Question

Nitrogen exists as diatomic molecule and phosphorus as P₄. Why?

Explain giving reason of the following:

Nitrogen exists as a diatomic molecule N₂, whereas phosphorus exists as a tetra atomic molecule P₄.

Answer 1

1. Nitrogen exists as a diatomic molecule having a triple bond between the two N-atoms.
2. This is due to its small size, which allows it to form pπ-pπ multiple bonds with itself and with carbon/oxygen as well.
3. On the other hand, phosphorus, due to its larger size, does not form multiple pπ-pπ bonds with itself.
4.  It prefers to form P-P single bonds, and hence it exists as a tetrahedral P₄ molecule.

Answer 2

1. Since nitrogen is tiny and has a high electronegativity, it is very likely to form multiple pπ-pπ bonds with itself.
2. As a result, it is a diatomic molecule (N₂) that tends to form an N=N triple bond.
3. Conversely, phosphorus has almost no propensity to create pre-pre multiple bonds with itself because of its bigger size and lower electronegativity.
4. Rather, it favours creating P-P single bonds to create a tetrahedral P₄ molecule.