Boiling Points

[noree_jauregui]

Why does HI not have a lower boiling point than HBr if I is farther away from H in the periodic table?

[Kevin_Conrad_2E]

As you go down the halogen group in the periodic table, the atoms become larger and more polarizable. This means that the electron cloud around the halogen atom can be more easily distorted, resulting in stronger London dispersion forces. Iodine (I) is larger and more polarizable than bromine (Br), so the dispersion forces in HI are stronger than in HBr.

While it is true that longer bonds are generally weaker, which might suggest easier boiling, in this case, the increased polarizability of the larger halogen (I) more than compensates for this effect, leading to overall stronger intermolecular forces in HI than in HBr.

[noree_jauregui]

Thank you so much!