Bond Lengths

Anand Narayan 1G
Posts: 61
Joined: Fri Sep 28, 2018 12:15 am

Bond Lengths

When there are double bonds in a structure, for example the Nitrate ion, NO3 2-, and chemists observe the actual N-O bond length, is every bond length the same length, despite the fact that we draw it with one double bond and two single bonds indicating that they are different lengths?

Elias Omar 1G
Posts: 52
Joined: Fri Sep 28, 2018 12:17 am

Re: Bond Lengths

NO3 2- has resonance, meaning that the double bond in it can be between any of the three oxygens and the nitrogen atom. It has been experimentally determined for the N-O bonds in NO3 for example that they are all 124 pm, in between the single bond length of 140 pm and the double bond length of 120 pm. This idea applies to all resonance structures.

Posts: 62
Joined: Fri Sep 28, 2018 12:15 am

Re: Bond Lengths

The bond lengths are equal despite that double and single bonds have different lengths. Somehow the actual bond length will fall between the length of single or double if those are the only bonds present.

Posts: 30
Joined: Fri Sep 28, 2018 12:27 am

Re: Bond Lengths

What does it mean for the bong length to be 120 pm and 140pm, or 124 pm like you said? I really had trouble with that question.

Nicolette_Canlian_2L
Posts: 77
Joined: Fri Sep 28, 2018 12:25 am
Been upvoted: 1 time

Re: Bond Lengths

I don't understand where the 124 is coming from. Is there a calculation that needs to be done to come to this bond length value?

KHuang1L
Posts: 60
Joined: Fri Sep 28, 2018 12:19 am

Re: Bond Lengths

The bond length for each N-O bond is an average of the bond lengths for all three resonance hybrids.

kamalkolluri
Posts: 65
Joined: Fri Sep 28, 2018 12:17 am
Been upvoted: 1 time

Re: Bond Lengths

so NO3- is a resonance hybrid so the electrons in the double bonds can exist anywhere. This causes the bond length of N-O to be an average of the NO double and single bonds. The overall bond lengths are all the same

Ashley P 4I
Posts: 64
Joined: Wed Nov 15, 2017 3:04 am

Re: Bond Lengths

There was a question like this on the midterm and I'm still lost on how to do it. Can someone please explain how to even calculate bond lengths? Is there like a number we need to attribute to double and single bonds thats universal?