Lab 7: Molecular Models
Chemistry 100
_____________________
Date ______________________
Section ______________________
Name
Pre-Lab Exercises
Lab 7: Molecular Models
1. For each of the following molecules, draw the structural formula (using your best three-dimensional artwork include any nonbonding electron pairs), then give the molecular geometry, the molecular shape, the
approximate bond angles in degrees, and tell whether or not the molecule is polar. These molecules all can be
found in your textbook (Ch. 5). Reminder: molecules that are linear, triangular planar and tetrahedral tend to be
non-polar; both of the bent shapes, as well as pyramidal molecules tend to be polar.
CH4
CO2
NH3
______________
_____________
______________
_____________
____________
H2O
Electron-dot
Structure
Molecular
shape
Polar/
nonpolar?
______________
Page 1 of 6
___________
___________
Lab 7: Molecular Models
Chemistry 100
Chemistry 100
Lab 7: Molecular Models
DISCUSSION
Molecular models are very useful because they give us a 3-dimensional representation of a molecule, which often makes
it easier to analyze intra- and inter-molecular forces. It was a 3-dimensional model that helped James Watson and
Francis Crick finally solve the mystery of DNA in 1953. Modeling is a powerful tool of scientific discovery which you will
get a chance to practice in this lab.
The color code of the molecular models we’ll be using is as follows. Use colored “atoms” for the following elements:
black = carbon; light blue = nitrogen; red = oxygen; white = hydrogen; green = chlorine. The holes in the “atoms” are
designed to give a reasonable approximation to the correct geometry or shape of a molecule. Use a short connector for
a single bond, two longer connectors for a double bond, and three longer connectors for a triple bond. Use the flat
pieces to represent nonbonding electron pairs. (The chlorine “atoms” do not have holes for the nonbonding electron
pairs to be attached, so omit them in your models and in your structural formulas.) In all the molecules studied in this
lab, all atoms have the usual number of bonds (carbon = 4, nitrogen = 3, oxygen = 2, hydrogen and chlorine = 1).
PROCEDURES
Diatomic Molecules
1. Draw structural formulas for H2, O2, N2, and Cl2. Include nonbonding electron pairs so that you can see that the
octet rule applies to all of them except H2.
2. Build models of these molecules, including the nonbonding electron pairs except in Cl2. Are these molecules
polar or nonpolar?
Simple Nonmetal Hydrides
1. Draw structural formulas for the simplest compounds containing the following elements. You need to figure out
how many hydrogen atoms to use based on the number of bonds carbon, nitrogen, oxygen, and chlorine
usually have.
a. carbon and hydrogen
b. nitrogen and hydrogen
c. oxygen and hydrogen
d. chlorine and hydrogen.
2. Build models, including nonbonding electron pairs except in (d). Give the molecular geometry and the
molecular shape for each molecule (except (d)), and tell whether it is polar or nonpolar (including (d)).
Hydrocarbons
Hydrocarbons are compounds containing only hydrogen and carbon. Regardless of their shape, they are nonpolar or
very slightly polar because the bond between carbon and hydrogen is only very slightly polar. When there are two or
more carbon atoms, there may be single bonds, double bonds, or triple bonds between the carbon atoms. You already
made a model of the simplest hydrocarbon in the previous section.
1. Draw structural formulas and build models for three different hydrocarbons that each contain two carbon atoms,
with single, double, and triple bonds between the carbon atoms, respectively. Use as many hydrogen atoms as
needed to get four bonds on each carbon atom. What is the shape around each carbon atom?
Page 2 of 6
Lab 7: Molecular Models
Chemistry 100
Chlorinated Hydrocarbons
Hydrocarbons that have one or more hydrogen atoms replaced by chlorine atoms are called chlorinated hydrocarbons or
chlorocarbons. (And when chlorine and fluorine atoms replace the hydrogen atoms, they are called chlorofluorocarbons,
or CFCs, a very important class of compounds with environmental implications).
