I read that to compare thermal stabilities of ionic solids:
if the solid has a monoatomic anion, we compare thermal stability on the basis of lattice energy which is inversely proportional to size.
if the solid has a polyatomic anion, we compare thermal stability on the basis of ionic character which can we done using Fajans' Rule.
Could someone please confirm that these are correct?
I have a doubt because I also read from somewhere else that MgCl2 is less thermally stable than BaCl2,
which contradicts the rule as Cl- is monoatomic, Ba2+ is larger in size, so BaCl2 has lesser lattice energy so it should be less thermally stable. So what is the correct answer?