Transcript Chapter 21 Powerpoint

Hydrocarbons
Section 21.1 Introduction to
Hydrocarbons
Section 21.2 Alkanes
Section 21.3 Alkenes and Alkynes
Section 21.4 Hydrocarbon Isomers
Section 21.5 Aromatic
Hydrocarbons
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Section 21.1 Introduction to Hydrocarbons
• Explain the terms organic compound and organic
chemistry.
• Identify hydrocarbons and the models used to
represent them.
• Distinguish between saturated and unsaturated
hydrocarbons.
• Describe where hydrocarbons are obtained and how
they are separated.
microorganism: a tiny organism, such as a
bacterium or a protozoan, that cannot be seen
without a microscope
Section 21.1 Introduction to Hydrocarbons
(cont.)
organic compound
unsaturated hydrocarbon
hydrocarbon
fractional distillation
saturated hydrocarbon
cracking
Hydrocarbons are carbon-containing
organic compounds that provide a
source of energy and raw materials.
Organic Compounds
• Chemists in the early 19th century knew
living things produced a variety of carbon
compounds, called “organic” compounds.
• They were not able to synthesize them in the
lab and labeled them as mysterious.
• Wöhler was the first to produce an organic
compound in the lab.
Organic Compounds
(cont.)
• Organic compound is applied to all
carbon-containing compounds with the
primary exceptions of carbon oxides,
carbides, and carbonates, which are
considered inorganic.
• In organic compounds, carbon nearly always
shares its electrons and forms four covalent
bonds.
Organic Compounds
(cont.)
• Carbon atoms are bonded to
hydrogen atoms or other elements
near carbon on the periodic table.
• Carbon atoms also bond to other
carbon atoms and form long
chains.
Hydrocarbons
• The simplest organic compounds are
hydrocarbons, which consist of only the
elements carbon and hydrogen.
• There are thousands of hydrocarbons.
Hydrocarbons
(cont.)
• Carbon atoms bond to each other
by single, double, and triple
bonds.
• Saturated hydrocarbons contain
only single bonds.
• Unsaturated hydrocarbons
contain at least one double or
triple bond.
Refining Hydrocarbons
• Many hydrocarbons are obtained from the
fossil fuel petroleum.
• Fractional distillation involves boiling
petroleum and collecting each group of
components as they condense at different
temperatures.
Refining Hydrocarbons
(cont.)
Refining Hydrocarbons
(cont.)
• Fractional distillation towers do not yield
fractions in proportion to demand.
• Heavier fractions are converted to gasoline or
other lighter fractions by a process called
cracking.
Refining Hydrocarbons
(cont.)
• Gasoline is not a pure substance.
• Most molecules have 5 to 12 carbons.
• Gasoline is modified by adjusting its
composition to improve performance,
resulting in the octane rating system.
Section 21.1 Assessment
Petroleum is separated into usable parts
by boiling and condensing each
component in a process called ____.
A. cracking
B. fractional distillation
C. saturation
D. bonding
0%
0%
A
B
A.
B.
C.
0%
D.
C
A
B
C0%
D
D
Section 21.1 Assessment
What is a hydrocarbon that contains only
single bonds called?
A. unsaturated
B. organic
D
A
0%
C
D. fully bonded
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. saturated
Section 21.2 Alkanes
• Name alkanes by examining their structures.
• Draw the structure of an alkane when given its name.
• Describe the properties of alkanes.
IUPAC (International Union of Pure and Applied
Chemistry): an international group that aids
communication between chemists by setting rules
and standards in areas such as chemical
nomenclature, terminology, and standardized
methods
Section 21.2 Alkanes (cont.)
alkane
homologous series
parent chain
substituent group
cyclic hydrocarbon
cycloalkane
Alkanes are hydrocarbons that contain
only single bonds.
Straight-Chain Alkanes
• Alkanes are hydrocarbons that have only
single bonds between atoms.
Straight-Chain Alkanes (cont.)
• The names of alkanes end in –ane.
• Prefixes are derived from Greek numbers.
• A series of compounds that differ from one
another by a repeating unit is called a
homologous series.
Straight-Chain Alkanes (cont.)
Branched-Chain Alkanes
• Carbon atoms can bond to one, two, three,
or four other carbon atoms making a
variety of chains possible.
Branched-Chain Alkanes (cont.)
• Straight chains and branched chains can
have the same molecular formula.
