2E.25

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

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Jessica Luong 3E
Posts: 42
Joined: Sat Aug 17, 2019 12:17 am

2E.25

Postby Jessica Luong 3E » Sun Nov 24, 2019 11:17 pm

Draw the Lewis structure and predict whether each of the following molecules is polar or nonpolar: (a) CH2Cl2; (b) CCl4; (c) CS2; (d) SF4.

MAC 4G
Posts: 121
Joined: Wed Sep 18, 2019 12:16 am

Re: 2E.25

Postby MAC 4G » Mon Nov 25, 2019 1:36 pm

1) Draw the Lewis structures of the molecules
2) Determine which bonds have the greatest difference in electronegativity (for example, C-Cl has a greater difference than C-H)
3) Draw the dipole moments for those bonds of greatest electronegativity difference.
4)Compare the directions of the dipole moments- if they cancel, it is nonpolar; if they do not cancel, it is polar.

You also have to think about the shape of the molecule. For example, in part (a) (CH2Cl2), the molecule has a tetrahedral shape, so the dipole moments do not cancel, even though they look they could in the Lewis structure so it's polar.

Chris Tai 1B
Posts: 102
Joined: Sat Aug 24, 2019 12:16 am

Re: 2E.25

Postby Chris Tai 1B » Wed Nov 27, 2019 7:05 pm

Be careful when determining whether a molecule is polar or nonpolar - it matters if the dipole moments cancel or not. The bonds within a molecule may be polar, but the molecule as a whole may be nonpolar if those polar dipole moments cancel. For instance, in CCl4, the dipole moments all cancel since there's an even distribution of polarity around the carbon atom, all the chlorine atoms are equally electronegative.
If a molecule is linear, then it is polar if there is a significant difference in electronegativity between the two atoms in the molecule and nonpolar vice versa. However, if a molecule is polyatomic, then one must also consider the rest of the atoms and the shape of the molecule and see if the dipole moments cancel.


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