Molecular shape and polarity

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

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Melody Haratian 2J
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Molecular shape and polarity

Postby Melody Haratian 2J » Sun Dec 06, 2020 1:33 pm

For molecules with lone pairs of electrons on the central atoms, are they typically polar or nonpolar?
Is there a way to use the shape of molecules with lone pairs on the central atom to determine the polarity of the molecule?
Thanks!

Hannah Biju 1E
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Joined: Wed Sep 30, 2020 9:55 pm

Re: Molecular shape and polarity

Postby Hannah Biju 1E » Sun Dec 06, 2020 1:37 pm

It depends on the number of lone pairs on the central atom. A molecule will be nonpolar if there is an equal and opposite pull of electrons. So if the lone pairs are opposite each other and the charges of the bonding atoms cancel each other out, the molecule will be nonpolar, but if not, the molecule will be polar.

SavannahScriven_1F
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Re: Molecular shape and polarity

Postby SavannahScriven_1F » Sun Dec 06, 2020 1:37 pm

This may not exactly answer your question, but I think of it like this: lone pairs on the central atom affect the positions of the bound atoms, which determine the molecule's shape. The shape then determines if the dipoles have the potential to cancel out. If all the dipoles cancel, then the molecule is nonpolar.

Simrah_Ahmed1J
Posts: 88
Joined: Wed Sep 30, 2020 9:49 pm

Re: Molecular shape and polarity

Postby Simrah_Ahmed1J » Sun Dec 06, 2020 1:53 pm

I get your line of thinking and it makes sense, because a lot of nonpolar molecules have no lone pairs on the central atom, those nonpolar molecules are usually in shapes we've learned such as tetrahedral, trigonal planar, trigonal bipyramidal, and octahedral, and usually the atoms bound to the central atom are all the exact same element, which of course cancel out forces and make it nonpolar.
However, its not like there is a strict rule because, for example, take the molecule XeF4. This molecule is in a square planar shape, arranged the way it is shown in the attached image. In this case, all the forces and electron repulsion are evened out and make the molecule nonpolar, even though there are lone pairs on the central atom.
So in general, I think you just have to understand the shapes and you'll be good to go
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IMG_3079.png


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