• Order and arrangement of atoms in organic
compounds determine their identities.
• When naming branched chain alkanes, the
longest continuous chain of carbon atoms is
called the parent chain.
• All the side branches are known as
substituent groups.
Branched-Chain Alkanes (cont.)
Branched-Chain Alkanes (cont.)
• Naming branched-chain alkanes
− Count the number of carbon atoms in the longest
continuous chain.
− Number each carbon in the parent chain.
− Name each alkyl group substituent.
− If the same alkyl group appears more than once as
a branch on the parent structure, use a prefix to
indicate how many times it appears.
− When different alkyl groups are attached to the
same parent chain, place their names in
alphabetical order.
Branched-Chain Alkanes (cont.)
• Naming branched-chain alkanes
− Write the entire name, using hyphens to separate
numbers from words and commas to separate
numbers.
Cycloalkanes
• An organic compound that contains a
hydrocarbon ring is called a cyclic
hydrocarbon.
• Cyclic hydrocarbons with
only single bonds are called
cycloalkanes.
Cycloalkanes
(cont.)
• Naming substituted cycloalkanes is the
same as straight-chains but with a few
exceptions.
− The ring is always considered the parent chain.
− Numbering starts on the carbon that is bonded to
the substituent.
− When more than one carbon has a substituent,
number in the direction that gives the lowest
possible numbers for the substituents.
Properties of Alkanes
• Structure affects molecular properties.
• Alkanes are not polar and are good solvents
for other nonpolar molecules.
Properties of Alkanes (cont.)
• Physical properties of alkanes
− Compared to water,
methane boils and
melts and lower
temperatures.
− Methane molecules
have little
intermolecular
attraction compared to
water.
Properties of Alkanes (cont.)
• Chemical properties of alkanes
− Alkanes have low reactivity because they are
nonpolar and have no charge, and because they
have strong single bonds between carbon atoms.
Section 21.2 Assessment
What is a cyclic alkane with no
substituents groups and 6 carbon atoms?
A. heptane
B. cycloheptane
D
A
0%
C
D. cyclobutane
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. cyclohexane
Section 21.2 Assessment
Alkanes contain how many double
bonds?
A. greater than 2
B. 2
D
A
0%
C
D. 0
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. 1
Section 21.3 Alkenes and Alkynes
• Compare the properties of alkenes and alkynes with
those of alkanes.
• Describe the molecular structures of alkenes and
alkynes.
• Name an alkene or alkyne by examining its structure.
• Draw the structure of an alkene or alkyne by
analyzing its name.
hormone: chemical produced in one part of an
organism and transported to another part, where it
causes a physiological change
Section 21.3 Alkenes and Alkynes (cont.)
alkene
alkyne
Alkenes are hydrocarbons that contain
at least one double bond, and alkynes
are hydrocarbons that contain at least
one triple bond.
Alkenes
• Unsaturated hydrocarbons that contain at
least one or more double covalent bonds
between carbon atoms are called alkenes.
Alkenes (cont.)
• Alkenes are named in much
the same way as alkanes.
• Alkenes end in –ene.
• When four or more carbon
atoms are present, specify
the location of the double
bond.
Alkenes (cont.)
• When naming branched-chain alkenes,
follow the same rules as for alkanes, with
two exceptions.
− The parent chain is always the longest chain that
contains double bond, whether it is the longest
chain or not.
− The position of the double bond, not the branches,
determine the numbering.
− Use a prefix to designate the
number of double bonds.
Alkenes (cont.)
• Alkenes are nonpolar and have low
solubility in water.
• Alkenes are more reactive than alkanes
because the double bond increases electron
density between the two carbon atoms,
providing a good site for chemical reactivity.
Alkynes
• Unsaturated hydrocarbons that contain one
or more triple bonds between carbon
atoms are called alkynes.
Alkynes (cont.)
• Straight-chain and branched-chain alkynes
are named in the same way as alkenes,
except the ending is –yne.
Alkynes (cont.)
• Alkynes have physical and chemical
properties similar to alkenes but are
generally more reactive because the triple
bonds cause even larger electron densities
than double bonds.
Section 21.3 Assessment
Which of the following is generally the
most reactive?
A. cycloalkanes
B. alkanes
D
A
0%
C
D. alkynes
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. alkenes
Section 21.3 Assessment
What is the name of a straight-chain
hydrocarbon with six carbon atoms and a
triple bond between the second and third
carbon atoms?
