Hi! I have to design an experiment for my chemistry class. I was wondering why MgCl2 and CaCl2 are exothermic when dissolved in water, while NaCl and KCl are endothermic when dissolved in water. Is this something to do with the number of valence electrons on the cation, since Mg and Cl both are in the second column of the periodic table while Na and K are both in the first column? Thank you!