Why is $\ce{CF2Cl2}$ polar? The Lewis dot structure shows the molecule as being symmetric. Wouldn't that make it nonpolar?

  • 6
    $\begingroup$ The Lewis dot structure doesn't show a thing. It is drawn on a planar sheet of paper, and the real molecule is 3D. Ever heard of a tetrahedral geometry? $\endgroup$ – Ivan Neretin Oct 11 '17 at 4:28
  • 1
    $\begingroup$ I encourage you to make that as an answer @IvanNeretin. It seems to be a precise and complete answer to me. $\endgroup$ – Pritt says Reinstate Monica Oct 19 '17 at 5:53
  • $\begingroup$ @PrittBalagopal Maybe, but it is no improvement over the existing answer, hence no. $\endgroup$ – Ivan Neretin Oct 19 '17 at 6:23

The problem is that the first Lewis diagrams you learn to draw don't take 3D structure into account. A more realistic structure for dichlorodifluoromethane looks like

where the dashed wedged bond is meant to represent a single bond pointing away from you ("into" the plane of the screen), and the filled bold wedged bond is meant to represent a single bond pointing toward you (coming out of the screen). This is more than a traditional Lewis structure though, which is more about notating single/double/triple bonds and any nonbonding electrons.

You could also deduce the 3D structure from the fact that carbon centers with 4 separate bonds are always tetrahedral, and there is no way in a perfect tetrahedron to place either the 2 chlorines or the 2 fluorines exactly opposite each other. This means there is no way for the individual bond dipoles to cancel.


Not the answer you're looking for? Browse other questions tagged or ask your own question.