A. 2-hexene
A
0%
D
D. 3-hexyne
C
C. 2-hexyne
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. 3-hexene
Section 21.4 Hydrocarbon Isomers
• Distinguish between the two main categories of
isomers—structural isomers and stereoisomers.
• Differentiate between geometric isomers with cisand transprefixes.
• Describe the structural variation in molecules that
results in optical isomers.
electromagnetic radiation: transverse waves that
carry energy through empty space
Section 21.4 Hydrocarbon Isomers (cont.)
isomer
chirality
structural isomer
asymmetric carbon
stereoisomer
optical isomer
geometric isomer
optical rotation
Some hydrocarbons have the same
molecular formula but have different
molecular structures.
Structural Isomers
• Isomers are two or more compounds that
have the same molecular formula but
different molecular structures.
• Structural isomers have the same chemical
formula but their atoms are bonded in
different arrangements.
Structural Isomers (cont.)
• There are two main classes of isomers:
structural isomers and stereoisomers.
• Structural isomers have different physical and
chemical properties.
• The structure of a substance determines
properties.
Stereoisomers
• Stereoisomers are isomers in which all
atoms are bonded in the same order but
are arranged differently in space.
Stereoisomers (cont.)
• Geometric isomers result from different
arrangements of groups around a double
bond.
• Cis means on the same side, and trans
means across from.
• Geometric isomers have different physical and
chemical properties.
Stereoisomers (cont.)
Chirality
• Louis Pasteur discovered two forms of
crystallized tartaric acid.
• The forms were mirror images of each other
called right and left-handed forms.
• The property in which
a molecule exists in
right and left-handed
forms is called
chirality.
Optical Isomers
• Chirality occurs whenever a compound
contains an asymmetric carbon.
• Asymmetric carbon is a carbon atom that
has four different atoms or groups attached
to it.
• The four groups can be arranged in two
different ways.
Optical Isomers (cont.)
• Isomers that result from different
arrangements of four different groups
around a carbon atom represent the other
class of stereoisomers, called optical
isomers.
• Optical isomers have the same physical and
chemical properties except in chemical
reactions where chirality is important.
Optical Isomers (cont.)
• When polarized light passes through a
solution containing an optical isomer, the
plane of polarization is rotated to the right
by the D-isomer and to the left by the Lisomer, producing and effect called optical
rotation.
Optical Isomers (cont.)
Section 21.4 Assessment
What are two molecules with the same
formula but different structures called?
A. isotopes
B. chiral
D
A
0%
C
D. asymmetric
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. isomers
Section 21.4 Assessment
Which type of substances have the same
physical and chemical properties but
produce different optical rotations?
A. isomers
A
0%
D
D. optical isomers
C
C. isotopes
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. geometric isomers
Section 21.5 Aromatic Hydrocarbons
• Compare and contrast
the properties of
aromatic and aliphatic
hydrocarbons.
• Explain what a
carcinogen is, and list
some examples.
hybrid orbitals: equivalent
atomic orbitals that form
during bonding by the
rearrangement of valence
electrons
aromatic compound
aliphatic compound
Aromatic hydrocarbons are unusually
stable compounds with ring
structures in which electrons are
shared by many atoms.
The Structure of Benzene
• Even by the middle of the 19th century,
hydrocarbon ring structures remained
unknown.
• Michael Faraday first isolated benzene in
1825.
• Chemists knew the formula was C6H6 and
proposed several possible models which
would have all be very reactive, but benzene
is unusually stable.
The Structure of Benzene (cont.)
• German chemist Friederich Kekulé claimed
to have had a dream in which he realized
the flat, hexagonal shape ring structure for
benzene.
• Kekulé’s structure explained some of
benzene's properties, but not its lack of
reactivity.
The Structure of Benzene (cont.)
• Linus Pauling’s hybrid orbital theory
explained benzenes lack of reactivity.
• The double bonds in benzene are not fixed,
but rather the electrons are delocalized and
shared among all six carbon atoms.
Aromatic Compounds
• Organic compounds that contain benzene
rings as part of their structure are called
aromatic compounds.
• Aromatic was originally used because many
benzene related compounds were found in
pleasant smelling oils that came from plants
and plant parts.
Aromatic Compounds
(cont.)
