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Emerald Ellspermann 1K
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Postby Emerald Ellspermann 1K » Mon Oct 31, 2016 8:57 am

How do you determine polarity of a molecule? Do you have to draw the molecule according to its shape in order to determine polarity, or is just drawing the lewis structure sufficient to determine the dipole moments and polarity?

Minu Reddy
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Joined: Sat Jul 09, 2016 3:00 am

Re: Polarity

Postby Minu Reddy » Mon Oct 31, 2016 9:38 am

To correctly determine the polarity of a molecule, it is very important to draw the molecule according to its actual shape because attempting to determine the polarity solely by looking at the lewis structure can cause you cancel out dipole moments and get a nonpolar molecule when the molecule is actually polar.

Arie Hakimi 1L
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Re: Polarity

Postby Arie Hakimi 1L » Tue Nov 01, 2016 10:02 pm

You have to draw the VSEPR model and figure out the molecular shape of the molecule. After that, you determine the dipole moments based on the electronegativity of the different atoms (the atom with higher electronegativity pulls electrons towards itself \delta - ). Typically, if there are different kinds of atoms within a molecule, the dipole moments won't cancel out, and the molecule will be polar.

Rana YT 2L
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Joined: Thu Jul 27, 2017 3:01 am

Re: Polarity

Postby Rana YT 2L » Thu Nov 09, 2017 11:55 am

In addition to the posts above, if you would like to get a general sense as to whether a molecule is polar or not, you can also compare the relative electronegativity of each of the atoms that occupy it. If the difference in their electronegativity is great (based on periodic trends), then you can assume that they are polar.

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Re: Polarity

Postby soniatripathy » Thu Nov 09, 2017 12:57 pm

I know that LDMS help a lot especially because polar molecules are not symmetric

Minie 1G
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Joined: Fri Sep 29, 2017 7:04 am

Re: Polarity

Postby Minie 1G » Thu Nov 09, 2017 1:13 pm

You can look for either lone pair electrons or polar bonds.

If we take two molecules, CO2 and H2O which may both seem to be linear in shape because they have 3 atoms each, we find that actually CO2 is linear while H2O is bent. Because the lone pair electrons on water repel the hydrogens and force a bend. CO2, a nonpolar molecule, has two polar C-O bonds BUT they are positioned so that they directly cancel each other out making the whole molecule nonpolar. O=C=O <- the double bonds are directly against each other

This also speaks to symmetry; the symmetric double bonds makes the molecule nonpolar because the charges are more evenly distributed. But the presence of a lone pair electron immediately adds unequal charge distribution, making molecules polar.

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