
series.
Members of each series share similar
structures and properties.
Homologous series – Alkanes (single
covalent bonds)
Homologous series - Alkenes (contain one
C=C double covalent bond)
Properties of Alkanes
Alkanes are called saturated
hydrocarbons because they only have
single bonds between the carbon atoms.
C2 H6
(graphical formula)
Molecular formula
The name of the alkane depends upon
how many carbon atoms the chain has.
1C
methane
2C
ethane
3C
propane
4C
butane
The chain may have a branch. The name
of the alkane will indicate this.
2-methyl propane
Properties of Alkanes
 The general formula for an alkane is:
CnH2n+2
 As the number of carbon atoms in a chain
increases, bpt and viscosity increases. This is
because the molecules are attracted to each
other and as chain length increases so does the
attraction (more energy needed to separate
them). (Flammability decreases).
Properties of Alkanes
Alkanes burn in a plentiful supply of air to
release energy (this is why they are used
as fuels).
Burning (properly called combustion) also
produces carbon dioxide and water
vapour.
COMPLETE COMBUSTION of methane
CH4 (g) + O2 (g) → CO2 (g) + H2O (g)
Can you balance the equation???
Blue flame (COMPLETE COMBUSTION)
If the oxygen supply is restricted then the
combustion of alkanes produces the
poisonous gas carbon monoxide and
carbon (soot – responsible for the
blackening of buildings).
INCOMPLETE COMBUSTION of methane
CH4 (g) + O2 (g) → CO (g) + H2O (g)
Can you balance the equation???
Orange flame (INCOMPLETE
COMBUSTION)
Alkenes
Alkenes are also hydrocarbons but they
contain a double bond between two of the
carbon atoms.
Alkenes are said to be unsaturated
because of the double bond
General formula: CnH2n
Properties of alkenes
 Bpt increases with chain length.
 Alkenes undergo combustion (burning) in a similar way
to alkanes.
 The double bond makes them more reactive than
alkanes, therefore undergo more chemical reactions
 Bromine can be added to the double bond. This is called
an addition reaction. The reaction makes the red colour
of 'bromine solution' disappear. (This reaction is used to
test for a double bond a.k.a unsaturated molecule).
Testing for unsaturation
(g)
+
Ethene (colourless)
Br2
(l)
(aq)
(orange)
(colourless)
http://www.youtube.com/watch?v=2C_6ax
2TsV8
Questions to do:
Pg 175-177 Q3, 7, 13
Pg 256 Q21, 22