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Postby 005388369 » Sat Nov 16, 2019 12:00 pm

How do we determine which bonds are polar or not?

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Re: Polarity

Postby WUng_1D » Sat Nov 16, 2019 12:12 pm

If the difference in electronegativity for the atoms in a bond is greater than 0.4, we consider the bond polar. If the difference in electronegativity is less than 0.4, the bond is essentially nonpolar. If there are no polar bonds, the molecule is nonpolar.

When drawing just look for the dipoles and if they cancel eachother out, it will be nonpolar.

Hailey Kim 4G
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Re: Polarity

Postby Hailey Kim 4G » Sat Nov 16, 2019 12:16 pm

An easy way to determine if a molecule is polar or non-polar is to draw the Lewis Structure and see if it is symmetric or non-symmetric. If the Lewis Structure is symmetric, the molecule is non-polar, which also means it only has non-polar bonds. If the Lewis Structure is non-symmetric, the molecule is polar.

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Re: Polarity

Postby lilymayek_1E » Sat Nov 16, 2019 12:20 pm

Polarity in individual bonds is most often determined by the difference in electronegativity between two atoms; typically a difference of 0.5-1.7 between two atoms determines a polar bond. this is the more quantitative way to determine polarity in one bond. you can also look at the periodic table and kinda eyeball it - electronegativity increases as you go to the right across the periodic table, so you can somewhat determine it from that. I feel like most likely on the test, we'll have to determine polarity in a molecule, but what I said about is the general trend of determining polarity in a bond.

Charlene Datu 2E
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Re: Polarity

Postby Charlene Datu 2E » Sat Nov 16, 2019 4:11 pm

Adding onto the structural symmetry, a molecule can be symmetrical but still polar. It depends on where the dipole moments are located.
EX: cis-dichlorethene vs trans-dichlorethene (both are C2H2Cl2)
- in both molecules, the C-Cl bonds have dipole moments
- cis-dichlorethene has both chlorine atoms located on the same side of the molecule, making it a polar molecule. The dipole moments are asymmetrical because the chlorines are both on the same side.
- trans-dichlorethene has the chlorine atoms located on opposing sides of the molecule, cancelling out the dipole moments and making it nonpolar. The dipole moments are symmetrical because the chlorines are evenly distributed.

Aarushi Solanki 4F
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Re: Polarity

Postby Aarushi Solanki 4F » Sat Nov 16, 2019 4:15 pm

A molecule is polar if there are dipoles that don't cancel each other out, making a specific part of the molecule more prone to having a higher electron density (usually near a more electronegative atom). A simpler way to look at this is determining whether the molecule is symmetrical (the element of the atom matters since different elements have different electronegativities) because a symmetrical molecule will have dipoles that cancel each other out.
Last edited by Aarushi Solanki 4F on Sat Nov 16, 2019 4:48 pm, edited 1 time in total.

Anisha Chandra 1K
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Re: Polarity

Postby Anisha Chandra 1K » Sat Nov 16, 2019 4:21 pm

It's important to note that the atoms in a molecule may have large differences in electronegativity, but the molecule itself still isn't polar because the dipole moments cancel. An example of this would be CCl4.

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