why is lithium iodide covalent???

i want to know what is the relation of hydration enthalpy with lattice enthalpy and atomic size????

The large size of iodine exerts a more polarising power to lithium as compared to fluorine and thus has more covalent character than fluorine.Fluorine more over has high electronegativity. So the electro-static force of attraction between Li and F is very high and high enough to hold the two atoms together so firmly