Modeling Molecules

Introduction:

You can represent a molecule two-dimensionally, as a structural formula or electron dot structure. Although such models are useful in certain contexts, they do not accurately represent bond angles between atoms or shapes of molecules. In this activity, you will construct three-dimensional models of several molecules. You will use electron dot structures and structural formulas to inform how you construct the three-dimensional models.

Materials:

jelly beans, gum drops, or gumballs; toothpicks; twist ties; colored pencils or crayons

Procedure:

1.  Identify the chemical and structural formulas and electron dot structures of the following molecules:

sulfur hexachloride, carbon dioxide, methylcyclohexane, propane, ethene, phenol

2.  Write the formulas and draw the two-dimensional structures in the table.

3.  Chose one color candy to represent each atom of an element (e.g., red jelly bean = hydrogen). Create a key that identifies each element.

4.  Use the candy, toothpicks, and/or twist ties to construct a three- dimensional model of each of the aforementioned molecules.

5.  Draw, as accurately as possible, each model in the table. Identify all bond angles of each molecular drawing and write the molecular shape(s) beneath the drawing.

6.  Answer the questions.

Table:

Molecule name / Chemical formula / Electron dot structure / Structural formula / Drawing of model

Key:

Questions:

1.  Compare the information provided by a molecule’s chemical formula to the information provided by its structural formula.

2.  Identify the bond types between the carbon and the two oxygen atoms in the carbon dioxide molecule. Describe the bond angles. Explain how the structural formula can be used to help determine the bond angles.

3.  What is the major difference between the two-dimensional and three- dimensional models of propane and ethene? When might you choose to use a two-dimensional model rather than a three-dimensional model when representing one of the molecules?

4.  Explain how the VSEPR theory can be used to predict the shapes of molecules.

5.  Use the Internet to research how chemists know that an oxygen molecule has unpaired electrons. Summarize the reason in a sentence or two.