polar vs non polar

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

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polar vs non polar

Postby JustinHorriat_4f » Sun Nov 17, 2019 11:37 pm

Can we distinguish a polar molecule between a non polar molecules by just looking at the bonds inside the molecule and see if the there is dipole moments and if they cancel out, or can we just have to know right away by how the structure is drawn?

Marty Hockey
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Re: polar vs non polar

Postby Marty Hockey » Mon Nov 18, 2019 12:01 am

Often times you can determine if the molecule is polar or non-polar by examining the symmetry of the molecule to see if they cancel out. If it is not apparent that they cancel out through symmetry calculations should ensue.

Eva Zhao 4I
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Re: polar vs non polar

Postby Eva Zhao 4I » Fri Nov 22, 2019 12:40 pm

To add on, sometimes you can tell just by looking at the formula where it may be obvious that hydrogen bonds are present, etc. Often times, it's better to draw out the structure to be sure, during which looking at the symmetry of the structure helps to determine whether or not it's polar/nonpolar. Nonpolar molecules are symmetrical, and polar molecules are typically asymmetrical.

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Re: polar vs non polar

Postby nehashetty_2G » Fri Nov 22, 2019 12:54 pm

I personally always draw out the formula (unless it's a common compound that I know is non polar or polar like CH4 or H2O respectively). The reason is that a lot of times there are lone pairs that are not reflected in the compound's formula that are discovered only after drawing the structure. For example, in BrF5, one would think that the dipoles cancel out since all the bonds are between Br and F making it nonpolar, but since there is actually one lone pair, the molecule is actually polar.

Sanjana Munagala_1j
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Re: polar vs non polar

Postby Sanjana Munagala_1j » Fri Nov 22, 2019 6:17 pm

You should also take into consideration the VSEPR shapes. For example, if you have a tetrahedral, CH4, you know it is a nonpolar molecule because of symmetry. However, if you had H2Cl2C, you might draw a lewis structure where the two chlorine atoms are opposite from each other and the same for the hydrogen and assume that it is a nonpolar molecule. However, this is not the case, because in 3D the dipoles don't actually cancel out.

Hope that helps!

Victoria Otuya 4F
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Re: polar vs non polar

Postby Victoria Otuya 4F » Fri Nov 22, 2019 6:34 pm

Does a non-polar molecule mean it has a Dipole-Dipole intermolecular force?

Emma Popescu 1L
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Re: polar vs non polar

Postby Emma Popescu 1L » Fri Nov 22, 2019 7:56 pm

Victoria Otuya 4F wrote:Does a non-polar molecule mean it has a Dipole-Dipole intermolecular force?

A polar molecule has dipole-dipole interactions. A non-polar molecule has London dispersion interactions (induced-dipole induced-dipole)

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