Question

Maximum number of covalent bonds formed by N and P are

• A. 3, 5
• B. 3, 6
• C. 3, 4, 5
• D. 3, 4, 6
• E. None of the above

Hint:

Covalency is the number of shared electron pairs. Nitrogen can never form 5 bonds (e.g., \(NCl_5\) does not exist), but Phosphorus can.

Answer 1

Answer: (E)

Concept: The maximum covalency of an element depends on the availability of valence orbitals.
• Nitrogen (N) is in the second period; it only has \(2s\) and \(2p\) orbitals (total 4 orbitals).
• Phosphorus (P) is in the third period; it has \(3s, 3p\), and vacant \(3d\) orbitals.

Step 1: Analyze Nitrogen.
Nitrogen can form 3 covalent bonds (like in \(NH_3\)) and 1 coordinate bond using its lone pair (like in \(NH_4^+\)). Because it lacks $d$-orbitals, its maximum covalency is strictly 4. It cannot expand its octet to form 5 bonds.

Step 2: Analyze Phosphorus.
Phosphorus can use its vacant \(3d\) orbitals to expand its octet. It can form 3 bonds (\(PCl_3\)), 5 bonds (\(PCl_5\)), and even 6 bonds in coordination complexes like \([PF_6]^-\).

Step 3: Conclusion.
The maximum covalency for N is 4 and for P is 6. Since no option provides the pair (4, 6), the answer is "None of the above."