I have a chemistry question on polarity?

Question

I have this lab to do, but I don't really understand. My question is what is the polarity of p-dichlorobenzene, silicon dioxide, and tin. Thanks.

Answer 1

The previous answer is not right.

A molecule is polar when it has polar covalent bonds AND the geometry of the molecule is such that the dipole moments of the individual bonds do not cancel out.

A covalent bond will be polar (even slightly) when you have atoms of different elements bonding together. So even the bond C-H is a polar bond. The degree of polarization depends on the difference of electronegativity. The bigger the difference the more polar the bond. E.g. C-H is slightly polar because the difference in the electronegativity of C and H is small.

If you look at the structure of p-dichlorobenzene (e.g. go to wikipedia) you will see that the molecule is symmetrical. Thus, although you have polar bonds like the C-Cl which are quite polar, the dipole moments of the bonds cancel out each other, because of the symmetry and thus the molecule has a 0 net dipole momement and it is non-polar.

Si belongs in the same family as C. Thus it is tetravalent and SiO2 has a similar structure as CO2. Specifically it is
O=Si=O. It is linear with two identical polar bonds with opposite direction. Thus the sum of the dipole moments of the bonds is 0 and the molecule is non-polar.

Tin is an element. It is not bonded to anything else so there are no polar bonds and thus it is non-polar.

Answer 2

Find the molecular structres of each of the molecules. A good place to go is Wikipedia.....here's the link for dichlorobenzene: http://en.wikipedia.org/wiki/P-dichlorobenzene. Basically, look to see what the structure of each molecule is. The more C-Hs it has, the less polar it is. So, a molecule that is all C-H will be super non-polar. Benzene rings are also relatively nonpolar (because they're mostly C-H).

Now, the more O a molecule has, the more polar it is. If a benzene ring has O on it, it will be more polar. Silicon dioxide's formula is SiO2, which would lead me to believe that it is polar.

Tin is just Sn, a metal, so it's probably not polar. In order for something to be polar, it needs to be connected to another molecule because polarity is based upon electronegativity. Sn is obviuosly not bonded to anything else, so you can't judge its electronegativity and therefore can't judge if it's polar. I could be wrong with this, though---I haven't had to deal with the polarity of non-organic molecules, so this info about tin here is just my best guess.

For more info on polarity, go here: