Relate 3D molecular shape to bond angle and polarity
Three steps, the way the exam actually works: work through the lab, write down your own observations, then answer a 6-point free response. What you recorded goes to the grader with your writing, so a conclusion that does not follow from your own evidence will cost you the point — exactly as it would with a real reader.
Run the investigation
- 1Open water, methane, and carbon dioxide in the viewer.
- 2Rotate each molecule until you can clearly compare the arrangement of atoms around the central atom.
- 3Record the observed shape of each and the approximate bond angle information visible in the model.
- 4Use those structures to decide whether the bond dipoles cancel or reinforce.
Booting the lab…
Record what you found
This is your reading of the source, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| Shape of H2O | |
|---|---|
| Shape of CH4 | |
| Shape of CO2 | |
| Approximate H–O–H bond angle | ° |
| Approximate H–C–H bond angle | ° |
| Approximate O–C–O bond angle | ° |
Answer the free response
The same atoms can produce very different molecular behavior because of shape. (a) Using your three molecules, explain why methane is nonpolar even though each C–H bond has some electron density difference, while water is polar. (b) Compare water’s bond angle with methane’s and explain what that difference says about lone-pair repulsion. (c) Explain why carbon dioxide is nonpolar even though each C=O bond is polar. (d) A student says molecular polarity can be decided from bond polarity alone without drawing a shape. Use your data to evaluate that claim.
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