Dipole moments

[Tianna Nguyen 1I]

Hi, how do we tell if dipole moments cancel out and if a molecule is polar? Like for example HCBr₂Cl?

[Jason Ho 2L]

The first step would be to draw out the Lewis structure and then identify the molecular geometry. Once you know the shape, look at the atoms and determine the dipoles, if there are any. Dipoles of the same magnitude in opposite directions will cancel (or the net dipole movement is zero). If there is a net dipole movement, meaning the dipoles did not cancel out due to molecular shape or different strength of dipoles, then the molecule is polar.

[Sanjana Sivakumar 2E]

Hello!

I agree with Jason, but I just wanted to add in some pictures, so that it might be easier to understand.

In the first image, the Oxygen pulls the most on both Hydrogen atoms. Therefore, the hydrogens can't pull as much. The overall net dipole moment is towards the oxygen. And so it's polar.

In the second image, the net dipole moments cancel out, since each blue molecule is equally pulling on the red molecule.

Hope this helps!

[Emily Hou 1H]

Dipoles cancel out if the net dipole moment is zero. Using lewis structures and molecular geometry will help you see if dipoles in opposite directions will cancel. The dipoles that cancel should have the same magnitude meaning the same bonding atoms involved.

[NaomiAbramowicz1H]

Here are some general guidelines: it is polar if the molecule is not symmetrical or there are lone pairs on the central atom.

[Clayton Dinh 3C]

I think the best way to figure our polarity is to figure out the structure and seeing if dipoles moments cancel out due to being the same magnitude in different directions. Usually the molecule is polar if the shape isn't symmetrical when you draw it out.

[Melody_Tapia_1J]

first of all, the molecular shape is really important. This lets us know where -if any- the dipole moments cancel out. (you could figure this out by using the VSEPR model) Another important thing is to know which element has a higher electronegativity in order to determine if there are net charges.

[Joan Moci 1J]

First you would determine the structure and then the shape of the molecule using VSEPR. Then you would see which atoms are more atoms are more electronegative and if the dipoles cancel out, allowing you to determine whether or not the molecule is polar. In HCBr2Cl, the shape would be tetrahedral and since the dipoles don't cancel out as they are not the same atoms surrounding the central atom, the molecule is polar.