Having trouble with Chemistry... How can I figure out polar and non-polar shapes and stuff?

Question

Are there any good relatively simple sites where I can find this out?

Also any info on solubility curves please.

Thanks!

Answer 1

It's very easy to figure out if a molecule is polar. It will be polar if it contains bonds between different kinds of nuclei, since each different nucleus has its own electronegativity. The exception to this is if the molecule is symetrical ie, you can draw mirror planes across it such that the effects of the polar bonds all cancel each other out. BCl3 is an example of this. It is a flat trigonal arrangment of atoms, and while each B-Cl bond is polarised such that the electron density is towards the chlorine, the overall polarity of the molecule is zero, because the polarity of all the bonds are acting against each other, such that they cancel out.

Water, on the other hand, is polar. if it were a linear molecule: H-O-H, then it would be symetrical, and the two bonds would cancel their polarity. HOWEVER, the water molecule is bent:

H H
O

Therefore, the two polar bonds do not act directly against each other, and there is thus net polarity in the molecule.

A pure hydrocarbon- ie, a molecule containing only C-H bonds, may suffer from a lack of overall symmetry, but it can always be considered non-polar anyway, because the polarity of the C-H bond is insignificant (though it is sufficient to cause chemoselectivity in certain reactions).