Homework 3F3

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Jasmine 2C
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Homework 3F3

Postby Jasmine 2C » Thu Nov 21, 2019 12:33 am

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.

Zaynab Hashm 2I
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Re: Homework 3F3

Postby Zaynab Hashm 2I » Thu Nov 21, 2019 12:37 am

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!

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Re: Homework 3F3

Postby AlyshaP_2B » Thu Nov 21, 2019 1:04 am

Any time the central atom is surrounded by two or more different atoms in a tetrahedral, there will be dipole dipole forces.

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Re: Homework 3F3

Postby sarahsalama2E » Thu Nov 21, 2019 9:57 am

Would CH2I2 be polar or nonpolar? if the picture in the problem has the I opposite from one another.

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Re: Homework 3F3

Postby AGulati_4A » Thu Nov 21, 2019 10:10 am

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.

Audrie Chan-3B
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Re: Homework 3F3

Postby Audrie Chan-3B » Thu Nov 21, 2019 12:10 pm

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.

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