Answer:
Order of decreasing: CaS> LiCl> CsCl. That is CsCl has the lowest lattice energy.
Explanation:
LATTICE ENERGYcan be used to estimate the STRENGHT of the bonds in an ionic compound.
ATOMIC RADIUS is a function of lattice energy. The atomic radius INCREASES as you move DOWN a group. LATTICE ENERGY DECREASES as ATOMIC RADIUS increases.
Considering the cations Lithium +1, and Caesium +1 , as one move DOWN the GROUP the ions get larger, this causes the LATTICE ENERGY TO DECREASE DOWN THE GROUP. This means that between lithium in and caesium ion, the Caesium ion has LOWER LATTICE ENERGY as COMPARE TO LITHIUM ION.
AS ONE MOVE ACROSS THE PERIOD, POSITIVE IONS BECOMES MORE CHARGED, and the MORE THE CHARGE, THE GREATER THE LATTICE ENERGY.
Therefore, Calcium ion will have higher lattice energy than Lithium ion.
