Cancelling Dipole Moments

[salvadorramos3k]

Can somebody please explain to me when dipole moments cancel out? Is it only when the surrounding atoms are all the same and the moment is going away from the central atom? For example, I thought CH2Cl2 would cancel dipole moments since Cl has two atoms pulling away from the central atom, but turns out there is still a dipole moment. Why? Thank you :)

[AnvitaaAnandkumar_1B]

In general, the molecule doesn't have a net dipole when the orientation of species around the molecule is symmetrical, resulting in a cancelling of dipole moments.
In the case of a tetrahedral geometry, the molecule only doesn't have dipole moment when all four species surrounding the central atom are the same, like CH4 or CF4.
Therefore, CH2Cl2 does have net dipole moment, as no orientation of the molecules results in a cancellation of the dipoles.

[Kishan Shah 2G]

Can someone explain more in depth why CH2Cl2 is polar?

[Amy Luu 2G]

CH2Cl2 is a tetrahedral so the atoms are not directly opposite of each other. For example, you would think that the H are on opposite sides which would cancel out the dipole moment. However, since in a tetrahedral, the angle between the atoms are 109.5 degrees, no atom would be directly opposite to another. Therefore, there will be dipole moments and the molecule will be polar.

[Kassidy Ford 1I]

Since in tetrahedral molecules there are no molecules directly opposite one another, the only way it will be nonpolar is if all of the surrounding atoms are the same