• Aliphatic compounds are the alkane,
alkene, and alkyne hydrocarbons, coming
from the Greek word for fat because they
were obtained by heating animal fat.
Aromatic Compounds
(cont.)
• Substituted benzene compounds are
named in the same way as cyclic alkanes.
Aromatic Compounds
(cont.)
• Many aromatic compounds were
commonly used as industrial and
laboratory solvents.
• Health risks linked to aromatics include
respiratory ailments, liver problems, and
damage to the nervous system.
• Some aromatic compounds cause cancer.
Section 21.5 Assessment
Aliphatic compounds were originally
obtained from ____.
A. fossil fuels
B. animal fats
D
A
0%
C
D. minerals
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. plant oils
Section 21.5 Assessment
Which is NOT true of benzene?
A. It is an aromatic compound.
B. It has a flat hexagonal shape.
D
A
0%
C
D. It has delocalized electrons.
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. The double bonds make it
unstable.
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Section 21.1 Introduction to
Hydrocarbons
Key Concepts
• Organic compounds contain the element carbon,
which is able to form straight chains and branched
chains.
• Hydrocarbons are organic substances composed of
carbon and hydrogen.
• The major sources of hydrocarbons are petroleum and
natural gas.
• Petroleum can be separated into components by the
process of fractional distillation.
Section 21.2 Alkanes
Key Concepts
• Alkanes contain only single bonds between carbon
atoms.
• Alkanes and other organic compounds are best
represented by structural formulas and can be named
using systematic rules determined by the International
Union of Pure and Applied Chemistry (IUPAC).
• Alkanes that contain hydrocarbon rings are called
cyclic alkanes.
Section 21.3 Alkenes and Alkynes
Key Concepts
• Alkenes and alkynes are hydrocarbons that contain
at least one double or triple bond, respectively.
• Alkenes and alkynes are nonpolar compounds with
greater reactivity than alkanes but with other properties
similar to those of alkanes.
Section 21.4 Hydrocarbon Isomers
Key Concepts
• Isomers are two or more compounds with the same
molecular formula but different molecular structures.
• Structural isomers differ in the order in which atoms are
bonded to each other.
• Stereoisomers have all atoms bonded in the same
order but arranged differently in space.
Section 21.5 Aromatic Hydrocarbons
Key Concepts
• Aromatic hydrocarbons contain benzene rings as
part of their molecular structures.
• The electrons in aromatic hydrocarbons are shared
evenly over the entire benzene ring.
Organic compounds must contain which
elements?
A. carbon
B. oxygen
D
A
0%
C
D. nitrogen
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. hydrogen
Cyclohexane contains how many
hydrogen atoms?
A. 6
B. 12
D
A
0%
C
D. 20
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. 14
Which of the following has the greatest
reactivity?
A. benzene
B. hexane
D
A
0%
C
D. hexyne
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. hexene
A carbon bonded to four different groups
is ____.
A. cyclic
B. aromatic
D
A
0%
C
D. left-handed
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. asymmetric
Where were aromatic compounds
originally obtained from?
A. fossil fuels
B. plant oils, plant parts, and spices
D
A
0%
C
D. minerals
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. animal fats
Molecules that have the same formula and
the atoms are bonded in the same order
but are arranged differently in space, and
have different properties are ____.
A. structural isomers
A
0%
D
D. sterioisotopes
C
C. optical isomer
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. geometric isomers
If n is the number of carbon atoms in a
hydrocarbon, what is the general formula
of a cyclic alkane?
A. CnHn+2
A
0%
D
D. CnH2n
C
C. CnHn
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. CnH2n+2
Which does NOT describe what happens
as a liquid freezes?
A. The temperature of the system
is increased.
D
D. The molecules begin to form
a lattice.
A
0%
C
C. The liquid is entering the
solid phase.
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. Energy is released by the
system.
What is a series of compounds that differ
from one another by a repeating unit
called?
A. heterogeneous series
A
0%
D
D. branched-chain series
C
C. straight-chain series
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. homologous series
What structural characteristic do all
aromatic compounds share?
A. They are composed of
cyclohexane.
D
0%
A
D. They contain a cyclic
alkane.
C
C. They contain a benzene
ring.
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. They have a triple bond.
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Table 21.5
Examples of Alkenes
Table 21.6
Examples of Alkynes
Figure 21.17 Isomers of Pentane
Figure 21.25 Sigma- and Pi-bonding in Benzene
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