What factors determine the strengths of acids and bases?

Factors that determine the strengths of acids and bases include: electronegativity, resonance, induction, aromaticity, hybridization, and atom size. 

For acids, larger atoms can stabilize negative charge better than smaller atoms, making them weaker acids. For bases, larger atoms can accommodate extra electrons more easily, making them better bases. For electronegativity, if the atom donating a proton (H+) is highly electronegative, it stabilizes the resulting conjugate base (A-) through electron withdrawal, making the acid stronger. Similarly, in bases, if the atom accepting a proton (OH-) is highly electronegative it stabilizes the resulting conjugate acid (H2O), making the base stronger. In acids, resonance stabilization of the conjugate base (A-) increases its stability, making the acid stronger. For aromaticity, in acids if the conjugate base (A-) possesses aromaticity, it is more stable, leading to a stronger acid. Resonance stabilization is more significant than inductive stabilization for stabilizing the conjugate base (A-) of an acid (HA). When the conjugate base (A-) contains an electronegative atom, it enhances the stability of A-, resulting in a stronger acid (HA). Lastly, in acids if the atom donating a proton (H+) has greater s-character in its hybridized orbital, it stabilizes the resulting conjugate base (A-) and makes the acid stronger. If the lone pair of electrons in a base is found in an orbital with more s-character, it will be more stable and less likely to accept a proton.