Group 15 Elements

To determine the maximum covalency of a non-metallic group 15 element with the weakest E-E bond, we need to understand the concepts of covalency and the nature of bonds within group 15 elements.

Step 1: Understand Covalency

Covalency refers to the number of electron pairs an atom can share with other atoms. In the case of group 15 elements (Nitrogen, Phosphorus, Arsenic, Antimony, Bismuth), non-metals tend to share electrons to form covalent bonds.

Step 2: Group 15 Elements and Covalency

Group 15 elements have 5 electrons in their valence shell. The maximum covalency is generally equal to the number of unpaired electrons in the outer shell after attaining an expanded octet under specific conditions. For these elements, the maximum covalency observed in heavier group 15 elements is due to the availability of d-orbitals.

Step 3: Analyzing Weakest E-E Bond

Among group 15 elements, the element with the weakest E-E bond is nitrogen (N₂ has a very strong triple bond), so it does not qualify here. Phosphorus, on the other hand, generally forms P₄ units with relatively weaker single P-P bonds, making it suitable for this context.

Step 4: Phosphorus Covalency

Phosphorus can expand its covalency by utilizing d-orbitals. Therefore, the maximum covalency of phosphorus is 5, as observed in compounds like PF₅. However, taking into account only covalent bonds available with consideration of typical orbitals (without d-orbital expansion under normal bonding), the practical observed maximum is 4, as seen in PCl₄⁺ ions.

Conclusion: The maximum covalency of a non-metallic group 15 element with the weakest E-E bond, which is phosphorus, is 4.