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Why does a more polarizable halogen increase the boiling point of an alkyl halide?

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A more polarizable halogen increases the boiling point of an alkyl halide because it enhances the strength of intermolecular attractive forces known as London dispersion forces.1

Polarizability refers to how easily the electron cloud of an atom can be distorted by nearby electric fields. As the atomic number of a halogen increases—moving from fluorine to iodine—the atom becomes larger and its electron cloud becomes more polarizable.1

These more easily distorted electron clouds facilitate stronger London dispersion forces, which are attractive forces arising from instantaneous fluctuations in electron distribution. Because these intermolecular forces are stronger, more thermal energy is required to overcome them, resulting in a higher boiling point for the compound.12