We have seen before that because similar functional groups react in similar ways that compounds with similar functional groups will have similar pK a values. We can use this fact as a basis to predict trends in acidity or basicity. Recall that the role of a base is to share an electron pair with a proton, resulting in a new bond to that proton. A molecule that can donate electrons more readily will therefore be a stronger base. Because we know that stronger bases have weaker conjugate acids , we can apply this same analysis to determine acidity as well.
Many factors can influence a molecule's ability to donate electrons.
The most common factors are electronegativity, resonance, and the inductive effect . We consider each of these below. Recall that electronegativity is the measure of an atom's attraction for electrons. The higher the electronegativity, the greater the attraction. We can extend this idea further and conclude that atoms with higher electronegativity will be less inclined to share their electrons with a proton.