Resonance

[kellyz_1C]

How can you tell when a molecule has resonant structures? Also, the book mentions how resonance lowers the energy of a molecule (along with delocalization) and I am a bit confused on how that is possible.

[Isabelle De Rego 1A]

you can tell when a molecule has resonance usually when it has a double or triple bond. If you remember, there can be several resonance structures for one molecule, so it all depends on the placement of the bond. Also, resonance structures are in a lower energy state for the molecule. There is usually a way to give a molecule a full octet and what not, but the optimum state for that molecule is when it has a lower formal charge, which is the resonance structure. There is probably a more technical explanation for this, but that's the basic concept.

[Nina_A_Section1E]

A molecule can have a resonance structure when certain bond(s), usually a double or triple bond, can be placed in multiple locations around the central atom without changing the overall formal charges.
It goes into more depth here! https://socratic.org/questions/how-can- ... tructure-1

[Elizabeth Parker 1K]

Can someone please explain delocalization?

[Jacy Black 1C]

For a resonance structure with one double bond and two single bonds, would the bond length of all of them become a hybrid of all three bonds? I know all the bonds included would have partial double bond character. Affecting the length, would the double bond become a bit longer than normal, and would the single bonds become a little shorter than normal?

[JoeyAnn Mateo 1D]

Delocalization means that a shared electron pair is distributed over several pairs of atoms and cannot be identified with just one pair of atoms.
This is from the book, page 81

[Shione Nakahara 1F]

Delocalization is when electric charge is spread over more than one atom. If there are delocalized electrons, it increases the stability of the system compared to a similar system where electrons are localized.

[Isobel Tweedt 1E]

Also remember to address how bond strength is affected by resonance structures. For instance a double bond in a resonance structure is shorter (and thus stronger) than a regular double bond. This is because the actual structure is a combination of the resonance structures (and thus bonds).