Textbook question 2E.1

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

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Paige Lee 1A
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Joined: Sat Sep 07, 2019 12:16 am

Textbook question 2E.1

Postby Paige Lee 1A » Thu Nov 14, 2019 10:35 pm

For part A, could someone please explain why there must be lone pairs for a 120 degree bond angle?

Kelvin Chung 1C
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Joined: Sat Aug 24, 2019 12:15 am

Re: Textbook question 2E.1

Postby Kelvin Chung 1C » Thu Nov 14, 2019 11:25 pm

The two molecules attached to the central atom are generally more electronegative than the central atom. There must be lone pairs on the molecule with a 120 degree bond angle so that the otherwise linear molecule "bends" downward through electron repulsion with these more electronegative atoms.

Jacey Yang 1F
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Joined: Fri Aug 09, 2019 12:17 am

Re: Textbook question 2E.1

Postby Jacey Yang 1F » Thu Nov 14, 2019 11:32 pm

The lone pair on the central atom has a stronger repelling effect, pushing the bonding pairs closer together to create a bent shape.

Qilan Li 4I
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Joined: Mon Jun 17, 2019 7:23 am

Re: Textbook question 2E.1

Postby Qilan Li 4I » Thu Nov 14, 2019 11:43 pm

Since bond angles are affected by the presence of lone pairs of electrons at the central atom, we can tell if there are lone pairs when a picture only shows bonded pairs/atoms. A lone pair of electrons at the central atom would always repel the shared pair/bonded pair which is why the 120-degree angle would be formed. If there are no lone pairs, the bonded pairs would try to be as far away from each other as possible which would be 180 degrees, and the lone pairs prevent them from doing that (however 180 degrees between bonded pairs can still have lone pairs). Sorry if that was confusing but that is my thought process and I'm not 100% if it's correct.

Paige Lee 1A
Posts: 136
Joined: Sat Sep 07, 2019 12:16 am

Re: Textbook question 2E.1

Postby Paige Lee 1A » Fri Nov 15, 2019 12:14 am

I'm still confused, what about trigonal planar molecules? Don't they have 120 degree bond angles, but no lone pairs?


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