Question

Which of the following has the highest Boiling Point?

• A. Chloromethane
• B. Fluoromethane
• C. Bromomethane
• D. Iodomethane

Answer 1

The Correct Option is D

The correct option is (D): Iodomethane.

Boiling Point and Intermolecular Forces:
The boiling point of a compound is influenced by various factors, including the strength and nature of intermolecular forces. These forces are responsible for holding the molecules together, and overcoming them requires energy, which is reflected in the boiling point. In this case, we compare the compounds based on the polarity and strength of the halogen bonding.

Effect of Halogen Size on Boiling Point:
As we move down the halogen group, the size and polarizability of the halogen atoms increase. Larger atoms, such as iodine, are more polarizable, which means they can induce stronger van der Waals forces (a type of intermolecular force). These forces are responsible for holding the molecules together in the liquid phase. As a result, stronger van der Waals forces lead to a higher boiling point. Therefore, we observe that:

• Fluoromethane (B): Has the smallest halogen (fluorine), which induces weaker van der Waals forces and therefore has the lowest boiling point.
• Chloromethane (A): Chlorine is larger than fluorine, but still smaller than bromine and iodine. Thus, it has a higher boiling point than fluoromethane.
• Bromomethane (C): Bromine is larger and more polarizable than chlorine, resulting in stronger intermolecular forces and a higher boiling point than chloromethane.
• Iodomethane (D): Iodine, being the largest and most polarizable halogen in this group, induces the strongest van der Waals forces, resulting in the highest boiling point.

Conclusion:
Therefore, Iodomethane (D) is expected to have the highest boiling point among the given compounds due to the strongest intermolecular forces (van der Waals forces) resulting from the larger, more polarizable iodine atom.