Why is elemental nitrogen N2 and elemental phosphorus P4 even if the two elements belong to the same group in the periodic table?

Answer 1

Because elements in the first row (second period) form multiple bonds much more readily than elements in the second row (third period).

N2 is a gas, with the molecule triple-bonded. But P4 is a solid, with each atom at a corner of a tetrahedron, and single bonds to the other three atoms.

Similarly O2 is a gas with double-bonded molecules, but S8 is a solid with sulfur atoms in 8-membered rings. And most dramatically of all, carbon dioxide is a gas with double-bonded atoms: O=C=O , while silicon dioxide is quartz -- a network structure with only single bonds. Each silicon atom is surrounded by and single-bonded to four oxygen atoms; each oxygen atom is single-bonded to two silicon atoms.

Answer 2

Although both nitrogen and phosphorus belong to the same group (Group 15) in the Periodic Table, they have different atomic structures and properties. Nitrogen atoms prefer to form strong triple covalent bonds, resulting in N2 molecules. Phosphorus atoms, on the other hand, tend to form weaker single covalent bonds, leading to P4 molecules in the elemental state.