Cancelling dipole moments

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Annie Chantasirivisal_4G
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Cancelling dipole moments

Postby Annie Chantasirivisal_4G » Sat Nov 16, 2019 4:13 pm

I'm having trouble visualizing how dipole moments cancel each other out for molecules that have more than two dipoles.

I can kind of see how the C-Cl bonds in trans-dichloroethene cancel out, since they're on opposite sides and their vectors are going in opposite directions, but how do I visualize that for a compound like CCl3H?

Siddiq 1E
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Re: Cancelling dipole moments

Postby Siddiq 1E » Sat Nov 16, 2019 4:25 pm

I have the same problem... I usually draw it out but if it's too complicated I don't know what to do :(

Charlene Datu 2E
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Re: Cancelling dipole moments

Postby Charlene Datu 2E » Sat Nov 16, 2019 4:26 pm

You can first relate it to its structure, which is a tetrahedral. Since there are two chlorine atoms on opposite sides of each other, the two dipole moments will cancel each other out. However, since there is a third chlorine atom, that dipole moment will not be cancelled out, meaning that there is an imbalance of dipole moments. For CCl3H, this is a polar molecule, unlike the trans-dichloroethene you described.

I guess another way to look at it is to see whether or not the location of the dipoles are symmetrical at all points of symmetry. If you can draw a line down the middle at any point and have the same amount of dipole moments on either side, then the dipoles cancel out.

I hope that helped a bit :)

kristi le 2F
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Re: Cancelling dipole moments

Postby kristi le 2F » Sun Nov 17, 2019 8:39 pm

The dipoles will cancel if they are in opposite direction and of same magnitude. They will be same magnitude if they involve the same atoms. If the dipoles cancel, the resulting molecule will be non polar with polar bonds.

Chem_Mod
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Re: Cancelling dipole moments

Postby Chem_Mod » Sun Nov 17, 2019 8:51 pm

805317518 wrote:You can first relate it to its structure, which is a tetrahedral. Since there are two chlorine atoms on opposite sides of each other, the two dipole moments will cancel each other out. However, since there is a third chlorine atom, that dipole moment will not be cancelled out, meaning that there is an imbalance of dipole moments. For CCl3H, this is a polar molecule, unlike the trans-dichloroethene you described.

I guess another way to look at it is to see whether or not the location of the dipoles are symmetrical at all points of symmetry. If you can draw a line down the middle at any point and have the same amount of dipole moments on either side, then the dipoles cancel out.

I hope that helped a bit :)


To clarify, no two dipole moments in CHCl3 completely cancel each other out due to the tetrahedral arrangement of the atoms (this is why CH2Cl2 is also a polar molecule). Practice makes perfect when it comes to visualizing the 3-D orientation of molecules. I would suggest trying out websites that allow you to see molecules in 3D (try http://molview.org/) or finding a friend who owns a molecular model kit (many people taking organic chemistry have them).

Jacob Villar 2C
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Re: Cancelling dipole moments

Postby Jacob Villar 2C » Sun Nov 17, 2019 10:09 pm

A dipole moment can be considered cancellable if the dipole moments move in opposite directions, and their magnitude is the same.

Nathan Rothschild_2D
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Re: Cancelling dipole moments

Postby Nathan Rothschild_2D » Sun Nov 17, 2019 11:22 pm

Can someone give another example of a canceling dipole moment?

sarahwu3a
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Re: Cancelling dipole moments

Postby sarahwu3a » Mon Nov 18, 2019 11:16 pm

Another example of dipoles cancelling out is in CO2. The dipoles point in opposite directions and as they are the same magnitude, cancel out and CO2 is nonpolar.

Amy Kumar 1I
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Re: Cancelling dipole moments

Postby Amy Kumar 1I » Sun Dec 08, 2019 9:37 am

If the shape is tetrahedral and all attachments are the same, dipoles cancel.

EvaLi_3J
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Re: Cancelling dipole moments

Postby EvaLi_3J » Sun Dec 08, 2019 9:47 am

You don't have to determine whether it is polar or not by trying to cancel every single dipole moment. If there is no lone pair on the central atom and all the other atoms are the same, it is a non-polar atom. If there are two opposite lone-pairs and all the other atoms are the same, it is probably also non-polar.

DavidTabib 3H
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Re: Cancelling dipole moments

Postby DavidTabib 3H » Sat Oct 31, 2020 5:41 pm

Are there any exceptions to this?

Sana Nagori 2H
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Re: Cancelling dipole moments

Postby Sana Nagori 2H » Sat Oct 31, 2020 6:38 pm

When did we learn about dipole moments? Did I zone out during one of the lectures or is this from something else.


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