polar or not polar

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

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Andrea- 3J
Posts: 56
Joined: Tue Nov 14, 2017 3:00 am

polar or not polar

Postby Andrea- 3J » Thu Nov 29, 2018 9:11 pm

On the 6th edition on 4.25 it is asking if CH2Cl2 and SF4 is polar or not polar.
I came across a chart that says tetrahedrals are not polar while pyramidal structures are polar.
CH2Cl2 is a tetrahedral, therefore it is not polar. SF4 is trigonal bipyramidal therefore it is polar.
How would I know whether these structures are polar or not polar without the chart?

Shash Khemka 1K
Posts: 38
Joined: Fri Sep 28, 2018 12:18 am

Re: polar or not polar

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

Carlos De La Torre 2L
Posts: 60
Joined: Tue Oct 09, 2018 12:16 am

Re: polar or not polar

Postby Carlos De La Torre 2L » Thu Nov 29, 2018 10:39 pm

it helps to visualize the molecule in your head, on paper the Lewis model of CH2Cl2 may look symmetrical but in reality, no matter how it is positioned the 2 Cls will be opposite the 2 Hs which explains the polarity, the molecule needs to be symmetrical in 3D in order for it to be non-polar.

Posts: 31
Joined: Fri Sep 28, 2018 12:27 am

Re: polar or not polar

Postby gillianozawa4I » Thu Nov 29, 2018 11:47 pm

In a molecule with one central atom, (a majority of the time ) if the surrounding atoms are different, the molecule is polar. This is because the surrounding atoms have different electronegativity values that do not cancel out. However, I think it's best to draw out the Lewis structure to determine whether a molecule is polar. Hope this helps!

g orloff 1J
Posts: 45
Joined: Fri Sep 28, 2018 12:16 am

Re: polar or not polar

Postby g orloff 1J » Fri Nov 30, 2018 12:28 am

The CCl bonds are slightly more polar than the CH bonds making it slightly more polar. if the molecules are different the molecule is USUALLY polar

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