Final answer:
LiF is expected to have the largest lattice energy due to its smaller ion size and the strong attractions between Li+ and F- ions. It outcompetes the other options because highly charged and small ions create stronger electrostatic forces, leading to higher lattice energy.
Step-by-step explanation:
The lattice energy of an ionic compound is influenced by the charges of the ions and their sizes. Looking at the given options, we consider both the charge magnitude and size of the ions involved. A higher charge and a smaller ion size result in a larger lattice energy because the ions can get closer together and the electrostatic forces between them are stronger.
LiF has a smaller cation (Li+) and a highly electronegative anion (F-) as compared to the other options. Due to smaller ion size and stronger ionic attractions, LiF would have the highest lattice energy among the given choices. Lattice energies tend to be higher for compounds with smaller and more highly charged ions, so a compound like LiF fits this description.
Moving down the group on the periodic table, elements have larger atomic radii. Therefore, KF, KI, NaF, and LiI would have lower lattice energies compared to LiF since potassium and sodium have larger atomic radii than lithium, and iodine has a larger atomic radius than fluorine. It's the combination of the small lithium ion and the small fluorine ion in LiF that results in the largest lattice energy among the options given.