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Why some molecules with polar bona do not have permanent dipoles

I've been looking through the specification for the AQA AS Chemistry and seen that it says:

Students should be able to:

-explain why some molecules with polar bonds do not have a permanent dipole

Please could some explain why? Thanks very much :smile:
Reply 1
Avatar for JN17
JN17
10
Although the bonds are polar, if the molecule is symmetrical then the dipoles "cancel" eachother and there is no overall dipole on the molecule.
Original post by Yesitisi
This is due to the symmetry in some polar molecules,so the dipoles cancel each other out.

For example, water is a polar molecule, however, as water is negatively charged on one side and positively charged on the other, the charges cancel each other out.


Isn't water a polar molecule? It has a 'bent' shape so the charges cannot cancel out.
Reply 3
Avatar for nicoleb132
nicoleb132
OP
Original post by JN17
Although the bonds are polar, if the molecule is symmetrical then the dipoles "cancel" eachother and there is no overall dipole on the molecule.


thank you very much! what would be a good example of a molecule like this?
Reply 4
Avatar for JN17
JN17
10
Original post by nicoleb132
.

CO2 is a good example, the C=O bond is polar, however the molecule is linear, so if you look at the central carbon, it has a delta - on either side of it, so they cancel eachother and the overall molecule has no permanent dipole.
More complicated ones would be something like SF6, the S-F bond is polar but the octahedral shape is symmetrical about the central S atom, so there is no overall dipole.
Reply 5
Avatar for nicoleb132
nicoleb132
OP
Original post by JN17
CO2 is a good example, the C=O bond is polar, however the molecule is linear, so if you look at the central carbon, it has a delta - on either side of it, so they cancel eachother and the overall molecule has no permanent dipole.
More complicated ones would be something like SF6, the S-F bond is polar but the octahedral shape is symmetrical about the central S atom, so there is no overall dipole.



thank you very much! at my school we didn't get taught any of the bonding topic!!
Original post by nicoleb132
thank you very much! at my school we didn't get taught any of the bonding topic!!


I feel for you.. We weren't taught any inorganic chemistry like halogens etc..

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