This fact is caused by the high (in modulus) hydratation enthalpy of Litium (-519 kJ/mol) compared to the other Alkali Metals (Na -406 kJ/mol, K -322 kJ/mol, Rb -300 kJ/mol, Cs -264 kJ/mol), that's why the Litium cation creates more and more stable bonds with water molecules causing its hydratated from to be larger than the other ones.

What you are saying is that Li has more number of water molecules associated with it (around it) in the hydrated form, that's OK.

Yet, if you consider ions larger than Li like :

or

or

or

,

These ions are already large. So, putting some water molecules (even if less in number) around these ions will only increase the size to a greater extent right?

How does having many water molecules around Li and having lesser number of water molecules around , say K, change the sizes of the respective ions.

I mean like there are already spheres and you are just adding stuff on the spheres. The radii of the spheres must increase by a certain amount.

The initially larger one will end up getting a larger radius finally. Although the radius of the smaller one has also increased, how can it become larger than the other finally?

To put it mathematically:

Let us say the radius of

is

.

Let us say the radius of

is

.

Obviously,

.

Now,

Let us say we add radius

to

(during hydration).

Let us say we add radius

to

. (during hydration).

Well, according to the facts,

.

But how?? Why is this

I know what I have written is confusing, but that is the state of confusion I am in.

Pl. help me out.