Question -
Answer -
(a)┬аOn moving down the alkaligroup, the ionic and atomic sizes of the metals increase. The given alkalimetal ions can be arranged in the increasing order of their ionic sizes as:
Li+┬а< Na+┬а< K+┬а< Rb+┬а< Cs+
Smaller the size of an ion, the more highlyis it hydrated. Since Li+┬аis the smallest, it gets heavilyhydrated in an aqueous solution. On the other hand, Cs+┬аis the largest and so itis the least hydrated. The given alkali metal ions can be arranged in thedecreasing order of their hydrations as:
Li+┬а> Na+┬а> K+┬а> Rb+┬а> Cs+
Greater the mass of a hydrated ion, thelower is its ionic mobility. Therefore, hydrated Li+┬аis the least mobileand hydrated Cs+┬аis the most mobile. Thus, the givenalkali metal ions can be arranged in the increasing order of their mobilitiesas:
Li+┬а< Na+┬а< K+┬а< Rb+┬а< Cs+
(b)┬аUnlike the otherelements of group 1, Li reacts directly with nitrogen to form lithium nitride.This is because Li+┬аis very small in size and so its sizeis the most compatible with the N3тАУ┬аion. Hence, thelattice energy released is very high. This energy also overcomes the highamount of energy required for the formation of the N3тАУ┬аion.
(c)┬аElectrode potential(E┬░) of any M2+/M electrode depends upon three factors:
(i)Ionisation enthalpy
(ii)Enthalpy of hydration
(iii)Enthalpy of vaporisation
Thecombined effect of these factors is approximately the same for Ca, Sr, and Ba.Hence, their electrode potentials are nearly constant.