# Why are hydrated lithium ions' radii larger than hydrated sodium ions' radii?

Why are hydrated lithium ions' radii larger than hydrated sodium ions' radii i.e. $$r_\ce{Li+(aq)}>r_\ce{Na+(aq)}$$?

If ionic radii increase down the group i.e. $$r_\ce{Li+} then the radii of hydrated ions also increase down the group i.e. $$r_\ce{Li+(aq)}. But according to my class notes, The radii of hydrated ions are larger than those of gaseous ions. The radii of hydrated ions decrease as the group. I'm not sure I understand. But, according to the class notes and Quora answers, how can the size of an ion alter the hydration radii?

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.

As the size of ion increases its polasiation tendency decreases therefore the tendency to polarise nearby water molecules decreases hence decreasing its hydration radii. This effect can be seen by observing the trend of hydartion radii in alkali metal ions.

• Look around the site, it was discussed recently. Dec 19, 2021 at 15:37
• Please check you greater/smaller than signs. Are they like you intended? Dec 19, 2021 at 18:55
• I have corrected it. Thanks.
– user119959
Dec 20, 2021 at 14:13
• This current profile is unregistered. Is this your another profile? chemistry.stackexchange.com/users/100905/huzaifa-abedeen Dec 21, 2021 at 1:24