2E.5

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Alex Tchekanov Dis 2k
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Joined: Sat Aug 24, 2019 12:16 am

2E.5

Postby Alex Tchekanov Dis 2k » Fri Nov 15, 2019 3:02 pm

In the homework, it asks what is the expected bond length in ClO2+
I thought that since it is a bent molecule with one lone pair that the answer would be less than 180 degrees because it is less than linear, and also in the example of H20, the angle is 120 degree and H2O has two lone pairs so, therefore, I thought it would be in between 180 and 120 degrees, however the answer in the textbook says it is less than 120 degrees.
Can someone please explain why

MingdaH 3B
Posts: 133
Joined: Thu Jul 11, 2019 12:17 am

Re: 2E.5

Postby MingdaH 3B » Fri Nov 15, 2019 3:07 pm

ClO2+ has a trigonal planar geometry while H2O has a tetrahedral geometry. The bond angle should be 120 degrees for ClO2, but the lone pair makes it slightly under 120 degrees. the bent shape of H2O is different due to the added lone pair that creates the tetrahedral geometry when counting lone pairs

Sebastian Lee 1L
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Re: 2E.5

Postby Sebastian Lee 1L » Fri Nov 15, 2019 3:13 pm

Ok, so like you figure out, ClO2- has a lewis structure where a central chlorine is double bonded to oxygen atoms with a lone pair on the chlorine. Here we have 3 regions of electron density (2 bonding regions and one lone pair). A molecule with 3 regions of electron density will be based off the trigonal planar shape. However, since we have one lone pair, only two bonded atoms are present, which creates the bent shape as you stated.

However, where I think you got confused is that in this bent structure, we base it off the trigonal planar shape (3 regions). The trigonal planar shape will have bond angles of 120 degrees. If you replace one atom in trigonal planar with a lone pair, you can still think of the lone pair as a more repulsive atom. So if you had a bonded atom that repelled other atoms to 120 degrees, a lone pair will repel the other atoms even more. Therefore, the bond angle in ClO2- will be even less than the 120 degrees characteristic of trigonal planar. (Bent isn't based off linear where there are only 2 regions of e- density).

Sebastian Lee 1L
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Joined: Fri Aug 09, 2019 12:15 am
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Re: 2E.5

Postby Sebastian Lee 1L » Fri Nov 15, 2019 3:16 pm

Also to address your comment on H2O:
H20 is based off the tetrahedral shape since it has 2 bonding pairs and 2 lone pairs (4 total regions of electron density). In a tetrahedral molecule, the angles are 109.5 degrees. When you replace two atoms for two lone pairs, this angle will be similar but actually less since lone pairs will repel and push away the other bonded atoms. These bonded atoms will come closer to each other which explains why the bond angle for H2O is actually 104.5 degrees.


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