* Ionic Size: Chloride ions (Cl-) are smaller than bromide ions (Br-).

* Electrostatic Attraction: Smaller ions allow for a closer proximity between the positively charged silver ions (Ag+) and the negatively charged halide ions (Cl- or Br-). This closer proximity leads to stronger electrostatic attractions.

* Lattice Energy: Lattice energy is a measure of the strength of the electrostatic interactions within a crystal lattice. Stronger attractions result in higher lattice energy.

In summary: Because the chloride ion is smaller than the bromide ion, the Ag+ and Cl- ions can get closer together, leading to stronger electrostatic attractions and a higher lattice energy in AgCl.