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Problem: Predict whether each molecule is polar and show the direction of bond dipoles and the molecular dipole when applicable:
(a) Ammonia, NH 3 (b) Boron trifluoride, BF 3 (c) Carbonyl sulfide, COS (atom sequence SCO)
Plan: Find the molecular shape. From EN’s, find the direction of the bond dipoles and see if they balance each other in the molecule.
Solution: (a) For NH 3. Molecular shape is trigonal pyramidal. - N is more EN than H, so the bond dipoles point toward N. - The bond dipoles reinforce each other.
- Thus the molecular dipole points toward N:
Therefore, ammonia is a polar molecule.
Skill 10-6. Using molecular shape and electronegativity values to predict the direction of a molecular dipole
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