Problem 142 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following statements are correct for the \(\mathrm{P}_{4}\) molecule? (a) Its reacts with nitrogen to form a phosphorous nitrogen polymer (b) The electron affinity of phosphorous is negative (c) The P-P bond distance are equal (d) The P-P-P bond angles are \(60^{\circ}\).

Step-by-Step Solution

Answer

Statements (b), (c), and (d) are correct.

Step 1: Evaluate Statement (a)

Phosphorus often interacts with nitrogen to form various compounds, but a reaction specifically forming a phosphorus-nitrogen polymer is not typical for \( \mathrm{P}_4 \) under standard conditions. Without specific context or reactants, this statement is not generally correct for \( \mathrm{P}_4 \).

Step 2: Evaluate Statement (b)

The electron affinity of phosphorus is indeed negative, which is typical for nonmetals that generally have a tendency to gain electrons. Therefore, statement (b) is correct.

Step 3: Evaluate Statement (c)

\( \mathrm{P}_4 \) is structured as a tetrahedron, where each phosphorus atom is equidistant from its neighboring phosphorus atoms. Thus, the P-P bond distances are indeed equal. Therefore, statement (c) is correct.

Step 4: Evaluate Statement (d)

In \( \mathrm{P}_4 \), each P-P-P bond angle is \( 60^{\circ} \) due to its tetrahedral arrangement. Therefore, statement (d) is correct.

Key Concepts

P4 Molecule

Phosphorus, an essential element in chemistry, forms various allotropes, one of which is the tetrahedral \( \mathrm{P}_4 \) molecule. Understanding its structure helps to uncover how phosphorus behaves in different chemical environments.
The \( \mathrm{P}_4 \) molecule is arranged in a tetrahedral shape. This means each phosphorus atom is at the corner of a tetrahedron. It is bonded to three other phosphorus atoms by P-P bonds.

• The structure is perfectly symmetrical.
• All P-P bonds are equal in length.
• The bond angles are all around \(60^{\circ} \).

This tight bonding arrangement, while stabilizing \( \mathrm{P}_4 \), makes it a unique and interesting molecule to study in the context of phosphorus chemistry.

Phosphorus Compounds

Phosphorus is known to form a wide variety of compounds owing to its high reactivity. The versatility of phosphorus compounds is crucial for understanding its role in both biological and industrial processes.
Common phosphorus compounds include phosphates, phosphines, and phosphoric acid. These compounds are significant in various applications:

• Phosphates: Found in fertilizers, they are vital for plant growth.
• Phosphines: Used in organophosphorus chemistry, often in the formation of ligands and catalysts.
• Phosphoric Acid: An ingredient in many soft drinks and used in the manufacture of fertilizers.

The ability of phosphorus to form different oxidation states (from \(-3\) to \(+5\)) allows it to partake in various chemical reactions, enhancing its utility across different chemical domains.

Chemical Bonding in Phosphorus

In the realm of chemical bonding, phosphorus exhibits several unique characteristics. The tetrahedral shape of the \( \mathrm{P}_4 \) molecule is tied directly to how phosphorus bonds with itself and other elements.
The \( \mathrm{P}_4 \) molecule is quite stable due to its specific chemical bonding:

• Each phosphorus atom uses its 3p orbitals to bond with three others, forming strong covalent P-P bonds.
• The tetrahedral arrangement allows for a uniform distribution of electron density around the molecule.

When forming compounds, phosphorus can participate in different types of bondings, such as:

• Covalent - as seen in \( \mathrm{PCl_3} \), where phosphorus bonds covalently with chlorine.
• Ionic - often in phosphates like \( \mathrm{Ca_3(PO_4)_2} \), where the phosphates are ionically bonded to calcium.

This flexibility in bonding ensures phosphorus's essential role in both organic and inorganic chemistry.

Electron Affinity of Phosphorus

Electron affinity refers to the energy change when an electron is added to a neutral atom, forming an anion. For phosphorus, this property is naturally negative, indicating that energy is released when it gains an electron.
As a nonmetal, phosphorus has a smaller attraction to electrons when compared to other elements like oxygen or fluorine. This is because phosphorus has a larger atomic radius which results in weaker attraction for additional electrons at its outer shell.

• Despite being negative, phosphorus's electron affinity is less negative compared to other nonmetals.
• This is due to increased electron repulsion in its p-shell after the addition of an extra electron.
• Negatively impacting its ability to gain electrons, which influences the kind of bonds it forms.

Nonetheless, the negative electron affinity underscores its ability to participate in electron-sharing or covalent bonds, rather than forming anions frequently.