Chemistry

Goal: Create examples of the geometrical shapes possible for simple central-atom molecules.

Materials and Equipment:

• Toothpicks
• Gum drops of three different colors. Determine which color will represent the central atom, which will represent lone electron pairs and which will represent terminal atoms.

Procedure

1. Using the diagrams in your text, create models for central atoms with only bond pairs (no lone pairs) for AX₂, AX₃, AX₄, AX₅, and AX₆ configurations. Use the gumdrop colors you designated for central and terminal "atoms". Identify each resulting shape with the configuration (i.e., AX₂ is linear).
   1. For each model, list how many atoms are involved (total gumdrops)
   2. For each model, list how many bonds are involved (total number of toothpicks).
   3. Are all your models symmetrical, or do you have more than one model for any configuration?
2. Using the diagrams in your text, create models for molecules with one or more lone pairs around the central atom (using a different color for the lone pairs) for each of the 5 above pair configurations (AX₂ to AX₆).
   1. For each model, list how many atoms are involved (total central atom/terminal atom gumdrops).
   2. For each model, list how many lone pairs are involved (total lone pair gumdrops).
   3. For each model, list how many bonds are involved (total number of toothpicks).
   4. Which models have different shapes for the same number of terminal atoms? Do these have the same number of lone pairs?
   5. How many shapes are possible for a molecule with 2 terminal atoms? 3? 4? 5? 6?
   6. Which models are asymmetrical (and therefore likely to be polar)?
   7. Which of your asymmetrical models could be non-polar under the right conditions (the same elements are placed on opposite sides of the central atom)?
   8. Which of your models will always be polar?
3. Be sure that you properly dispose of the toothpicks when you are done with your modeling exercise!

Report

1. Describe your procedure and identify the colors you used with the type of thing represented.
2. Report your survey results (answers to the questions above). Arrange your data in an appropriate tabular format to make comparisons easy.
3. Explain how molecules with the same number of terminal atoms such as AX₃ can have different shapes.

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