We can see this electronegativity difference as we begin to cool
the gaseous HF and LiF molecules. Nothing happens to HF until the
temperature decreases to 19.5°C, at which point the gas molecules
are moving so slowly that they can be trapped by forces between
molecules and condensed into a liquid.
The individual molecules remain intact in the liquid, with the forces
between them being a combination of van der Waals interactions and
hydrogen bonds from one H to the F on a neighboring molecule.
At -83°C, molecular motion becomes so slow that these forces
freeze the HF molecules into a crystalline solid. Even in the solid,
individual HF molecules remain, held together by the forces between