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

[dentalgirlyay]

How can one tell if a molecule is polar or nonpolar? I know many people have said that if its symmetrical it is most likely nonpolar, and if it is nonsymmetrical it is polar, but sometimes its not true! so i need to know how can u know for sure? and how do u determine its net dipole? 🙁

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[sugarsting]

You need to add up the dipoles using vector addition. How you do this is first determine which bonds are polar (the two atoms connected differ in their electronegativity by a significant amount). Then look at what the molecule looks like. If all those dipoles cancel out because the molecule is symmetrical, then it is nonpolar even though it has polar bonds.

Example. CH4...technically the C-H bond is a little polar because the carbon is more electronegative than the hydrogen. So if you drew the dipople it would have the negative side pointing at the C and the positive side pointing at the H. But methane is tetrahedral, and each bond angle is the same (109.5 deg), so all the dipoles cancel out.

The net dipole is the overall effect of doing the vector addition of the bond dipoles. This is generally done visually. The net dipole will be so that the side with more electronegative atoms is the more negative side of the dipole.

 

[joonkimdds]

if you learned physics, it would be super easy to understand.
Recall X and Y vectors.
U move up 3, down 4, where are you? if you are not at the starting point, then that's dipole moment. (answer = u moved down 1, thus dipole)

 

[Contach]

if you learned physics, it would be super easy to understand.

if you learned chemistry it would be super easy......