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Topic: A stupid question on bond polarity  (Read 1629 times)

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Offline startanewww

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A stupid question on bond polarity
« on: September 17, 2012, 09:20:13 AM »
Non-polar means no net positive or negative poles are formed. Then does non-polar mean neutral?
My book mentions that "In a experiment, a charged rod is placed close to a jet of liquid (e.g. water). If the liquid is deflected from its vertical path towards the rod, the liquid contains polar molecules. If the liquid shows no deflection, it contains only non-polar molecules."
But my teacher said that non-polar molecules could also deflect a polar liquid, just to a lesser degree when compared to polar molecules.
So can non-polar mean neutral?

Offline Schrödinger

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Re: A stupid question on bond polarity
« Reply #1 on: September 17, 2012, 09:52:00 AM »
Non-polar inevitably means neutral. I mean, you can't have a net charge on your molecule and expect it be non-polar.

But what your teacher meant was different. Consider water. It's a polar liquid. Hence the attraction towards the rod. Now consider CCl4. It's a non-polar molecule. But its bonds are polar. It's just that the dipole moment vectors of each bond are symmetrically oriented and hence they all tend to cancel out. or CO2 for that matter.

As a matter of fact, this very property is used to separate N2 and CO2 from each other via selective adsorption. Although CO2 doesn't have a net dipole moment, when subjected to an external charge, it is possible that this symmetry of arrangement gets disturbed.
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