Problem 128 - A Complete Resource Book in Chemistry for JEE Main

Question

The incorrect statement about structure of white phosphorus is (a) It has four P- P single bonds. (b) It has six P- P single bonds. (c) It has PPP angle of \(60^{\circ}\) (d) It has four lone pairs of electrons.

Step-by-Step Solution

Answer

The incorrect statement is option (a): it has four P-P single bonds.

Step 1: Understanding White Phosphorus

White phosphorus is a molecule composed of four phosphorus atoms forming a tetrahedral shape. Each phosphorus atom forms three single bonds with neighboring phosphorus atoms, and has one lone pair.

Step 2: Analyzing the Options

Let's analyze each option given in the question. - **Option (a)** states that there are four P-P single bonds. This is incorrect because each phosphorus atom in the tetrahedral P4 molecule forms three bonds, giving a total of six P-P single bonds in the structure. - **Option (b)** states there are six P-P single bonds. This is correct as explained. - **Option (c)** indicates a PPP angle of 60°, consistent with the tetrahedral geometry. - **Option (d)** correctly states that there are four lone pairs, one on each phosphorus atom.

Step 3: Identifying the Incorrect Statement

From Step 2, we identified that option (a) incorrectly states that white phosphorus has four P-P single bonds. The molecule actually has six P-P single bonds.

Key Concepts

Tetrahedral Geometry

The structure of white phosphorus is distinctly notable due to its unique tetrahedral geometry. In chemistry, a tetrahedral shape is defined by four atoms symmetrically arranged around a central point, forming a cage-like structure with triangular faces. In the case of white phosphorus (P₄), all four phosphorus atoms are positioned at the vertices of a tetrahedron.
This geometric configuration is due to the optimal spatial arrangement that minimizes repulsion among the atoms and their bonding electrons. It is important to note that these tetrahedral angles are typically around 109.5° for perfect tetrahedrons. However, in white phosphorus, the structure is somewhat strained due to the small size of the tetrahedron, resulting in less standard bond angles.

P-P Single Bonds

The bonding structure of white phosphorus revolves around P-P single bonds. In the tetrahedral P₄ molecule, each phosphorus atom is bonded to three other phosphorus atoms, forming a total of six P-P single bonds within the molecule.
This might seem surprising at first glance, as each vertex only directly connects to three others, but since each phosphorus atom is involved in bonding with three other atoms, calculating the total bonds requires considering these shared connections. White phosphorus, thus, clearly demonstrates how complex bonding patterns can arise in simple geometric figures through shared electrons.

Lone Pairs of Electrons

Within the white phosphorus molecule, each phosphorus atom possesses a lone pair of electrons. These lone pairs are the non-bonding pairs of electrons that are not involved in forming P-P single bonds.
Lone pairs play a crucial role in the chemical reactivity and geometry of a molecule, often influencing its physical and chemical behavior. Though they do not participate directly in bonding, lone pairs can affect the shape of the molecule by exerting additional repulsion, contributing to the smaller bond angles in white phosphorus compared to an ideal tetrahedral geometry.

Bond Angles in Phosphorus

The bond angles found in the structure of white phosphorus are distinct. Typically, in tetrahedral structures formed by sp³ hybridized atoms, the bond angles are approximately 109.5°. However, in P₄, the bond angles are significantly smaller due to the geometrical constraints of tying four phosphorus atoms in such a compact tetrahedral configuration.
This leads to bond angles of roughly 60°, which is less than ideal and introduces strain within the molecule. The small internal bond angles create a stressed environment causing white phosphorus to be relatively more reactive. Understanding these angles provides insight into the molecule's chemical properties, illuminating why it behaves as it does under various chemical conditions.