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MIDTERM Bond Length Question

Posted: Wed Nov 07, 2018 7:03 pm
by Annalyn Diaz 1J
There was a question on the midterm about determining the bond length for N-O in NO2, given that the a single bond is 140Å(?) and a double bond is 120Å(?) (I don’t quite remember the units). Any clue on how to determine that?

Re: MIDTERM Bond Length Question

Posted: Wed Nov 07, 2018 8:07 pm
by bonnie_schmitz_1F
I believe that the Lewis structure for NO2 has one single bond and one double bond. So, in nature, this double bond would be evenly distributed between the two, so I assumed the each bond would be approximately a "1.5" bond. Using this logic, I guessed that the bond length would be about 130A.

Re: MIDTERM Bond Length Question

Posted: Thu Nov 08, 2018 1:32 am
by MadisonB
The experimentally determined bond lengths of all the bonds are the same. Bonds lengths are the average of all of the resonance structures. I also got 130.

Re: MIDTERM Bond Length Question

Posted: Thu Nov 08, 2018 2:51 am
by Esha Harwalkar 3F
For the question that came this one, did people say that the bond length was the same for all the structures since they are resonance structures? (the bond lengths for the most stable structure of the compound?)

Re: MIDTERM Bond Length Question

Posted: Thu Nov 08, 2018 11:24 am
by Krista Mercado 1B
Since a resonance hybrid is a blend of Lewis structures, all the bond lengths are the same. Thus, even though there are both single and double bonds in the resonance structure, all of the bond lengths will be the average between the different bond lengths of the structure. For this specific question, this would be 130.

Re: MIDTERM Bond Length Question

Posted: Thu Nov 08, 2018 11:29 am
by shaunajava2e
since there was only the two bonds, the length would be the average of their individual lengths, so the average of 140 and 120, resulting in 130

Re: MIDTERM Bond Length Question

Posted: Thu Nov 08, 2018 2:41 pm
by Sam Kelly 1K
During lecture Lavelle gave us the experimental value for the average bond length in Nitrate, which turned out to be 1.24 A, maybe because when you draw the three possible structures for NO3-, there are two single bonds and one double bond. That being said, I think the correct answer on the midterm was 130 A.

Re: MIDTERM Bond Length Question

Posted: Thu Nov 08, 2018 5:40 pm
by Bruce Chen 2H
To be honest, I just took the averages of the two lengths as the structures need to be balanced, so it was 130.

Re: MIDTERM Bond Length Question

Posted: Fri Nov 09, 2018 1:55 am
by Dayna Pham 1I
I assumed that both the bond-lengths were the same, that they were each single-double bond hybrids.
Therefore, I thought it was 130.

Re: MIDTERM Bond Length Question

Posted: Fri Nov 09, 2018 9:41 am
by Julia Jones 1G
In discussion, our TA said they would be accepting any answer in between 120 and 140.

Re: MIDTERM Bond Length Question

Posted: Fri Nov 09, 2018 9:45 am
by Nicholas Le 4H
Since they actually exist as a hybridization resonance structure, the true bond lengths exist between 120 and 140. We need further experimental data to get a more accurate answer of the true bond length.

Re: MIDTERM Bond Length Question

Posted: Fri Nov 09, 2018 10:48 am
by Yiwen Chen-3G
I got 130 cuz there are 2 resonance structures.

Re: MIDTERM Bond Length Question

Posted: Fri Nov 09, 2018 10:10 pm
by Riley Dean 2D
does anyone happen to know why it averages out so they're all the same length as opposed to just letting the double bond be a different strength than the single bond?

Re: MIDTERM Bond Length Question

Posted: Fri Nov 09, 2018 10:19 pm
by Sapna Ramappa 1J
Due to resonance blending, the bond length will be 130 pm (or really any value in between 120pm and 140pm)!

Re: MIDTERM Bond Length Question

Posted: Sat Nov 10, 2018 2:03 pm
by Porus_Karwa_2E
I got 130 pm because I took the average of the 140pm and 120pm.

Re: MIDTERM Bond Length Question

Posted: Sat Nov 10, 2018 2:44 pm
by Maya_Peterson1C
There were resonance structures for the molecule that included single and double bonds, so the actual molecule would have an average of those two bonds. I took the average of the two lengths and got 130pm.