Transcript Unit 6 Chapter 10 Introduction to Organic Chemistry: Alkanes

Unit 6
Chapter 10
Introduction to
Organic Chemistry
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
1
Organic Chemistry
Why is it important?
>90% of compounds are organic
What is an organic compound
• is a compound made from carbon atoms.
• has one or more C atoms.
• has many H atoms.
• may also contain O, S, N, and halogens.
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Organic Compounds
Typical organic compounds
• have covalent bonds.
• have low melting points.
• have low boiling points.
• are flammable.
• are soluble in nonpolar
solvents.
oil (organic) and water (inorganic)
• are not soluble in water.
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Organic vs. Inorganic
• Propane, C3H8, is an
organic compound used
as a fuel.
• NaCl, salt, is an inorganic
compound composed of
Na+ and Cl- ions.
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Comparing Organic and
Inorganic Compounds
Copyright © 2005 by Pearson Education, Inc.
Publishing as Benjamin Cummings
5
Learning Check
Identify each characteristic as most typical of compounds
that are 1) inorganic 2) organic.
A. has a high melting point
B. is not soluble in water
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2
C. has a formula CH3─CH2─CH3
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D. has a formula MgCl2
2
E. burns easily in air
F. has covalent bonds
2
2 (some 1)
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Writing Formulas for Alkanes
In organic compounds
• carbon has 4 valence electrons and hydrogen has 1.
•
•C•
H•
•
• to achieve an octet, C forms four bonds.
H
H

HCH
H
C
H

H
H
CH4 , methane
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Tetrahedral Structure of Carbon
A carbon
atom with four
single,
covalent
bonds, has a
tetrahedral
shape.
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Organic Molecules
In organic molecules,
• valence electrons are shared.
• covalent bonds form between carbon atoms.
• C-C bonds are very strong, can form long chains.
H H
•• ••
HCCH
•• ••
H H
H
H
H
C
C
H
H
H
ethane, CH3─CH3
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Tetrahedral Structure of Carbon
In molecules with
two or more carbon
atoms, each
carbon atom with
four single bonds
has a tetrahedral
shape.
(Rotation,
Maximum space)
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Alkanes
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Education, Inc.
Publishing as Benjamin Cummings
•Compounds containing only C and H
•All bonds are single bonds (2 electrons are shared)
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Structural Formulas
Alkanes are written with structural formulas that are
• expanded to show each bond (Lewis Structure).
• condensed to show each carbon atom and hydrogen
atoms attached to that carbon.
Expanded (Lewis)
H
H
C
H
Condensed
CH4 , methane
H
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Expanded and Condensed
Structures
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Structural Formulas
Condensed formulas are written for expanded structural
formula by showing each carbon and the attached
hydrogen atoms.
Expanded
Condensed
H H H H
│ │ │ │
H─C ─C ─C ─C ─ H
│ │ │ │
H H H H
CH3─CH2─CH2─CH3
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Names of Alkanes
The names of alkanes
• are determined by the IUPAC (International Union of
Pure and Applied Chemistry) system.
• end in –ane.
• with 1-4 carbons in a chain use prefixes as follows.
Name
# Carbons
Structural Formula
Methane
1
CH4
Ethane
2
CH3CH3
Propane
3
CH3CH2CH3
Butane
4
CH3CH2CH2CH3
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Names of Alkanes
Alkanes with 5-10 carbon atoms in a chain use Greek
prefixes.
Name
# Carbons
Structural Formula
Pentane 5
CH3CH2CH2CH2CH3
Hexane 6
CH3CH2CH2CH2CH2CH3
Heptane 7
CH3CH2CH2CH2CH2CH2CH3
Octane
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CH3CH2CH2CH2CH2CH2CH2CH3
Nonane 9
CH3 CH2 CH2CH2CH2CH2CH2CH2CH3
Decane 10 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Know the 1st eight alkanes (name and structure)
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Learning Check
A. Write the condensed formula for:
H H
H
H
H
H
C
C
C
C
C
H
H
H
H
H
H
B. What is its molecular formula?
CH3─CH2─CH2─CH2─CH3
C5H12
(Gives total # of each atom, does not indicate how they are arranged)
C. What is its name? pentane
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Some Structures for Butane
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Hexane has Six Carbon Atoms
Hexane
• is an alkane with six carbon atoms in a continuous
chain.
• has a “zig-zag” look because each carbon atom is at
the center of a tetrahedron.
• is represented by a ball-and-stick model as shown
below.
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Cycloalkanes
Cycloalkanes
• are cyclic alkanes.
• have two hydrogen atoms fewer than the open chain.
(remember each carbon has 4 bonds)
• are named by using the prefix cyclo- before the name
of the alkane chain with the same number of carbon
atoms.
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Cycloalkanes
The structural formulas of cycloalkanes are usually
represented by geometric figures,
Cyclopropane
CH2
CH2
Cyclobutane
CH2
CH2
CH2
CH2
CH2
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More Cycloalkanes
Cyclopentane
CH2
CH2
CH2
CH2
CH2
Cyclohexane
CH2
CH2 CH2
CH2
CH2
CH2
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Properties of Alkanes
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Publishing as Benjamin Cummings
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Some Properties of Alkanes
Alkanes are
• nonpolar.
• insoluble in water.
• less dense than water.
• flammable in air.
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Some Properties of Alkanes
Alkanes with 1-4 carbon
atoms are
• methane, ethane,
propane, and butane.
• gases at room
temperature.
• used as heating fuels.
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Some Properties of Alkanes
Alkanes with 5-8 carbon atoms are
• liquids at room temperature.
• pentane, hexane, heptane, and octane.
• very volatile.
• used to make gasoline.
Alkanes with 9-17 carbon atoms
• are liquids at room temperature
• have higher boiling points.
• are found in kerosene, diesel, and jet fuels.
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Some Properties of Alkanes
Alkanes with 18 or more carbon atoms
• have high molar masses.
• are waxy solids at room temperature.
• used in waxy coatings of fruits and
vegetables.
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Combustion
In combustion reactions,
• alkanes react with oxygen.
• CO2, H2O and energy are produced.
Alkane + O2
CO2 + H2O + heat
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Learning Check
Write a balanced equation for the
complete combustion of propane.
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Solution
Unbalanced equation
C3H8 + O2
CO2 + H2O
First: Balance C
C3H8 + O2
3CO2 + H2O
Then: Balance H
C3H8 + O2
3CO2 + 4H2O
Last: Balance O
C3H8 + 5O2
3CO2 + 4H2O (Balanced)
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