Acidity and Resonance/Delocalization

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Lindsey Chheng 1E
Posts: 110
Joined: Fri Aug 30, 2019 12:16 am

Acidity and Resonance/Delocalization

Postby Lindsey Chheng 1E » Thu Dec 05, 2019 7:29 pm

Can someone please explain how resonance, delocalization, and stabilizing of negative charges contribute to the strength of an acid?

Ryan Narisma 4G
Posts: 104
Joined: Fri Aug 30, 2019 12:18 am

Re: Acidity and Resonance/Delocalization

Postby Ryan Narisma 4G » Thu Dec 05, 2019 8:42 pm

Hi Lindsey Chheng 1H! To answer your question, acids will be strong in either of the two conditions: 1. The length of the H-A bond is longer and can be broken easily or 2. The resulting anion after the acid gives its H+ away is more stable. The first condition is pretty straightforward, Dr. Lavelle gave us the examples of the halogen acids (HF, HCl, HBr, HI). The second condition is kind of tricky and relies on two important factors. For the resulting anion to be stable, the anion must either have resonance OR have a higher electron withdrawing ability (more electronegative atoms to pull on the electrons). When the anion has resonance, it is more stable because of the delocalization of electrons that takes place within the species. When the resulting anion has minimal negative charges, the anion will be more stable. Remember that a greater magnitude of negative charge can be highly reactive, so those species which have minimal negative charges or none at all will be more stable. However, when you are comparing two anions that have the same ionic charge, you have to take a look at the electron withdrawing ability of each species. The species that has a greater number of electronegative atoms will have a higher electron-withdrawing ability to create a more stable anion. I hope this helps!

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