5. Gain and Loss of Electrons   Previous PageNext Page
       Ions and Salts

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 molecules.

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