Double Bond vs Single Bond Length

[Tracey Tran 3I]

Are double bonds shorter than single bonds because they're stronger? If so, then why is the observed N-O bond length in the NO3- 1.24 A.

[VPatankar_2L]

The length of the bonds is in part based on the distance between two atoms. Atoms that form double bonds with one another have a stinger attraction between them which means they are pulled closer together than if they were connected by a single bond. Thus, the distance between them is smaller which means that double bonds are shorter than single bonds.

[Montana James 4G]

to add on, I think Dr Lavelle said that in actual experimental data, all the bond lengths are the same (1.24A). So the Lewis structure is just a model.

[Kishan Shah 2G]

Correct, the lewis structure is just a rough model and Dr. Lavelle did say that the actual length is 1.24 angstrom. The double bonds and triple bonds contain more electrons, thereby exerting a stronger force on the nuclei of the atoms and this pulls the atoms closer together hence shorter bond lengths.

[Arvind 4G]

In general, yes. The NO3 is a special case of resonance as its double bond is not on one of the bonds, but rather each bond is a bit stronger than a single bond and a bit weaker than a double bond.

[TheresaDsilva4A]

I spoke with an LA after class about this specific topic. He explained that the electrons of the NO3- ion are evenly distributed amongst the three bonds. Thus, in reality, there is no distinguishable difference between the double/single bonds. This is the reasoning behind the experimental 1.24-angstrom value that Dr. Lavelle provided. I hope this add-on helps :)

[Sarah Zhari 1D]

Additionally, in resonance structures, the bond lengths are equal due to the delocalization of electrons between the atoms. The molecule, as a result, has a lower energy, and this helps to stabilize the molecule.