Question

Oxides of nitrogen have open chain structure while those of phosphorus have closed chain or cage structures. Why is it so? Illustrate with one structural example for each type of oxides.

Answer 1

1. Nitrogen forms oxides with open-chain structures because it can form strong pπ-pπ multiple bonds (double or triple bonds) due to the absence of vacant d-orbitals. This stabilizes linear or open-chain structures.
2. Phosphorus lacks effective pπ-pπ bonding and has vacant d-orbitals, allowing it to expand its coordination and form stable cage or closed ring structures.
3. Example: Nitrogen oxide – Nitrous oxide (N₂O) has an open chain structure.
4. Example: Phosphorus oxide – Phosphorus pentoxide (P₄O₁₀) has a closed cage structure composed of tetrahedral P₄ units interconnected by oxygen atoms.

Thus, the difference in bonding abilities and the availability of d-orbitals explain the structural differences.