Electron affinity and acid strength

[Molly Posta 1H]

I'm struggling with the following concept: The greater the electron affinity (and therefore the electronegativity) of A, the stronger is the acid. (Where A is referring to the second element in a binary acid)

Previously, we learned that a shorter, weaker bond corresponds to a stronger acid. By this reasoning, a weaker bond means a weaker acid. In the case of electronegativity/electron affinity, wouldn't A having a high electron affinity make a bond harder to break? How can these 2 concepts of acid strength be applied simultaneously?

[Adrienne Yuh 2B]

Hi! A quick correction: you said "a shorter, weaker bond corresponds to a stronger acid." A LONGER bond would create a weaker bond and therefore a stronger acid, since it can dissociate easily.

For binary acids, a weaker bond comes from the size of the atom (A in the acid). The larger the atom, the larger the radius, making the bond also longer.

Electronegativity only matters in oxoacid and carboxylic acids since it would pull the electrons AWAY from the hydrogen, allowing it to dissociate easily.

[Neha Gupta 2A]

I can totally see where you're coming from. I believe that it's because long bonds are actually weaker, so it's easy for H to be pulled away and contribute to the H3O+ ion in the solution.

[Eric Cruz 2G]

Hi! I struggled with this idea too, but I believe I finally understand. When talking about halogens, bond strength is the focus to understand which acid is stronger. In this case, the greater electronegativity and electronegativity, the stronger the bond. As a result, it is difficult for the H hydrogen to dissociate and bond with h2o to form . There is an inverse relationship: the stronger the bond, the weaker the acid.

However, with respect to oxoacids and carboxylic acids, the focus is on the atoms and their electronegativity and their ability to affect the OH bond. In these cases, the greater the electronegativity of the atom, the more polar the OH becomes (since electrons move towards the electronegative atom) and as a result, the more likely it is for the molecule to donate a proton (strong acid).