Polar vs. Nonpolar

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

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Mallika Chimpiri 3K
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Polar vs. Nonpolar

Postby Mallika Chimpiri 3K » Wed Nov 13, 2019 7:07 pm

Can someone explain how to determine if a molecule is polar or non polar by looking at its molecular geometry/shape?

Victoria Zheng--2F
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Joined: Fri Aug 09, 2019 12:17 am

Re: Polar vs. Nonpolar

Postby Victoria Zheng--2F » Wed Nov 13, 2019 7:12 pm

To determine if the molecule is polar or nonpolar, you would draw the dipole moments for the molecule to see if they cancel out. If the dipole moments cancel out, then the molecule is nonpolar. If the dipole moments do not cancel out, then the molecule is polar.

BNgo_2L
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Re: Polar vs. Nonpolar

Postby BNgo_2L » Wed Nov 13, 2019 7:13 pm

A molecule is polar when then there is a clear dipole moment, meaning there is one end that is distinctly partially negative and the other end that is distinctly partially positive. A molecule is nonpolar when there is no dipole moment or when the dipole moments cancel each other out by the same partial charge going in opposite directions or by going towards each other.

ishaa Diwakar 4E
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Re: Polar vs. Nonpolar

Postby ishaa Diwakar 4E » Wed Nov 13, 2019 9:56 pm

Also, often molecules with different electron domain and VSEPR geometries will be polar, since a lone pair will be in place of the ED and will prevent the dipoles from cancelling. An example of this is PF3.

RRahimtoola1I
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Re: Polar vs. Nonpolar

Postby RRahimtoola1I » Sat Nov 16, 2019 3:26 pm

It's better to determine whether a molecule is polar or non polar based on VSPER rather than Lewis Structure because it isn't always clear with the Lewis Structure. For H2O for example it seems like it would be non polar because it's symmetrical but the VSPER structure shows it's polar because of the lone pair.

PGao_1B
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Re: Polar vs. Nonpolar

Postby PGao_1B » Sat Nov 16, 2019 4:40 pm

It is generally not recommended to look at a molecule's geometry / shape when determining if it's polar or non polar. It is best to use the VSEPR model and calculate the actual dipole moments to see if they add up to a net value of 0. If they do, the molecule is non polar, and if they do not, the molecule is polar.

Jacob Motawakel
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Re: Polar vs. Nonpolar

Postby Jacob Motawakel » Sat Nov 16, 2019 4:50 pm

In a polar molecule, there is a distinct dipole moment, and in a nonpolar molecule, there is no dipole moment because they cancel out.

Jingyao Chen 4H
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Joined: Fri Sep 27, 2019 12:19 am

Re: Polar vs. Nonpolar

Postby Jingyao Chen 4H » Sat Nov 16, 2019 4:55 pm

A thing to remember is that there are polarity between bonds, and there’s also polarity of the overall molecule. Bonds could be polar, but in certain cases, because the molecule is symmetric, the overall molecule is not polar. Symmetry and the overall 3D shape is the thing that you should base off polarity on.

Eva Zhao 4I
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Re: Polar vs. Nonpolar

Postby Eva Zhao 4I » Sat Nov 16, 2019 7:50 pm

While not always the case, symmetrical shapes typically indicate the molecule is nonpolar; there are dipole-dipole interactions, but they cancel out for a nonpolar molecule. Asymmetrical shapes typically indicate the molecular is polar since the dipole-dipole interactions can't cancel out.

Nicholas_Gladkov_2J
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Re: Polar vs. Nonpolar

Postby Nicholas_Gladkov_2J » Sat Nov 16, 2019 9:40 pm

Mallika Chimpiri 3K wrote:Can someone explain how to determine if a molecule is polar or non polar by looking at its molecular geometry/shape?


By looking at the shape of the molecule, yes, most likely you can determine the polarity of that molecule. If the shape is linear, tetrahedral, and octahedral most likely the shape will be non-polar, only if the surrounding atoms are all the same. If there is an atom with a greater electronegativity, however, the molecule will be polar.

Megan Cao 1I
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Joined: Sat Sep 07, 2019 12:18 am

Re: Polar vs. Nonpolar

Postby Megan Cao 1I » Sat Nov 16, 2019 9:46 pm

generally, if the molecule has no lone pairs it should be nonpolar. the only cases where the molecule has no lone pairs and is polar is when the surrounding elements of the central atom are not the same (CCl4 v CCl3F). Also if there are lone pairs involved, but they can cancel it's polarity, the molecule should be non polar.

(generally) Shapes and whether they're polar or not (central atom is surrounded by the same kind of atom (ex:CH4)):
nonpolar: linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral, square planar
polar: bent/angular, trigonal pyramidal, seesaw, t-shape, square pyramid

stephaniekim2K
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Re: Polar vs. Nonpolar

Postby stephaniekim2K » Sat Nov 16, 2019 10:02 pm

You need to draw the lewis structure and it helps to draw arrows to the negative charged atom from the positively charged ion. If there are two different poles, then the molecule is polar, if both cancel out, it is nonpolar.

ThomasNguyen_Dis1H
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Joined: Fri Aug 30, 2019 12:17 am

Re: Polar vs. Nonpolar

Postby ThomasNguyen_Dis1H » Sat Nov 16, 2019 10:04 pm

First look at the molecular geometry that is 3D and draw dipole moments to see if they cancel out. You have to keep in mind that the geometry is 3 dimensional and take it into account when seeing if the dipoles cancel out.


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