Question

Why does phosphorus form less stable P₄ molecules instead of P₂ molecules?

a. P₂ molecules violate the octet rule.
b. P₄ molecules have higher bond energy.
c. P₂ molecules are too reactive.
d. P₄ molecules follow the electron configuration of nitrogen.

Answer 1

Phosphorus forms P₄ molecules due to its three-valence bonding pattern in accordance with the octet rule and lower reactivity compared to P₂, unlike nitrogen, which forms a stable triple-bonded N₂ due to its lack of d orbitals.

Step-by-step explanation:

The reason why phosphorus prefers to form P₄ molecules instead of P₂ molecules is due to its tendency to form three bonds in accordance with the octet rule. The tetrahedral structure of white phosphorus consists of P₄ molecules, with each phosphorus atom forming three bonds with other phosphorus atoms and completing the octet. This contrasts with nitrogen, which forms a triple bond in N₂ molecules, due to its ability to create strong pi (π) bonds in addition to a sigma (σ) bond, resulting in a very stable diatomic molecule. The high reactivity of P₂ molecules can also be considered, which leads to the formation of the less reactive P₄ form in white phosphorus.

Now, comparing the situation with nitrogen, nitrogen has no valence d orbitals and thus cannot extend its octet, while phosphorus can utilize its d orbitals; however, in its most stable form, phosphorus still follows the octet rule and forms P₄ molecules. In contrast to the potential reactivity of a P₂ molecule, a P₄ molecule offers a stable configuration that is less prone to react spontaneously.