S and O both are non-metals in the oxygen family , but their melting points are targely different , O = 90 K and S = 718 K . This is because

Options

A. S is large in size than O
B. S exhibits more oxidation state `+ 2 , + 4 ` and `+6` whereas O exhibits only `-2` and `+2` oxidation states
C. O exists as diatomic molecule whereas S exists as polyatomic molecule `(S_(8))`
D. S has more allotropes than O

Answer

To explain the difference in melting points between sulfur (S) and oxygen (O), we can break down the reasoning into a few key steps:

### Step-by-Step Solution:

1. **Identify the Elements and Their Properties**:
- Oxygen (O) and sulfur (S) are both non-metals and belong to the same group in the periodic table (Group 16 or the oxygen family).
- Oxygen has a melting point of 90 K, while sulfur has a significantly higher melting point of 718 K.

2. **Consider Atomic Size**:
- The atomic size of sulfur is larger than that of oxygen. This is due to the position of these elements in the periodic table; sulfur is located below oxygen in the group.

3. **Examine Molecular Structure**:
- Oxygen primarily exists as diatomic molecules (O2), which are held together by weak van der Waals forces.
- In contrast, sulfur exists as a cyclic octatomic molecule (S8), which has a more complex structure and stronger intermolecular forces.

4. **Catenation and Bonding**:
- Sulfur has a greater ability for catenation (the ability to form chains of atoms) due to its larger size and the presence of vacant d-orbitals. This allows sulfur to form stable S8 molecules.
- Oxygen, being smaller and having lone pairs that repel each other, does not have significant catenation power and exists as O2.

5. **Intermolecular Forces**:
- The S8 molecules experience stronger van der Waals forces due to their larger size and greater molecular weight compared to O2 molecules. This leads to a higher melting point for sulfur.

6. **Conclusion**:
- The significant difference in melting points between sulfur and oxygen can be attributed to the molecular forms they adopt (S8 vs. O2) and the resulting intermolecular forces. Sulfur's larger size and ability to form stable chains contribute to its higher melting point.

### Final Answer:
The melting points of sulfur and oxygen differ significantly because sulfur exists as S8 molecules, which have stronger intermolecular forces due to their larger size and catenation ability, while oxygen exists as O2 molecules, which are held together by weaker forces.

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