- Introduction
- Alkanes
Mr. Shields
Regents Chemistry
U16 L01
1
Organic Chemistry
• Organic Chemistry involves the study of Carbon
based compounds of which there are millions and
many more yet to be made
• Much more “diversity” than found in inorganic
compounds
• What are some examples of Carbon Based
compounds?
– Petrochemicals
– Dyes
– Pharmaceuticals
- Biochemicals
- Polymers
- Life
2
Source
• The source of almost all organic compounds
today is petroleum
– Crude oil
• Through Synthesis hydrocarbons can be further
modified into other organic compounds
• Petroleum (crude oil) is first separted into
several different categories at refineries
• Separation at refineries is a distillation process
based on BP (mol. Wt.)
3
Why so many C compounds?
• Carbon atoms can bond with other carbon
atoms in chains. These bonds are
Covalent.
• Since Carbon has 4 unpaired electrons it
can form 4 covalent bonds.
•
•C•
•
4
Formation of Carbons 4 covalent bonds
Carbons ability to form 4 covalent bonds, even with itself,
leads to carbons ability to form millions of different
compounds, some simple some very complex.
5
Properties of Covalent Substances
Covalent compounds are Molecular Compounds
• What do we mean by “Molecular” and What kind of properties do
they have?
 Low melting points & boiling points
 Poor conductors of heat & electricity
 Solids tend to be soft
 Can not be worked (not malleable)
 May be Polar or nonpolar
 Non-polar is not soluable in water
 Polar may be slightly sol. to sol. in water
 Non-polar will dissolve in non-polar solvents
 React more slowly than ionic compounds
6
Structural Formulas
• Shows kind & number of atoms and how they
are bonded together.
• They are 2-D drawings of 3-D objects so
structural formulas aren’t totally realistic.
H
H–C–H
H
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Structural Formulas
• “–” A single line represents one pair of
electrons (a single bond).
• “=“ A double line represents two pairs of
electrons (a double bond).
• “” A triple line represents three pairs of
electrons (a triple bond).
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Condensed Structural Formulas
• These formulas show kind & number of atoms as
well as some information regarding what atoms are
joined to what atoms but not how.
• They don’t depict bonds
Examples: CH4, CH3OH, CH3Cl, CH2Cl2,
CH3CH2CH2CH3, CH3COOH
No information given on how
these oxygen are bonded to this carbon
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Molecular Formulas
• These formulas show kind & number of atoms but
not necessarily any other information
Condensed Structural formula
Examples: CH3OH, CH3CH2CH2CH3, CH3COOH
Molecular formula
Becomes: CH4O,
C4H10,
C2H4O2
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Molecular Shape
• When carbon is bonded to 4 other atoms carbon is at
the center of a tetrahedron and the 4 other atoms are
located at the corners.
• This is known
As a
Tetrahedron
If there are 3 C’s
Bonded to each other
Then there are 3 joined
tetrahedrons
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Vocabulary Interlude
• Hydrocarbons: organic compounds
containing only Carbon and Hydrogen.
– Straight chain: All “internal” C bonded to only 2
other C’s
• Ex:
c-c-c-c-c-c-c
– Branched: One or more int. C bonded to 3 or 4
other C’s
• Ex:
c-c-c-c-c-c-c-c
| |
c c
c
|
c-c-c
|
c
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Vocabulary
• Saturated: organic compounds containing
only single bonds (carbon bonded to 4 atoms)
• Unsaturated: organic compounds containing
one or more double or triple bonds.
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Vocabulary
• Homologous Series: a group of
compounds with related structures and
properties.
– Each member of the series differs from the one
before it by the same additional unit. (Ex. The
Alkanes; each differs by one -CH2 unit)
Ex: CH4 C2H6 C3H8
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Primary Categories of Hydrocarbons
• There are 3 major Hydrocarbon Categories
– These can be Straight Chain or Branched
• Alkanes (Single Bonds) [hydrogen = 2n +2]
– CH3CH2CH2CH3
• Alkenes (Double Bond) [H = 2n]
– CH3CH2CH=CH2
• Alkynes (Triple Bond) [H = 2n – 2]
– CH3CH2C
CH
Table Q in your Reference Tables is where you can
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Get this information!
Naming straight-chain Alkanes
• All alkane names have the suffix –ane.
• The prefix depends on the number of C’s.
Ex:
Methane
Ethane
1 Carbon
2 Carbon
What’s the Molecular formula of each?
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Prefix
Meth ane
Eth
Prop
But
Pent
Hex
Hept
Oct
Non
Dec
# of C atoms
1
2
3
4
5
6
7
8
9
10
(Check out Table P in your Reference Tables)
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Alkanes
• A Homologous series of
saturated hydrocarbons.
• Compounds with a
related structure differing
by the same repeating
unit (-CH2-)
- General formula is
CnH2n+2 (n= no. of carbon
atoms)
Problem: What’s the molecular
formula for the
alkane with 27 carbon
Formula
Name
CH4
Methane
C2H6
Ethane
C3H8
Propane
C4H10
Butane
C5H12
Pentane
C6H14
Hexane
C7H16
Heptane
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Problem: What is the structural formula for pentane?
C-C-C-C-C
(Shown w/o the
Hydrogens)
Problem: What is the name of the following
Hydrocarbon?
CH3-CH2-CH2
Hexane!
CH2-CH2-CH3
Is it a branched or straight chain hydrocarbon?
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Properties of Alkanes
• Physical Properties
Change systematically
with the number of C’s
• As the number of C’s
In a homologous
series increases, the
b.p. & m.p. increases.
Mol.
M.P.
Formula
CH4
-182
C2H6
-183
C3H8
C4H10
C5H12
C6H14
C7H16
(Due to increasing Intermolecular force C H
8 18
in the form of temporary dipoles)
C9H20
-188
-138
-130
-95
-91
-57
-54
B.P.
-162
-89
-42
-0.5
36
69
98
126
151
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SIMPLE HYDROCARBONS
• Draw the structural formula, condensed
structural formula and molecular formula
for the following:
– propane
– Octane
Which should have the highest M.P & B.P.?
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