Why reducing nature of lithium metal is greatest and sodium being least powerful ruducing nature?

there are two factors which effect reducing nature

1.ionisation energy

2.hydration enthalpy

 

hydration enthalpy is the energy released when a bond is formed between ion and the water

the lone pair on oxygen and the positive ion are attracted towards each other

hydration enthalpy depends on

1.size

2.charge

in simple words it depends on charge density which is charge/volume

if charge increases the hydration enthalpy increases

if size decreases the hydration enthalpy increases

in 1A group lithium has the least size

so it acts as powerful reducing agent

despite of its more ionisation energy

 

 

From the ionization energies we might expect lithium to be the weakest of the alkali metals as a reducing agent in water. However, the standard reduction potentials indicate that it is the strongest. This reversal results mainly from the very large energy of hydration of the small Li+ ion. Please note that the reaction takes place in water and not in a gas phase. What this means is that because of its relatively high charge density, the Li+ ion very effectively attracts water molecules. A large quantity of energy is released in the process, favoring the formation of the Li+ ion and making lithium a strong reducing agent in aqueous solution.