Determining polar and non polar molecules from a lewis structure

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

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abbydouglas1K
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Determining polar and non polar molecules from a lewis structure

Postby abbydouglas1K » Thu Nov 29, 2018 8:10 pm

How do we do determine polar and non polar structures from looking at lewis structures ?

Marcela Udave 1F
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Re: Determining polar and non polar molecules from a lewis structure

Postby Marcela Udave 1F » Thu Nov 29, 2018 8:38 pm

By the electronegativity difference between the atoms. If they cancel each other then it's non polar.

Shash Khemka 1K
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Re: Determining polar and non polar molecules from a lewis structure

Postby Shash Khemka 1K » Thu Nov 29, 2018 9:31 pm

You can usually tell if a molecule is polar or nonpolar based on its Lewis Structure. A good rule of thumb is that a nonpolar molecule will always be symmetrical and its dipole movements will cancel out (neutral charge). Polar molecules are not symmetrical and their dipole movements will result in an unequal pull. An example of a nonpolar molecule is CH4. Its dipole movements cancel out and its shape is tetrahedral (symmetrical). An example of a polar molecule is H2O. Its dipole movements push towards Oxygen and the shape is bent (not symmetrical). CH2Cl2 is a polar molecule due to the fact that its dipole movements do not cancel out. SF4 is polar due to the lone pair on the S providing an unequal repulsion.

Anjali_Kumar1F
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Re: Determining polar and non polar molecules from a lewis structure

Postby Anjali_Kumar1F » Thu Nov 29, 2018 9:53 pm

How do you know HCN is polar or non polar?

Anmol_cheema_2F
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Re: Determining polar and non polar molecules from a lewis structure

Postby Anmol_cheema_2F » Thu Nov 29, 2018 10:33 pm

You can usually tell from a lewis structure is a molecule is polar by seeing if they're dipole moments cancel out, which usually happens based off their symmetry.

Cameron_Greenberg_3C
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Re: Determining polar and non polar molecules from a lewis structure

Postby Cameron_Greenberg_3C » Fri Dec 07, 2018 4:52 pm

Anjali_Kumar3E wrote:How do you know HCN is polar or non polar?


HCN is polar. Although the molecule is linear, the electronegativity difference makes the hydrogen side slightly positive and the nitrogen side slightly negative.

Rosha Mamita 2H
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Re: Determining polar and non polar molecules from a lewis structure

Postby Rosha Mamita 2H » Fri Dec 07, 2018 6:01 pm

This is determined by the symmetry of the molecules and that symmetrical molecules would have dipole moments cancelling each other out. Though often, molecules with lone pairs tend to be polar because the pair’s dipole moment does not cancel out, however there are exceptions to this such as how square planar is non polar and has two lone pairs.

Ryan Danis 1J
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Re: Determining polar and non polar molecules from a lewis structure

Postby Ryan Danis 1J » Fri Dec 07, 2018 8:09 pm

If the dipole moments cancel out, the molecule is non polar.

Ivan Tadeja 4B
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Re: Determining polar and non polar molecules from a lewis structure

Postby Ivan Tadeja 4B » Fri Dec 07, 2018 8:18 pm

Anjali_Kumar3E wrote:How do you know HCN is polar or non polar?


There is a negative charge on the N and a positive charge on the H. When drawing the lewis structure, you notice that the CN bond is a triple bond with a lone pair while the HC bond is only a single bond. Thus, the dipole moments do not cancel which makes the compound polar.


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