Molecular models of neutral molecules

Experiment 1Molecular Models of Neutral Molecules Experiment Inventory

Materials Colored Pencils

35 Marshmallows (Miniature)

Permanent Marker

35 Toothpicks

*Camera (camera phone is fine)

Labware Protractor

Note: You must provide the materials listed in *red.

EXPERIMENT 1: MOLECULAR MODELS OF NEUTRAL MOLECULES In this experiment, you will predict the three-dimensional geometry of a series of neutral molecules using the VSEPR theory.

PROCEDURE Part 1: The Periodic Table

1. Use the Periodic Table of Elements to determine the elemental symbol, group number, and valence electrons for the elements listed in Table 1 on the Experiment 1 Data Sheet. Record this data in Table 1.

2. Use colored pencils and the data in Table 1 to sketch a Lewis Dot Structure for each element in Table 1 on the Data Sheet.

Part 2: Construction of Molecules

1. Now, construct the three-dimensional geometry for the molecules listed in Table 2 on the Data Sheet. While you are constructing your molecules, keep the following points in mind:

• Nature “loves” symmetry, which means equal bond lengths and angles.

• Electrons prefer to be as far apart from each other as possible without disrupting the symmetry too drastically.

• Lone pairs take up more space because they are not confined by bonds, and are localized.

2. Look at Table 2 on the Data Sheet, and fill in the bond angles for each molecule you will be building.

Hint: Use the column in Table 2 on the Data Sheet labeled “Structure” to determine the molecular geometry.

3. Using colored pencils, make a Lewis Dot Structure sketch for each molecule in Table 2 you will be building. Remember to include your name and lab access code handwritten in the sketch.

4. Gather as many marshmallows and toothpicks you will need for building your first molecule (carbon dioxide).

Hint: You will need two marshmallows for the oxygen (O), and one marshmallow for the carbon (C).

5. Using the permanent marker, label the miniature marshmallow with the elemental symbol for each atom in your molecule (Figure 19).

6. Refer to the first column in Table 2 to determine the central atom in your molecule.

7. Connect the atoms together with toothpicks.

8. Compare your model with the diagram of the Linear molecular geometry in Table 2.

9. Use your protractor to verify that you have constructed your molecule with the correct bond angles.

10. To determine the angle between your atoms, place the center of the protractor on the central atom, and align the base with a bond (Figure 19). Then measure the angle. When in doubt, think “Should this angle be bigger or smaller than 90°?”

11. If your bond angles are incorrect, remove the toothpicks from the marshmallows, construct the molecule again, and use your protractor to verify that you have constructed your molecule with the correct bond angles.

12. Follow the above procedures for each molecule in Table 2.

13. When you are finished, take a picture of the molecules. Remember to include your name and lab access code handwritten in the background of the photo.

Figure 19: To satisfy the octet rule, the linear carbon dioxide molecule has double bonds. Note, the bond angles should be 180 degrees.