Which allotrope of phosphorus is the most reactive?
a) White phosphorus
b) Metal phosphorus
c) Red phosphorus
d) Beta-black phosphorus
The correct answer and explanation is :
The correct answer is:
a) White phosphorus
Explanation:
White phosphorus is the most reactive allotrope of phosphorus. This is primarily due to its molecular structure and the strained bonds in its P4 tetrahedral structure. Each molecule of white phosphorus consists of four phosphorus atoms arranged in a tetrahedral shape, with each atom bonded to the others by single bonds. These bonds are highly strained and unstable, making white phosphorus highly reactive.
When white phosphorus is exposed to air, it readily reacts with oxygen to form phosphorus pentoxide (P4O10), a highly exothermic reaction. The reactivity of white phosphorus is also influenced by its tendency to easily form free radicals, which increases its reactivity with various substances, including water and halogens. White phosphorus is also highly flammable and can spontaneously combust in the presence of air, which further demonstrates its high reactivity.
Additionally, white phosphorus is extremely toxic and can cause severe health issues if inhaled or ingested. It also reacts vigorously with metals, especially alkali and alkaline earth metals, forming various compounds. Due to its high reactivity, it is handled with great care in controlled environments.
In comparison, other allotropes of phosphorus exhibit much lower reactivity:
- Red phosphorus: This allotrope is much more stable than white phosphorus and is less reactive due to its polymeric structure, which involves a network of linked P atoms. Red phosphorus does not combust spontaneously and is more stable under normal conditions.
- Metal phosphorus: This allotrope is formed under high pressure and has metallic properties, including electrical conductivity. It is generally more stable than white phosphorus and not as reactive.
- Beta-black phosphorus: This is a stable allotrope that exhibits semi-metallic properties and is quite inert compared to white phosphorus. Its stability makes it less reactive.
Thus, white phosphorus is by far the most reactive allotrope of phosphorus.