[cliverlong]

I was looking in a UK A Level text (AQA) and it explained the polar nature of some covalent bonds, such as HF or HCl being due to diiferences in the electronegativity of the atoms. Molecules of the same element such as F₂ and H₂ have no difference in electronegativity so the molecule is not polar. All very nice.

However, in the chapter it considered di-chloromethane. The statement was this is a polar molecule because the C-H bonds are not ploar. However, looking at the provided tables of electronegativity the difference between C and H was very close to the difference in e.n. between C and Cl. So the argument about electronegativity difference explaining bond (and hence molecule) polarity seems a bit weak to me.

Is something else going on, is e.n. a poor explanation or am I working from a table of "poor" e.n. values?


Regards

Clive

[P]

The chlorine is alot more electronegative that the H atoms on the carbon. You will get a delta negative region on the clorine and delta positive on the hydrogens as their electrons are drawn into the molecule towards the chlorine  -  thus the dipole.