Hydration Energy Order of Alkali Metals

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The hydration energy order of alkali metal cations is established as Cs+ > Rb+ > K+ > Na+ > Li+. This order contradicts the expectation based on ionic radius, as cesium (Cs+) has the largest radius yet exhibits the highest hydration energy. Hydration enthalpies are negative, with Cs+ at -264 kJ/mol and Li+ at -520 kJ/mol, indicating that smaller cations typically have higher hydration energies. The discussion highlights a common misconception regarding the relationship between ionic size and hydration energy.

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https://www.toppr.com/iit-jee/chemistry/s-block-elements/cheatsheet/
in this under sub heading properties of alkali metals third definition hydration of ions
it is written as Smaller size of cation, larger is the extent of hydration and hydration energy order is-
Cs+>Rb+>K+>Na+>Li+
but according to the table cs cation has greatest radius so hydration energy should be least but the order shows different story.
 
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gracy said:
Smaller size of cation, larger is the extent of hydration and hydration energy order is-
Cs+>Rb+>K+>Na+>Li+

Technically it is correct - hydration enthalpies are always negative, and -264 kJ/mol (for Cs+) > -520 kJ/mol (for Li+) :wink:

But I doubt that's what they meant, you are right, the list should be reversed.
 
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