Two separate series of chloride salts are considered at 298 K.
Series A (constant radius, variable charge):
• NaCl, MgCl₂, AlCl₃ (all cations have radii ≈ 72 pm)
Series B (constant charge, variable radius):
• LiCl, NaCl, KCl (cation radii: Li⁺ 76 pm, Na⁺ 102 pm, K⁺ 138 pm)
Assume that the chloride anion radius is 181 pm in all cases.
(a) Predict the relative magnitudes of the lattice energies for the salts in Series A, listing them from most exothermic to least exothermic. Provide a concise explanation.
(b) Predict the analogous order for the salts in Series B and explain your reasoning.
(c) Compare and contrast the trends observed in Series A and Series B, focusing on how variations in ionic charge versus ionic size affect lattice energy.