JEE Main 2022 · 24 June · evening · Single correct · +4 / −1
PCl₅ is well known, but NCl₅ is not. because,
- (a) nitrogen is less reactive than phosphorus.
- (b) nitrogen doesn't have d-orbitals in its valence shell.
- (c) catenation tendency is weaker in nitrogen than phosphorus.
- (d) size of phosphorus is larger than nitrogen.
Answer and solution
Answer (b) nitrogen doesn't have d-orbitals in its valence shell.
Solution
Chemistry ma’am · 4 steps
Five bonds need five orbitals, and nitrogen's valence shell has only four to offer.
- What PCl5 needs. In PCl₅, phosphorus forms five P–Cl bonds, so 10 electrons sit around it. That needs five orbitals, which P gets by sp³d hybridisation using one of its empty 3d orbitals.
- What nitrogen has. Nitrogen's valence shell is n = 2, which contains only 2s and 2p: four orbitals in all. There is no 2d subshell, so nitrogen cannot hold more than 8 electrons.
- Maximum covalency. With only four orbitals, nitrogen can form at most four bonds, as in NH₄⁺. That is why NCl₃ exists but NCl₅ does not.
- So. The reason is the missing d orbitals in nitrogen's valence shell, which is option (b).
The idea to keep. Period 2 elements like N, O and F cannot form more than four bonds because the n = 2 shell has no d subshell. Expanded octets begin only from period 3.
Answer from the NTA final answer key. Solution by PrepWiser.