Cancelling dipole moments

[Annie Chantasirivisal_4G]

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]

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]

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]

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]

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]

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

[Nathan Rothschild_2D]

Can someone give another example of a canceling dipole moment?

[sarahwu3a]

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]

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

[EvaLi_3J]

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]

Are there any exceptions to this?

[Sana Nagori 2H]

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