How to identify polarity

(Polar molecules, Non-polar molecules, etc.)

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melissa_dis4K
Posts: 106
Joined: Fri Sep 28, 2018 12:28 am

How to identify polarity

Postby melissa_dis4K » Wed Nov 28, 2018 10:08 pm

I'm having a lot of trouble understanding polarity, can someone please help and explain how it is that we identify polar molecules. I know that polar is the unequal sharing of electrons and that if the dipole moments cancel it is nonpolar. However, I am just having trouble applying it to the actual structures. And does the structure matter when cancelling out polarity? For example, if it's bent does it not cancel, like in H2O?

Patrick Cai 1L
Posts: 93
Joined: Fri Sep 28, 2018 12:25 am

Re: How to identify polarity

Postby Patrick Cai 1L » Wed Nov 28, 2018 10:19 pm

Polar molecules have one thing in common: a net nonzero dipole moment. To determine the dipole moment, one must consider the spatial distribution of the atoms and electron clouds, as well as the differences in electronegativity between the bonded atoms. For instance, in the case of H2O, both the electronegativity difference between hydrogen and oxygen and the bent molecular shape of H2O contribute to the molecule's polarity.

Jeffrey Xiao 4A
Posts: 35
Joined: Fri Sep 28, 2018 12:28 am
Been upvoted: 1 time

Re: How to identify polarity

Postby Jeffrey Xiao 4A » Wed Nov 28, 2018 10:53 pm

Usually lone pairs make the molecule polar but there are exceptions with the linear AX2E3 and square planar AX4E2 where the molecules are nonpolar because dipole moments cancel regardless of the lone pairs,
Otherwise, all the shapes with no lone pairs are nonpolar (tetrahedral, trigonal planar, octahedral, etc) IF the bonded atoms are all the same (CCl4 or CH4) not (CH2Cl2 or CH3Cl) which are polar.


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