2E #25a CH2Cl2 Lewis dot Structure

[Immi Lee - 1D]

The question asks whether CH2Cl2 is polar/nonpolar. According to the answer key, the molecule is polar due to the dipole moments not canceling out, and depicts the lewis dot structure with H on the top and the right and Cl on the left and the bottom. I never usually draw CH2Cl2 this way, and usually have the Cl opposite of each other, but if I draw it this way the dipoles look like they cancel out. Was there a rule that I missed somewhere? I never would have determined CH2Cl2 as a polar molecule without looking at the answer key.

[IsaacLaw1E]

You have to remember that Lewis Dot Structures are 2D representations of 3D objects. In reality, it doesn't matter which way you draw the Lewis structure, because the VSEPR model for a tetrahedron will be the same either way. This is also why CH2Cl2 is polar even though the dipoles on the Lewis structure cancels out; the dipoles on the VSEPR model don't cancel because of its 3D shape.

[Valerie Doan 3I]

Isaac is correct. You probably thought that the two Cl atoms were in the axial positions and therefore their dipoles cancelled. However that is not the case. Because there are 4 bonding pairs, VSEPR tells us that it is tetrahedral. So, only one atom is in the axial position and the three other atoms are equatorial. With this arrangement, the dipoles do not cancel. Here is an image that may help you visualize:

[Sahaj Patel Lec3DisK]

Exactly what Isaac said. Whenever there are dipole vectors or polarity in play, then the molecule is likely polar. The way CH2Cl2 is actually structured is by having the Cls on one side and the Hs on the other. When drawn this way, the diploe moments do not cancel out. If it was nonpolar, no matter how you drew one of the correct structures, then the diploes will cancel out. Since the diploes do not cancel out in this version of CH2Cl2, then it will be polar.