JEE MainChemistryp Block Elements (Group 15, 16, 17 & 18)
When ammonia reacts with an excess of a specific halogen gas ( X ₂ ), it forms a trihalide ( Y ) which is a thermodynamically stable, non-explosive gas at room temperature. Identify the halogen X ₂ and the primary reason for the high stability of the product Y .
Options
- AX ₂ = Cl ₂ ; the large size of chlorine reduces interelectronic repulsions around the nitrogen atom.
- BX ₂ = F ₂ ; the absence of d-orbitals in the valence shell of nitrogen prevents its expansion.
- CX ₂ = I ₂ ; the low electronegativity of iodine makes the N - I bond highly covalent and stable.
- DX ₂ = F ₂ ; the strong N - F bond is formed due to highly effective 2 p -2 p orbital overlap.
Correct answer
D. X ₂ = F ₂ ; the strong N - F bond is formed due to highly effective 2 p -2 p orbital overlap.
Step-by-step solution
The reaction of ammonia with halogens depends on the specific halogen and the reactant in excess. When NH ₃ reacts with excess Cl ₂ , it forms NCl ₃ , which is an explosive yellow liquid. When NH ₃ reacts with I ₂ , it forms NI ₃ NH ₃ , which is a highly explosive dark solid. When NH ₃ reacts with excess F ₂ , it forms NF ₃ , which is a stable, non-explosive gas. Thus, the halogen X ₂ is F ₂ , and the product Y is NF ₃ . The exceptional thermodynamic stability of NF ₃ compared to other nitrogen trihalides is due to