Stability of Anions Considering Strengths of ACids

[Ayesha Aslam-Mir 3C]

When characterizing the strengths of acids, one aspect to consider is resonance. I think this has something to do wih the stability of an anion and delocalizing the negative charges.

How do we determine the stability of an anion and how does that correspond with the strength of an acid? How does resonance inform the stability of an anion?

[Jeffrey Doeve 2I]

So we know the stability of the anion is crucial to determining the strength of an acid. Think of it this way: If the anion is more stable, the acid will want to dissociate more and lose its proton to form the stable anion. Resonance structures just happen to be one indication of a stable anion, as the electron is delocalized and able to help fill other atoms' octets. This means they are less likely to react and more stable. Another way to determine stability would be the delocalization of charge, which would spread the energy over the entire atom and result in more stability. As a result, things with a means of stable anions will form strong acids.

[anikamenon2H]

The more stable the resulting anion is, the more likely it is to form and for it to form, the acid must give up the proton or H+. This is why resonance relates to the strength of the acid because resonance makes the anion more stable. Anions can also be stabilized through electron withdrawing atoms, which is just another way of saying atoms with higher electronegativity. Because these atoms have higher electronegativity, they delocalize the negative charge of the anion better, which makes it more stable and thus makes a stronger acid. Some examples of these atoms include Cl, Br, F and I.

Hope this helps!

[Nhu Pham-Dis3G]

To determine the stability of an anion you should determine the hybridization of the atom that bears the charge. The greater the s-character of this atom is, the more stable the anion is.

[CesarLec1]

If an anion is delocalized it is more stable. Think of it like its spreading across the whole molecule and if it is delocalized more, then it isn't just concentrated in one area. Thus, when it is more stable, the molecule will be more inclined to let go of the proton because it wont upset the balance it has going on.