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Topic: How do you know when a molecule is polar?  (Read 14072 times)

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Leen

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How do you know when a molecule is polar?
« on: October 07, 2005, 07:19:39 PM »
I know that the larger a molecule is, the less polar it is.  But how do you know when a molecule is too large? for example, benzoic acid consists of a benzene ring and then a COOH which is polar, but since there are already 7 carbons, doesn't the polar functional group lose its affect?
Also, if a molecule can hydrogen bond, is it automatically considered polar?

Offline madscientist

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Re:How do you know when a molecule is polar?
« Reply #1 on: October 07, 2005, 09:37:26 PM »
If you have a particular question your trying to answer, state it, with your working so far and we will all have a crack at it for you.

cheers,

madscientist :albert:
The only stupid question is a question not asked.

Leen

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Re:How do you know when a molecule is polar?
« Reply #2 on: October 07, 2005, 10:38:00 PM »
Alright, is benzoic acid a polar molecule? It's got a polar funcitonal group (COOH) so can it hydrogen bond?

Offline mike

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Re:How do you know when a molecule is polar?
« Reply #3 on: October 07, 2005, 10:43:20 PM »
Yes it is polar, as you stated, you are right it can hydrogen bond. :)
There is no science without fancy, and no art without facts.

Offline maxyoung

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Re:How do you know when a molecule is polar?
« Reply #4 on: October 08, 2005, 03:28:54 AM »
I know that the larger a molecule is, the less polar it is.  But how do you know when a molecule is too large? for example, benzoic acid consists of a benzene ring and then a COOH which is polar, but since there are already 7 carbons, doesn't the polar functional group lose its affect?
Also, if a molecule can hydrogen bond, is it automatically considered polar?

Hydrogen bonding and polar functional groups don't necessarily mean that the molecule is polar. You need to consider symmetry of the molecule as well. for example, CCl4 and benzene-1,3,5-triol have very polar functional groups ( the C-Cl, PH-OH bond are quite polar, and later has hydrogen bond as well), yet they are nonpolar molecules.

Offline Mitch

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Re:How do you know when a molecule is polar?
« Reply #5 on: October 08, 2005, 05:42:19 AM »
Hydrogen bonding and polar functional groups don't necessarily mean that the molecule is polar. You need to consider symmetry of the molecule as well. for example, CCl4 and benzene-1,3,5-triol have very polar functional groups ( the C-Cl, PH-OH bond are quite polar, and later has hydrogen bond as well), yet they are nonpolar molecules.

You get 5 extra scooby snacks for that answer. Great post! ;)
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