Question

Draw the structure of white phosphorous and red phosphorus . Which one of these two types of phosphorus is more reactive and why ?

Answer 1

Hint: White phosphorus and red phosphorus are allotropic forms of phosphorus . Allotropes are different structural modifications of an element , the atoms of the element are bonded together in a different manner .

Complete step by step answer:
Complete step by step answer :

The above structure is of white phosphorus .
It exists as $P_4$ units . The four $s{p}^3$ hybridised phosphorus atoms lie at the corners of a regular tetrahedron with each angle equal to ${60}^{\circ }$ . Each phosphorus atom is linked to three other phosphorus atoms by covalent bonds so that each atom completes its octet .

The above structure is of red phosphorus .
Like white phosphorus it also exists as $P_4$ tetrahedra but these are joined together through covalent bonds to give a polymeric structure as shown in the above diagram .

Although white and red phosphorus are allotropic forms of phosphorus only they differ widely in their chemical reactivity .
White phosphorus is more reactive than red phosphorus because of angle strain in it , as angle is much smaller at only ${60}^{\circ }$ in it than the normal tetrahedral angle whereas red phosphorus is more stable due to polymeric structure .
white phosphorus is stored under water to protect it from air while red is stable in air .

Note:
Angle strain occurs when bond angles deviate from the ideal bond angles to achieve maximum bond strength in a specific chemical conformation . In case of white phosphorus it deviates highly from the ideal tetrahedral angle $({109}^{\circ }{28}^{\prime })$ and therefore is highly reactive.