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ORGANIC MODEL BUILDING &
HOMOLOGOUS SERIES
In this experiment, you will build models for molecules in which carbon atoms may
bond with each other as well as with atoms of other elements. Each carbon atom, however, may make only four covalent bonds. When carbon atoms bond with each other,
they form a carbon chain. Compounds containing carbon chains may become a
homologous series.
A homologous series is a set of compounds that conform to a general mathematical
ratio and general structure. As you build models of the members of some homologous
series, you will discover some series contain functional groups.
A functional group is responsible for characteristic properties and reactions. You can
recognize a functional group by the collection and arrangement of specific atoms. You
will learn more about the characteristic functional groups in this unit.
Equipment and Supplies:
per Lab Station ball and stick molecular model kit
What to Do
Obtain a ball and stick model kit. The instruction sheet in the box lists the color code for the
balls. Let one ball represent an atom. A stick is used to show one covalent bond. Springs are used to
represent two or more bonds between the same two atoms.
1.
2. Make a model of methane, CH4. Record the structural formula in Data Chart I.
3. Make models of successive members of the series in which the hydrocarbon, methane, is the
first member. (A hydrocarbon is a compound composed of hydrogen and carbon only.) Record on
data table.
DATA CHART I
Alkane Series CnH2n+2
Member
Molecular Formula
Structural Formula
Name
4.
First
methane
Second
ethane
Third
propane
Fourth
butane
Study Data Chart I and answer the following questions:
(a) For every additional carbon atom, how many hydrogen atoms are needed?
(b) The consecutive members of the homologous series differ by —CH2. Does ethane belong
to a homologous series?
Select two carbon atoms and connect them by two springs. Complete the model by adding as
many hydrogen atoms as possible. The model represents a molecule of ethene, also called ethylene,
the first member of the Alkene Series. Record the structural formula in Data Chart II.
5.
DATA TABLE II
Alkene Series
Member
Molecular Formula
CnH2n
Structural Formula
First
Name
ethene
(ethylene)
Second
propene
(propylene)
Third
butene
(butylene)
6. Continue to add carbon atoms until all of the information for Data Chart II has been found.
Keep the pair of double-bonded carbon atoms at one end of the molecular model. The other carbon
bonds are single bonds
7.
Study Data Chart II and answer the questions. Are the members of the Alkene Series members
of a homologous series?
How do you know?
8.
Make a model for a methanol molecule. Methanol is an alcohol whose structural formula is
H
│
The O-H is known as a
H ― C― O ―H
functional group; it is found in all alcohols.
│
H
9. Continue to add carbon atoms until all of the information for the Data Chart below has been found.
Keep the —0-—H group in all of your models. Write the structural formulas for the models you make.
Member
Molecular
Formula
DATA CHART
Structural Formula
Name
First
Methanol (methyl alcohol)
Second
Ethanol (ethyl alcohol)
Third
Propanol (propyl alcohol)
Fourth
Butanol (butyl alcohol)
10. Study the models of the alcohols you made. Are they members of a homologous series?
Explain
**
REMOVE ALL PEGS AND SPRINGS FROM THE BALLS. PUT AWAY THE BALL & STICK
MODEL KIT AND CONTINUE TO WORK ON THE BALANCE OF THE LAB.
Questions to Answer
1.
How is the presence of only single-bonded
carbon atoms in a homologous series
indicated in the name of
(a) the series?
(b) the name of a member of the series?
2.
How is the presence of one double bond in
the carbon chain indicated in the name of a
homologous series?
3. Study the Data Chart for the Alkene Series.
(a) Is there any member of this series that
does not have twice as many hydrogen atoms
as carbon atoms?
(b) The general formula for the Alkene
Series is CnH2n. What does this formula tell
you?
Is the general formula a formula for a single
compound or does it apply to every member
of the series?
4. Study the Data Chart for the Alkane Series.
(a) In the formula for ethane, are there exactly
twice as many hydrogen atoms as carbon
atoms?
Are there more than twice as many carbon
atoms?
If so, how many?
(b) How many carbon atoms are in a
molecule of propane?
How many hydrogen atoms?
Do you think that the general formula for the
Alkane Series might be CnH2n ?
Explain.
5. The general formula for the Ethyne Series is
CnH2n-2. What does this formula tell you about
the formula for any member of this series?
6. The name ending of the Alkyne Series indicates a triple bond in the carbon chain. Write
the formulas for the first four members of this
series:
Explain.
MOLECULAR FORMULA
Ethyne
STRUCTURAL FORMULA
Ethyne
Butyne
Propyne
Butyne
Propyne
Pentyne
Pentyne
7. Complete the Table.
Name of Series
Name endings of
Members
General Formula
for Series
Bonding in the
Carbon Chain
Alkane
Alkene
Alkyne
1. Do you think that there can be a homologous
series of alcohols containing two OH groups?
Explain.
2. What would be the general formula for a
homologous series in which a bromine atom
has been substituted for one hydrogen atom
in Alkane compounds?
NAMING HYDROCARBONS
The name for a hydrocarbon generally consists of two parts.
