Alkanes
Alkanes
 Contain
C and H only
 Contain
single bonds C-C
 Have
 Are
4 bonds to every carbon (C) atom
nonpolar
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Complete Structural Formulas
Show the bonds between each of the
atoms
H
H

HCH
H
C
H

H
H
CH4 , methane
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More Alkanes
H
H
H
H
C
C
H
H
Condensed Structural Formulas
H
CH3
CH3
Ethane
H
H
H
C
C
C
H
H
H
H
CH3 CH2 CH3
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Propane
4
IUPAC Names
Name
# carbons
Structural Formula
Methane 1
CH4
Ethane
CH3CH3
2
Propane 3
CH3CH2CH3
Butane
CH3CH2CH2CH3
4
Pentane 5
CH3CH2CH2CH2CH3
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IUPAC NAMES
Name # carbons
Structural Formula
Hexane 6
CH3CH2CH2CH2CH2CH3
Heptane 7
CH3CH2CH2CH2CH2CH2CH3
Octane
8
CH3CH2CH2CH2CH2CH2CH2CH3
Nonane 9
CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
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Alkanes
Alkanes are a family of hydrocarbons
containing only single bonds between
the carbon atoms
Methane
Tetrahedral
Expanded structural formula:
showing each bond line.
Molecular formula CH4
Ethane
C2H6
Molecular formula
Expanded structural
formula
CH3 – CH3
Condensed structural formula: with each carbon atom and
its attached hydrogen atoms.
Alkanes
Homologous Series general formulaCnH2n+2
n: number of carbon atoms
Naming of Alkanes
Prefix + ane
CnH2n+2
No of C atoms
1
2
3
4
5
6
7
8
9
10
Prefix
methethpropbutpenthexheptoctnondec-
• Carbon-to-carbon chains can
be (A) straight, (B) branched,
or (C) in a closed ring.
• (Some carbon bonds are
drawn longer, but are actually
the same length.)
Review
• Work through the Sample Problem page
175
• Complete the revision questions page
175 (1 – 3)
Learning Check Alk1
A. What is the condensed formula for
H H H H
H
C
C
C
C
H
H
H H
H
B. What is its molecular formula?
C. What is its name?
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Solution Alk1
A.
CH3CH2CH2CH3
B.
C4H10
C.
butane
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Reactions of Alkanes
• Alkanes burn in oxygen to form carbon
dioxide and water - oxidation or
combustion reaction
• CH4(g) + O2(g)
CO2(g) + 2H2O(g)
• Alkanes react with chlorine or fluorine in a
reaction called a substitution reaction
(one of the chlorine or fluorine atoms
takes the place of one or more of the
hydrogen atoms
17
Reactions of Alkanes
Combustion
alkane + O2
CO2 + H2O + heat
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Combustion In the Cell
Metabolic oxidation is combustion
C6H12 O6 + 6O2
6CO2 + 6H2O + heat
glucose
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Learning Check Alk2
Complete the combustion reaction for
C 3H 8 + O 2
+
Balance your equation
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Solution Alk2
Step 1
C 3H 8 + O 2
CO2 + H2O
Step 2
C 3H 8 + O 2
3 CO2 + 4 H2O
Step 3
C 3H 8 + 5 O 2
3 CO2 + 4 H2O
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Learning Check Alk3
Complete and balance the reaction for
the complete combustion of C7H16
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Solution Alk3
Step 1
C7H16 + O2
CO2 + H2O
Step 2
C7H16 + O2
7 CO2 + 8 H2O
Step 3
C7H16 + 11 O2
7 CO2 + 8 H2O
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Review
• Complete the revision questions page
175 (4 - 6)
Isomers
• Straight chain alkanes: An alkane
that has all its carbons connected in a
row.
• Branched chain alkanes: An alkane
that has a branching connection of
carbons.
• Isomers: Compounds with same
molecular formula but different
structures.
• There is only one possible way that the
carbons in methane (CH4), ethane (C2H6),
and propane (C3H8) can be arranged.
• However, carbons in butane (C4H10) can
be arranged in two ways; four carbons in a
row (linear alkane) or a branching
(branched alkane). These two structures
are two isomers for butane.
Butane
29
Different isomers are
compounds.
They have
different physical properties
and boiling point, and
physiological properties.
completely different
different structures,
such as melting point
may have different
Review
• Complete revision questions page 176
(7 – 9)
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