SCl2, SCl4, and SCl6 - which are polar

I know the answer is that the first two are polar - I just don't understand HOW you know that? Can someone please explain how to determine if a molecule is polar or not? Also, I would have to be able to answer this question without access to the electronegativity values, if that makes a difference.

Thank you in advance - this subject is baffling to me!

SCl6 is non-polar because it has 6 bonding pairs and no lone pairs, giving it an octahedral shape. When you draw the vectors, you can see that the resultant is 0, making it nonpolar. SCl4 on the other hand is polar because it has 4 bonding pairs and one lone pair, giving it a trigonal pyrimidal shape. When you draw vectors for this molecule you can see that the resultant displacement is <0, and therefore it is polar. SCl2 is also polar due to reasons similar to those in the case of SCl4.

Based on electronegativity, if the difference is 1.5 or more, the bond is polar. However, multiple bonds in different vectors with the same element cancel.
For example, CCl4 is polar, but CH2Cl2 is not, depending on the geometry (only if both Cl's are bonded on the same side is it polar).

Here's a few sites that might help explain it.
http://www.chemguide.co.uk/atoms/bonding…
http://www.mhhe.com/physsci/chemistry/an…
http://teacher.shaker.k12.nh.us/ahayward…

Hope this helps!!