What Determines Acid and Base Strength in Bronsted-Lowry Theory?

[Kruz87]

Hello everybody, I'm having difficulty understanding the rationalization behind the strengths of Bronstend Lowry acids and bases and my textbook isn't too helpful. Can someone please expalin to me: (1) What exactly is effective negative charge density? (2) how does electronegativiy correspond to negative charge density? (3) How does negative charge density correspond to the strength or stability of the conjugate base of an acid?

 

[chaoseverlasting]

The total negative charge per unit volume of the atom. The higher the electro negativity, the more charge the atom can retain in a lower volume (the more "pull" it has), and hence higher negative charge density.

If the negative charge density of the conjugate base of an acid is lesser, then that species is more stable as it does not attract the positive charges as strongly. Therefore, it has less tendency to attract the positive species just released by the acid (H+) and the reaction tends more towards the forward side. Ie, H2So4, because SO4(2-) is large in volume (Sulfur and Oxygen are bulky) it has lower negative charge density, and this makes H2SO4 more acidic.

The converse is also true for base strength.