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Topic: Dipole Moment  (Read 3308 times)

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Offline aysenrmusa

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Dipole Moment
« on: February 03, 2018, 09:53:29 PM »
Hi everyone!

I am a bit confused about figuring the strength of dipole moments in different compounds that are not necessarily in the same group.

For example;

List the following molecules in order of increasing dipole moment: H2O, CBr4, H2S, HF, NH3, CO2

The answer is: HF>H2O>NH3>H2S and CBr4 and CO2 are apparently nonpolar.


Offline Enthalpy

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Re: Dipole Moment
« Reply #1 on: February 04, 2018, 07:39:28 PM »
You can know the non-polar molecules from their symmetry.

For some others, I'd check published data. Can someone do it better?

Depending on the data source, HF can have a stronger or weaker moment than H2O.

Offline Hacktacular

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Re: Dipole Moment
« Reply #2 on: February 23, 2018, 11:23:46 AM »
I'd agree with you enthalpy,

I had it explained as being a bit of a dark art.  Apart from molecular symmetry there's also differences in electronegativity to consider hence HF being the most polar (linear with an 'electron hog' on one side).  Electronegativity differences also account for water being more polar than ammonia: even though ammonia is pyramidal with an electron pair at the top making it seemingly quite polar, water trumps it due to oxygen being more electronegative than nitrogen.

In the end it's a balance between shape and electronegativity or, quite simply, a dark art.

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