The first part indicates the number of carbon atoms in the chain:
1
2
3
4
5
C atom
C atoms
C atoms
C atoms
C atoms
meth
eth
prop
but
pent
6 C atoms
7 C atoms
8 C atoms
9 C atoms
10 C atoms
hex
hept
oct
non
dec
The second part of the name of a hydrocarbon is the same as that of its series. When you know
the series to which a hydrocarbon belongs, you have other information available:
Series
Name Ending
General Formula
Bonding In C Chain
Alkane
ane
CnH 2n+2
single bonds only
Alkene
ene
CnH 2n
one double bond
Alkyne
yne
CnH 2n-2
one triple bond
You will use the above information as you answer the questions in this Exercise.
1. How many carbon atoms are in each hydrocarbon?
(a) methane
(f) hexane
(k) decane
(b) ethane
(g) ethyne
(l) butyne
(c) ethane
(h) propane
(m) butene
(d) pentane
(i) heptane
(n) propyne
(e) propene
(j) octene
(o) butane
2.
For each compound listed below, underline the name ending, then fill in the blanks with the
indicated information:
COMPOUND
methane
butene
propyne
pentane
octane
NUMBER OF
C ATOMS
SERIES TO
WHICH IT
BELONGS
GENERAL
FORMULA OF
THE SERIES
COMPOUND
NUMBER OF
C ATOMS
SERIES TO
WHICH IT
BELONGS
GENERAL
FORMULA OF
THE SERIES
heptene
propene
butyne
decane
nonane
heptane
ethyne
hexyne
ethene
propane
3. Name each of the formulas by first writing down the carbon-count “prefix,” then add the ending
indicating the series to which the compound belongs:
C2H2
C2H4
C5H12
C3H4
C3H8
C4H6
C2H2
C6H12
CH4
C8H18
C3H6
C10H18
C7H12
C2H6
C5H10
4. Write the structural formula for each of the following:
(a) propane
(d) butene
(b) ethyne
(e) propene
(c) pentyne
(f) butyne
(g) methane
(j) ethane
(h) ethane
(k) propyne
(i) pentane
(l) pentene
5. Name the compound represented by:
H
(a) H—C ≡ C—H
H H H H
│ │ │ │
(c) H―C―C―C―C―H
│ │ │ │
H H H H
H H H H
│ │ │ │
(e) H―C―C―C―C═ C ― H
│ │ │
│
H H H
H
(b)
H H
│ │
C = C—C―H
│
H
H
H
│
(d) H―C―H
│
H
(a)
(b)
(c)
(d)
(e)
ISOMERS
Two builders can use the same amount of materials but construct two houses with different
structures. Chemists can take the same amounts of the same elements and bond them together in
different arrangements. The different arrangements produce compounds that have completely
different properties.
Molecules that have the same number of atoms of each element but different arrangements of
atoms are called isomers.
CHEMICAL HIDE AND SEEK
Compounds are classified according to the functional group or groups that are present in their
molecular structure.
Some classes of compounds and their functional groups are:
Alcohol —0—H
Acid —C—O—H
O
H
Amine —N
H
Aldehyde ―C―H
║
O
O
║
Ketone ―C―C―C―
O
║
Ester —C—O
Ether —C—O—C—
Other compounds are classified according to the bonding between carbon atoms in hydrocarbons:
Alkanes ―C—C―
Alkenes —C = C—
Alkynes —C ≡ C—
The object of Chemical Hide and Seek is to find the hidden clues (functional groups or carbon to
carbon bonding) and writing the name of the class of compound beside each “formula.”
Find and name the functional group in the formulas given and name the compound.
H H
│ │
1) H―C―C―H
│ │
H H
2)
H H
│ │
H―C―C―H
│ │
H O―H
H
│
3) H―C═ O
H O
H
│ ║
│
4) H―C―C―O―C―H
│
│
H
H
H O H
│ ║ │
5) H―C―C ―C―H
│
│
H
H
H H
│ │
6) H―C―C―N
│ │
H H
H
H
H
H
H
│
│ │
7) H―C――C――C―H
│
│
H
H
H―C―H
│
O―H
H
8)
H
H H O
│ │ ║
N―C―C―C―O―H
│ │
H H
H
│
9) O═C―H
H H O H
│ │ ║ │
10) H―C―C―C―C―H
│ │
│
H H
│
H―C―H
│
H
H O―H H
│ │
│
14) H―C―C―――C―H
│ │
│
H H
O―H
H H
H
│ │
│
15) H―C―C―C ≡C―C―H
│ │
│
H H
H
H H
H
H
│ │
│
│
16) H―O―C―C ―――C―――C―H
│ │
│
│
H H H―C―H H
│
H
17)
11)
H
│
H― C―O―H
│
H― C―O―H
│
H― C―O―H
│
H
H
│
H ― C ―H
12)
13)
H
│
H― C
│
H
C═O
O H
║ │
H―O―C―C―H
│
H
18)
H
│
O H
│ │
H― C―C―H
│ │
H H
H H H H H
│ │ │ │ │
H―C―C―C ―C ═ C―H
│ │ │
H H H
H H
H
│ │
│
19) H―C―C―O ―C―H
│ │
│
H H
H
H O
H H H
│ ║
│ │ │
20) H―C―C ―O ―C ― C―C―H
│
│ │ │
H
H H H