Question

Why do the oxides of phosphorus and other heavier elements of group 15 have cage structures?

Answer 1

1. The heavier group 15 elements (P, As, Sb, Bi) have oxides that do not form multiple bonds like nitrogen oxides.
2. Nitrogen can form strong pπ-pπ multiple bonds, but heavier elements are unstable for such bonding.
3. Due to a lack of stable multiple bonding, these elements form oxides with single bonds only.
4. The oxides are thus arranged in cage-like polyatomic structures involving single bonds for stability.
5. This cage structure helps minimise strain and maximise stability of the molecule.

So, the oxides of phosphorus and heavier group 15 elements have cage structures because these elements cannot form stable multiple bonds and instead form stable single-bonded cages.