unit 6 chapter 10 introduction to organic chemistry copyright © 2005 by pearson education, inc....
TRANSCRIPT
Unit 6Chapter 10
Introduction to Organic Chemistry
Copyright © 2005 by Pearson Education, Inc.Publishing as Benjamin Cummings
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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.
• are not soluble in water.oil (organic) and water (inorganic)
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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
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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
C. has a formula CH3─CH2─CH3
D. has a formula MgCl2
E. burns easily in air
F. has covalent bonds
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1
2
2
2
2 (some 1)
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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
Writing Formulas for Alkanes
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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 H • • • •
H C C H H C C H
• • • • H 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
Copyright © 2005 by Pearson 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) Condensed
H
H C H 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 CH3─CH2─CH2─CH3
│ │ │ │ H H H H
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Names of AlkanesThe 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
Methane1 CH4
Ethane 2 CH3CH3
Propane 3 CH3CH2CH3
Butane 4 CH3CH2CH2CH3
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Names of AlkanesAlkanes 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 8 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?
(Gives total # of each atom, does not indicate how they are arranged)
C. What is its name?
CH3─CH2─CH2─CH2─CH3
C5H12
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 CH2
CyclobutaneCH2 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
Copyright © 2005 by Pearson Education, Inc.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 AlkanesAlkanes 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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