1

Lab Activity No. 6

MODELLING MOLECULAR SHAPES

OBJECTIVE: In this experiment, students will build models for molecular shapes using

plastic balloons for electron groups.

MATERIALS: tubes of plastic balloon and narrow straws (for inflating balloons) or latex

balloons

SAFETY PRECAUTIONS:

Plastic balloon is polyvinyl chloride dissolved in ethyl acetate, an ester with many

uses, such as artificial fruit essences and aroma enhancers, artificial flavors for

confectionery, ice cream and cakes, as a solvent in many applications (including

decaffeinating tea and coffee) for varnishes and paints (nail varnish remover), and for

the manufacture of printing inks and perfumes.

OPEN ALL WINDOWS TO ENSURE PROPER VENTILATION!

PROCEDURE:

1. Blow 2- to 3-inch diameter balloons.

2. Connect two balloons together to represent the behavior of two electron groups in an

atom (in a molecule)

3. Connect three balloons such that one balloon is in contact with the other two. This

represents the arrangement of three electron groups.

4. Connect four balloons such that one balloon is in contact the other three to model the

shape of four electron groups.

5. Draw the three structures you have created.

6. Redraw the structures with straight lines (bonds) originating from the point of

intersection of the balloons and outward cutting through the balloon. (For the 2-

balloon model, there should be 2 lines, 3 balloons, 3 lines etc.)

7. Measure the (bond) angles between any two adjacent lines.

QUESTIONS:

1. How would you describe the shape of the balloon structures you made?

2. What are the bond angles in the structures? Would the bond angles be all the same

whichever pair of bonds you measure?

3. Think of any object that can represent each of the structures you made?

4. Given the Lewis structures of the following molecules, what molecular geometry and

bond angles would you predict?

2

Group No. _____ Date: _______

Names: _____________________________

_____________________________

_____________________________

MODELLING MOLECULAR SHAPES

Number of electron

groups Balloon drawing Stick drawing

3

1. How would you describe the shape of the balloon structures you made?

2. What are the bond angles in the structures? Would the bond angles be all the same

whichever pair of bonds you measure?

2 electron clouds ________________________

3 electron clouds ________________________

4 electron clouds ________________________

3. Think of any object that can represent each of the structures you made?

4. Given the Lewis structures of the following molecules, what molecular geometry and

bond angles would you predict?

H O H

O C O

O O O

C Cl

Cl

F

F