Question

Question) It is given that lithium forms nitride so how do other alkali elements when react with nitrogen ?

Answer 1

Dear Student,
Lithium is the only alkali metal that forms a stable nitride on reaction with nitrogen under standard conditions. Nitrogen is highly unreactive molecule the strong triple bond holds the N₂ molecule very tightly and large amount of energy will be needed to break N₂ bond to form N^3- ions. For the formation of nitride the requirement is first of all the ionization energy to make the metal cation and Second of all the energy needed to break the N bond. This energy requirement is met by the Lattice energy released on the formation of metal nitride.
The lattice energy release depends upon the size of ion and charge. The charge for all alkali metals is same but the size of lithium is smallest.Therefore the lattice energy released for lithium is maximum .This released energy makes the formation of lithium nitride highly exothermic.
While other alkali metals will form nitrides at a higher temperature as the reaction is endothermic(lattice energy is very low) and the nitrides formed will be highly unstable.
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