How do you determine the direction of polarity of a molecule?

[CrazCo]

and how do you figure out their structural shape?

 

I don't understand how you can just tell either of these two things and looking at this list of molecules I have to answer these questions too is might discouraging. Anyone with any pointers?

[hermanntrude]

have you ever studied vectors in another course? If you have, then this should be fairly easy. If not it can still be done.

 

Now first you'll need to know how to tell if a bond is polar. Can you do that?

 

If you can, then you need to figure out a few things:

 

1) are the dipoles on the bonds all the same size as each other?

2) are they evenly spaced around the central atom? Usually this is true only if there are NO lone pairs on the central atom, or if it is square planar.

 

If the molecule contains bonds with dipoles on them AND the answers to either questions 1 or 2 are "no" then the molecule is polar. If the molecule either does not contain bonds with dipoles OR it does AND the answers to questions 1 AND 2 are both "yes" then the molecule is non-polar.

 

Let me know if you have any further difficulty or more questions.

[CrazCo]

Thanks . I get that. What I don't get is, when something is polar, how to determine which direction the dipoles are pulling the most.

 

Example: HCN goes to the right because the electronegativities progressively increase.

[hermanntrude]

the dipole on a bond is due to the difference in electronegativities of the atoms at either end of the bond. The dipole pulls in the direction of the most electronegative atom. Once you have summed the vectors of those dipoles to get the resultant dipole it will show you the direction of the resultant.