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Shape and Polarity (Bond polarities) watch

1. Why do the bond polarities cancel out in molecules such as BCl3 and SO3? And also, why do the bond polarities cancel in a molecule of CO2 but not in H2O? (Apparently this is because of symmetry, but dont both of these molecules seem to be symmetrical in shape?)
2. Try drawing in the dipole moments for each bond...as CO2 is linear the dipoles point in opposite directions canceling each other out. In water it's bent so the dipoles arn't opposite to each other thus water is polar
3. H20 has 2 lone pairs, so it's non-linear. Therefore, the molecule isn't symmetrical, so the polar bonds don't cancel out.
4. (Original post by malteser12345)
Why do the bond polarities cancel out in molecules such as BCl3 and SO3? And also, why do the bond polarities cancel in a molecule of CO2 but not in H2O? (Apparently this is because of symmetry, but dont both of these molecules seem to be symmetrical in shape?)
bond polarities cancel out in molecules BCl3 and SO3 because for a molecule to be polar, there has to be a positive end and a negative end, if u draw out these 2 molecules, both ends will be slightly negative, there is no positive end, just 2 negative ends, its only a positive centre, hence the molecule isnt polar
5. (Original post by malteser12345)
Why do the bond polarities cancel out in molecules such as BCl3 and SO3? And also, why do the bond polarities cancel in a molecule of CO2 but not in H2O? (Apparently this is because of symmetry, but dont both of these molecules seem to be symmetrical in shape?)
Have you done vectors and vector addition in maths yet?

If so, draw a dipole vector from each negatively charged atom to each positively charged atom. Then add them up using vector addition, you'll be able to tell straight away whether something will possess a net dipole or not.
6. (Original post by malteser12345)
Why do the bond polarities cancel out in molecules such as BCl3 and SO3? And also, why do the bond polarities cancel in a molecule of CO2 but not in H2O? (Apparently this is because of symmetry, but dont both of these molecules seem to be symmetrical in shape?)
I posted this about 1 month ago:

7. Wow, thanks for all the replies and all the help!

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