Question

How can you tell if a molecule is polar or nonpolar?

Answer 1

I believe it has something to do with VSEPR theory?

Answer 2

You need to look at a few things. Are there any electronegative atoms? Is there any inductive effect? Is there any VESPR stuff creating asymetrical molecules?

Answer 3

For example BF3 looks like this:
http://en.wikipedia.org/wiki/File:Polarity_boron_trifluoride.png

It's trigonal planar, so all the electronegative F's pull in the same direction and cancel each other out.

Answer 4

(so it's nonpolar)