polarity and molecular shape lab

Introduction: In this lab we learned to build models of molecules in order to determine the shape and polarity of each molecule. To find the shape of a molecule you need to look at the number of bonding pairs and the number of un-bonded pairs. You can determine these pairs by looking at the lewis structure of the molecule. From the pairs you can determine the shape of the molecule. To find the polarity of a molecule you need to make a ball/stick model. If the ball/stick model contains exposed positive or negative ends you will know that the molecule is polar. We constructed models of molecules to determine the molecular shape and predict the polarity of each molecule.


Materials: Molecular model kit.
Pencil and paper.
Camera.
Brains.

Procedure: We built a model for each of the molecules listed on the data table on the back of our lab paper. Next we drew the three-dimensional structure of each molecule in Table 1, using solid lines to represent bonds in the plane of the paper, dashed lines for bonds that point back from the plane of the paper, and wedged lines for bonds that point out from the plane of the paper toward the viewer. Then we noted the shape of each molecule in the third column of Table 1, the bond angles in column 4, whether or not they will be polar in column 5, and whether or not they exhibit resonance structure in column 6.

The Ball and Stick Models of Each Molecule:

C3H8:

CO2:

SF6:

IF3:

C2H4:

H2O:

H2O2:

N2:

CH4:

SiH2O:

HF:

SeF4:

SO3-2

 

BF3:

CH3NH2:

Conclusion: This experiment has taught us not only how to build a ball/stick model but also how to identify the shapes and the polarity of molecules. When you draw the lewis structure by itself it is more difficult to determine whether there are exposed positive or negative ends. Also, when you only draw the molecule on paper it is only in 2-D which makes it more difficult to see what the shape of the molecule truly is. Making the ball/stick model allows you to see the shape in 3-D which allows you to see the actual shape rather than try to imagine what it might look like in 3-D. This lab has been successful in teaching us about polarity and the shape of molecules.