Question

The large difference between the melting and boiling points of oxygen and sulphur may be explained on the basis of

• A. Atomic size
• B. Atomicity
• C. Electronegativity
• D. Electron gain enthalpy

Hint:

The atomicity of sulfur \( (S_8) \) results in stronger intermolecular forces compared to oxygen \( (O_2) \), leading to a higher melting and boiling point for sulfur.

Answer 1

The Correct Option is B

The large difference between the melting and boiling points of oxygen (O₂) and sulfur (S₈) is best explained by their atomicity. 

1. Atomicity: Atomicity refers to the number of atoms in a molecule. Oxygen exists as a diatomic molecule (O₂), meaning it consists of two atoms. In contrast, sulfur commonly exists as an octatomic molecule (S₈), consisting of eight atoms.
2. Intermolecular Forces: The structure of sulfur as S₈ makes it larger and more complex, which results in stronger van der Waals forces of attraction between its molecules compared to O₂. These stronger forces require more energy to overcome, leading to higher melting and boiling points for sulfur compared to oxygen.
3. Explanation of Options:
   • Atomic Size: While size affects melting and boiling points, the difference in atomicity is more significant in this context.
   • Electronegativity: Electronegativity does not directly affect the melting or boiling points in this case.
   • Electron Gain Enthalpy: This property is related to the energy change when an electron is added to an atom and is irrelevant to the discussion of melting and boiling points.
4. Conclusion: The correct explanation for the large difference between the melting and boiling points of oxygen and sulfur is their atomicity. The molecular forms (O₂ vs. S₈) account for the difference in the strength of intermolecular forces, thus affecting their melting and boiling points.

Answer 2

Given: Oxygen and sulfur belong to the same group in the periodic table, but their melting and boiling points differ significantly. The primary reason for this difference is atomicity, i.e., the number of atoms in a molecule of the element.

Factors Affecting Melting and Boiling Points

1. Atomic Size

- The atomic size of sulfur is larger than oxygen. However, atomic size alone does not explain the large difference in their melting and boiling points. Therefore, this factor is not the main reason.

2. Atomicity

- Oxygen exists as \( O_2 \), a diatomic molecule, whereas sulfur exists as \( S_8 \), an eight-atom molecule. - The larger atomicity of sulfur leads to stronger intermolecular forces due to more atoms interacting with each other. - The stronger intermolecular forces result in higher boiling and melting points for sulfur compared to oxygen. - **Conclusion**: The primary reason for the difference in melting and boiling points is atomicity.

3. Electronegativity

- Oxygen is more electronegative than sulfur. While electronegativity does play a role in bonding and molecular interactions, it does not significantly affect the large difference in the melting and boiling points of oxygen and sulfur.

4. Electron Gain Enthalpy

- Oxygen has a higher electron gain enthalpy than sulfur. While this difference is important for understanding ionization and electron affinity, it does not explain the large discrepancy in melting and boiling points.

Conclusion:

The correct answer is **(2) Atomicity**. The molecular structure of sulfur with \( S_8 \) leads to stronger intermolecular forces, resulting in a higher melting and boiling point compared to oxygen.