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Homework 3F3

Posted: Thu Nov 21, 2019 12:33 am
by Jasmine 2C
For which of the following molecules will dipole–dipole interactions be important: (a) CH4; (b) CH3Cl; (c) CH2Cl2; (d) CHCl3; (e) CCl4?
Why does the lewis structure for (b) have the two chlorines at a corner and not opposite each other? Shouldn't they be opposite each other so there's less energy repulsion between their lone pairs? And if they are opposite each other, their dipole moments would cancel and not be considered polar, so then dipole-dipole interactions won't be important.

Re: Homework 3F3

Posted: Thu Nov 21, 2019 12:37 am
by Zaynab Hashm 2I
even if you put them opposite to each other, remember that tetrahedral structures have bond angle 109.5 degrees, and so they won't even be in complete symmetry to cancel the dipole moments

here's a tip; all carbon atom tetrahedral structures are polar, unless the carbon atom is surrounded by 4 atoms of the same element, then it would be non polar

hope that helps!

Re: Homework 3F3

Posted: Thu Nov 21, 2019 1:04 am
by AlyshaP_2B
Any time the central atom is surrounded by two or more different atoms in a tetrahedral, there will be dipole dipole forces.

Re: Homework 3F3

Posted: Thu Nov 21, 2019 9:57 am
by sarahsalama2E
Would CH2I2 be polar or nonpolar? if the picture in the problem has the I opposite from one another.

Re: Homework 3F3

Posted: Thu Nov 21, 2019 10:10 am
by AGulati_4A
I think you mean for c) and yeah I thought they should be that way I think in this case they want you to assume the most unstable resonance structure. But you shouldn't worry about this, you won't encounter questions like this on the test -- and if you do, they probably will give you the lewis structure.

Re: Homework 3F3

Posted: Thu Nov 21, 2019 12:10 pm
by Audrie Chan-3B
The placement of the chlorines in the lewis structure does not matter. If you picture the VSEPR structure for it, you will notice that the chlorines are not symmetric/ 180 degrees from each other, so they cannot cancel out.