Question

Simple question. Trying to think through why Hydrogen Iodide has a higher melting point than Hydrogen Fluoride.

Answer 1

What's the difference between heavy and light? It's harder to get heavy stuff to move in general, similar idea here. HI is much heavier than HF, so it takes more energy in the form of heat to shake the atoms strongly enough for them to resist their electrostatic forces keeping them together.

A simple analogy is to think of shaking a box of sand vs shaking a box of rocks, but don't think about this picture too hard, it's not perfect, just to give an idea that individual particles of sand are small and easy to move around like HF while rocks are more like HI molecules.