Problem 117 - A Complete Resource Book in Chemistry for JEE Main

Question

White phosphorus \(\left(\mathrm{P}_{4}\right)\) has 1\. six P-P sigma bonds 2\. four P-P single bonds 3\. four lone pairs of electrons 4\. PPP angle of \(60^{\circ}\) (a) \(1,2,3\) (b) \(2,3,4\) (c) \(1,3,4\) (d) all are correct

Step-by-Step Solution

Answer

Option (c), statements 1, 3, and 4 are correct.

Step 1: Understand the Structure of White Phosphorus

White phosphorus (\(\mathrm{P}_{4}\)) consists of four phosphorus atoms connected in a tetrahedral shape, forming a three-dimensional molecular structure. Each phosphorus atom in this structure shares one bond with each of the other three phosphorus atoms.

Step 2: Analyze P-P Sigma Bonds

In \(\mathrm{P}_{4}\), each phosphorus atom forms three single bonds with other phosphorus atoms. Since there are four phosphorus atoms, there are a total of six P-P sigma bonds in the structure. These bonds are single bonds without any double or triple bonds.

Step 3: Check for P-P Single Bonds

As established, each phosphorus atom forms three single bonds with adjacent phosphorus atoms. However, we have a total of six P-P single bonds, not four, as each distinct P-P pair forms one single bond outright.

Step 4: Evaluate Lone Pairs of Electrons

Each phosphorus atom in \(\mathrm{P}_{4}\) has one lone pair of electrons. Given there are four phosphorus atoms, the molecule as a whole has four lone pairs of electrons.

Step 5: Determine PPP Angle

From the tetrahedral geometry of white phosphorus, the bond angle between any three consecutive phosphorus atoms is \(60^{\circ}\). This is due to the molecular strain in the tetrahedral form of \(\mathrm{P}_{4}\).

Step 6: Compare Each Statement with Facts

- Statement 1 (six P-P sigma bonds) is true.- Statement 2 (four P-P single bonds) is not true as there are six such bonds.- Statement 3 (four lone pairs of electrons) is true.- Statement 4 (PPP angle of \(60^{\circ}\)) is true.

Step 7: Choose the Correct Options

Considering the analysis, options (c) which includes statements 1, 3, and 4, are correct. Statement 2 is incorrect as it suggests fewer bonds than actually exist.

Key Concepts

P-P sigma bonds

White phosphorus, known chemically as \( \mathrm{P}_4 \), has a fascinating molecular structure that creates a number of P-P sigma bonds. Sigma bonds are a type of covalent bond that arise when two atomic orbitals combine directly along the axis connecting the two bonding nuclei. In \( \mathrm{P}_4 \), each phosphorus atom is bonded to three other phosphorus atoms. This creates

• three P-P sigma bonds per phosphorus atom,
• leading to a total of six P-P sigma bonds in the entire molecule.

These sigma bonds are characterized by their rotational symmetry around the axis and are the strongest type of covalent bond, adding stability to the \( \mathrm{P}_4 \) molecule. It is important to note that all these bonds are single bonds, where only a pair of electrons is shared between the atoms, with no double or triple bonds present in the structure.

lone pairs of electrons

In the molecule of white phosphorus \( (\mathrm{P}_4) \), each phosphorus atom has a lone pair of electrons. A lone pair consists of two valence electrons that are not shared with another atom and are not involved in the bonding process. The presence of these lone pairs is significant because:

• They contribute to the overall electron density around the phosphorus atoms,
• Influence the geometry of the molecule by repelling other electron pairs,
• Affect the chemical reactivity and physical properties of the substance.

Given that there are four phosphorus atoms in \( \mathrm{P}_4 \), each possessing one lone pair, the molecule collectively contains four lone pairs of electrons. These lone pairs are responsible for some of the unique properties observed in white phosphorus, such as its high reactivity and distinct tetrahedral shape.

PPP bond angle

The molecular geometry of \( \mathrm{P}_4 \) is quite intriguing due to its triangular tetrahedral shape. One essential feature of this shape is the bond angle found among the phosphorus atoms, known as the PPP bond angle. The PPP bond angle in white phosphorus is precisely

• \( 60^{\circ} \),

which is considerably smaller than typical bond angles in a standard tetrahedron. This small bond angle results from strain within the molecule, as the atoms are forced closer together than usual. Such strain increases the instability of \( \mathrm{P}_4 \), making it more reactive compared to less constrained molecular structures. Understanding the PPP bond angle helps in predicting the reactivity and properties of white phosphorus, which are important for its practical applications and safety considerations in handling.