Bond Lengths

[gabbym]

How can you determine if all the bond lengths are the same based off of a Lewis Structure?

[Elena Maneffa 1E]

Usually, in a bond length, specific bond lengths will be given to you. For example, let's say you are given that a C=0 bond is a given length, x. If you see that in your lewis structure you have in total three bonds and each of these 3 bonds are a C=0 (C double bonded to an 0), then you know all the bond lengths are the same and each of the bond lengths are equal to this given length, x.

[Ashley Zhu 1A]

Also, if you see that your Lewis structure is going to have resonance structures, then you know that all of the bonds involved will have the same length.

[705088777]

Is it because the bonds average out and almost move around?

[AdityaGuru1H]

Basically, with resonance structure the resonance bonds are basically a blend of the possible bonds since the electrons are more free to move around between the bonds and so due to some interaction that we don't really need to know too much about they will be something a little bit below the average of all the bonds.

[Danielle_Gallandt3I]

For resonance structures it also depends on which structures are contributing more to the overall resonance structure. So if the structures with double bonds have lower energy than the structures with single bonds, they will be contributing more to the overall structure, so the bond length is probably going to be closer to the length of a double bond than it is to the length of a single bond.