Question

Why lithium is the only alkali metal to form a nitride directly?

Answer 1

Lithium is the smallest atom among alkali metals. ... When Lithium reacts with nitrogen gas at room temperature (N2), it forms Lithium Nitride (Li3N) which is stable, because the lattice energy released from the formation of Li3N is high enough to make the overall reaction exothermic.

Answer 2

Explanation:

(a) On moving down the group, the atomic and ionic sizes of alkali metals increases. As the size increases, the extent of hydration decreases.

The extent of hydration and ionic mobility are inversely proportional.

(b) Small sized Li ion is most compatible with nitride ion. Thus, in formation of lithium nitride, large amount of lattice energy is released. This energy overcomes the high amount of energy required for formation of nitride ion.