Explain how lone pairs compress bond angles
Three steps, the way the exam actually works: work through the lab, write down your own measurements, 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 numbers will cost you the point — exactly as it would with a real reader.
Predict before you look
- VSEPR treats electron regions as mutually repelling. Does a lone pair take up MORE space near the central atom than a bonding pair, or less?
- Ideal tetrahedral geometry is 109.5°. If a lone pair pushes harder than a bond does, will the remaining bond angles come out larger or smaller than that?
Nothing to submit here — these are to think through, so the prediction below is an informed one rather than a guess.
Commit to an answer now. It is not graded and being wrong costs nothing — the point is to have something specific to reconcile against once you have the data.
Answer every prediction to unlock the lab. A sentence is enough.
Run the investigation
Predictions first
The procedure and the simulation unlock once you have committed above. Observing before predicting is how a wrong intuition survives a lab intact.
Record what you measured
These are your numbers, not ours. The grader sees them, so your conclusions have to follow from what you actually recorded.
| Bond angle in the tetrahedral example | ° |
|---|---|
| Bond angle in the trigonal pyramidal example | ° |
| Bond angle in the bent example | ° |
| Lone pairs on the trigonal pyramidal central atom | |
| Lone pairs on the bent central atom |
Answer the free response
The VSEPR model predicts both shape and angle distortion. (a) Starting from the ideal tetrahedral angle, explain why the angle becomes smaller in a trigonal pyramidal molecule and smaller still in a bent molecule with the same electron-domain geometry. (b) Distinguish electron-domain geometry from molecular geometry using one of your examples. (c) Explain why lone-pair repulsion is stronger than bonding-pair repulsion. (d) A student says the shape of a molecule can be predicted by counting atoms attached to the center and ignoring lone pairs. Evaluate that claim using your recorded structures.
Sign in to have this graded and saved to your progress.