1. Draw structural formulas and build models for CH4, CH3Cl, CH2Cl2, CHCl3 (called chloroform), and CCl4.
2. Note that if you draw the typical flat-looking structural formula for CH2Cl2, it appears that you can either place
the chlorine atoms opposite each other or adjacent to each other. Draw both of these structural formulas.
3. Look very carefully at the model and decide which, if either, is a good representation of the molecule.
4. Decide, based on whether or not the molecules are symmetrical, whether these molecules are polar or nonpolar.
Alcohols
Alcohols are similar to hydrocarbons in structure, but they have at least one O-H group bonded to a carbon atom in the
place of one of the hydrogen atoms.
1. Draw the following structural formulas
a. the simplest alcohol (it has only one carbon atom)
b. an alcohol with two carbon atoms and one O-H group
c. an alcohol with two carbon atoms with an O-H group on each carbon atom.
2. Build models of these three alcohols. Two of them are extremely poisonous, and the other is against the Word
of Wisdom! Are these molecules polar or non-polar? (The last one may appear to have a symmetrical
structural formula, but look at the model and consider the electronegativity of oxygen before making your
decision.)
Page 3 of 6
Lab 7: Molecular Models
Chemistry 100
_____________________
Lab Partner __________________
Date _____________________
Section _____________________
Name
Lab Station Check Out
#
REPORT
Diatomic Molecules
Initials
1. Draw the structural formulas and indicate whether each molecule is polar or non-polar.
2. Build the molecular models. Have the instructor or lab assistant inspect them and initial.
H2
O2
N2
Cl2
Structural
formulas
Polar or nonpolar?
Simple Nonmetal Hydrides
Initials
1. Draw the structural formulas and indicate whether each molecule is polar or non-polar.
2. Build the molecular models. Have the instructor or lab assistant inspect them and initial.
C and H
N and H
Structural
formulas
Molecular
Shape
Polar or nonpolar?
Page 4 of 6
O and H
Cl and H
Lab 7: Molecular Models
Chemistry 100
Hydrocarbons
Initials
1. Draw the structural formulas and indicate whether each molecule is polar or non-polar.
2. Build the molecular models. Have the instructor or lab assistant inspect them and initial.
C – C Single Bond
C = C Double Bond
C  C Triple Bond
Structural formulas
Shape around each
carbon atom
Chlorinated Hydrocarbons
Initials
1. Draw the structural formulas and indicate whether each molecule is polar or non-polar.
2. Build the molecular models. Have the instructor or lab assistant inspect them and initial.
CH4
CH3Cl
CHCl3
CCl4
Structural
formulas
Polar or nonpolar?
3. Draw 2 versions of a structural formula for the molecule CH2Cl2.
4. Draw a 3-dimensional perspective of each of the structures.
5. Based on the 3-D models, is CH2Cl2 polar or non-polar? ______________________________________
Structural Formulas
CH2Cl2 (1)
3-Dimensional Perspective
CH2Cl2 (2)
CH2Cl2 (1)
Page 5 of 6
CH2Cl2 (2)
Lab 7: Molecular Models
Chemistry 100
Alcohols
Initials
1. Draw the structural formulas and indicate whether each molecule is polar or non-polar.
2. Build the molecular models. Have the instructor or lab assistant inspect them and initial.
1 carbon, 1 –OH
2 carbons, 1 –OH
2 carbons, 2 –OH
Structural
formulas
Polar or nonpolar?
Post-Lab Analysis
1. Draw the structural formula of propylene glycol, a common food additive, component of deodorants and other
household products, and ingredient in nontoxic antifreeze. It is an alcohol with a three-carbon chain (with single
bonds) and O-H groups on two adjacent carbon atoms.
2. Propane and butane, common portable fuels, are C3H8 and C4H10, respectively. Draw their structural formulas.
Page 6 of 6