Question

The correct order of hydration enthalpies of alkali metal ions is:
1. Li⁺ > Na⁺ > K⁺ > Cs⁺ >Rb⁺ 
2. Na⁺ > Li⁺ > K⁺ >Rb⁺ > Cs⁺
3. Na⁺ > Li⁺ > K⁺ > Cs⁺ >Rb⁺
4. Li⁺ > Na⁺ > K⁺ >Rb⁺ > Cs⁺ 

Answer 1

Correct Answer - Option 4 : Li⁺ > Na⁺ > K⁺ >Rb⁺ > Cs⁺ 

Concept:

The energy released as a result of the formation of new bonds between ions and water molecules is called hydration enthalpy.

Hydration enthalpies of alkaline earth metal ions decrease with the increasing ionic size down the group.

The ionic size is when the atom loses or gains electrons to become negatively charged (anions) or positively charged (cations) ions. When atoms lose or gain electrons, the size of the ion is not the same as the original atom.

According to periodic table, the ionic size in increasing order is:

Li < Na < K < Rb < Cs

Thus, correct order of hydration enthalpies of alkali metal ions is:

Li > Na > K > Rb > Cs