How does the size of an ion affect the hydration radii?1 AnswerRupal Dasgupta, A learner.1.7k ViewsIn a group, ionic radius increases from top to bottom and the hydrated radius decreases  from top to bottom. 

Hydration energy is the amount of energy liberated when an ion gets hydrated that is , it accepts water molecule. e.g. lithium ion is small in size so it accepts large number of water molecule so it's hydration energy is more whereas caesium ion is bigger in size so it accepts less number of water molecule and has less hydration energy. 

Li+ <Na+ <K+ < Rb+ <Cs+ (ionic radius)

Li+(aq) > Na+(aq) > K+(aq) > Rb+(aq) > Cs+(aq) ( hydrated radius)