Constructing Molecular Models
Chemistry 11
Purpose:
Name: _______________
To use a molecular model kit to construct models of molecules with different types of
covalent bonds - single, double, and triple.
Use these models to visualize the three-dimensional shapes of the molecules.
Introduction: Molecules have three-dimensional shapes which depend on the ways in which the atoms in
the molecules are bonded together. Many molecular model kits use coloured balls and
-connectors to represent atoms and bonds. A structure formed by joining these balls and
connectors will approximate the shape of a molecule.
The "atoms" in a molecular model kit are frequently colour coded:
H - white
C - black
O - red
S - yellow
N - orange
Halogens - green
In a molecular model, if two balls are joined together by a connector, the connector represents a
covalent bond composed of two electrons. If two balls are joined together by two connectors, a double
covalent bond (two electron pairs) is indicated. Three connectors joining two balls represent a triple
covalent bond (three electron pairs).
The molecule can be represented using a
1.
Lewis diagram (shows the valence electrons for each atom in the molecule)
2.
Structural formula (shows the arrangement of atoms in the molecule using lines to represent
covalent bonds – 1 line for single, = 2 lines for double and ≡ for triple bond). Only the bonded
electrons are shown using the lines for bonds.
Apparatus: Molecular model kit
Procedure:
A. First, familiarize yourself with the pieces in your model kit. Identify by their colours the types of
atoms you have available. For each part of the activity, construct molecular models and draw the
two representations discussed above for each molecule (Some structures may have double or triple
bonds. Use the proper number of connectors to join atoms in each model.
B. H2, Br2, and HCl
C. Methane (CH4) and carbon tetrachloride (CCl4)
D. Ammonia (NH3).
E. Water (H2O) and dichlorine monoxide (Cl2O)
F. Oxygen (O2), carbon dioxide (CO2), and ethene (C2H4)
G. Nitrogen (N2), hydrogen cyanide (HCN), and ethyne (C2H2)
Section
B
Compound
H2
B
Br2
B
HCl
C
CH4
C
CCl4
D
NH3
E
H2O
E
Cl2O
Lewis Structure
Structural formula
Name of shape
F
CO2
F
O2
F
C2H4
G
N2
G
HCN
G
C2H2
EXAMINING THE OBSERVATIONS
1. What type of bond is involved in the models you constructed in parts B, C, D, and E?
2. What type of bond is common to the three models you constructed in part F?
3. What type of bond is common to the three models you constructed in part G?
4. Which of the models that you constructed represent diatomic molecules? What type of shape do
they have? Explain why these would be the same for all diatomic molecules.
5. Which of the models that you constructed could be described as bent? What is unique about their
type of bonding?
6. Describe the shape of ammonia.
7. Which of the models that you constructed could be described as linear? Are there any similarities
in the models you described as linear?
8. On the basis of your results, list all bond combinations must be present in order for a triatomic
molecule to be linear?
FOR FURTHER THOUGHT
9. Which (if any) of your models contained one or more balls with a hole that is not connected to any
other atom? What would this situation represent?
10. Why do you think you were instructed to use as many connectors as possible to join atoms in each
model?