Question

What is the role of intermolecular forces of attraction?

Answer 1

To keep molecules together.

Explanation:

All molecules are attracted to each other by dispersion forces. This force makes it so that molecules don't drive apart from each other, but stay together. Only when a large enough external force is applied can this force be broken (at least temporarily). Now this force is different for every molecule.

Water, `H_2O`, for example, does not only have the regular dispersion intermolecular force, but also has "hydrogen-bonding" interactions between the hydrogen atom of the one molecule and the oxygen atom of the next molecule.

This makes water much more tightly-held together than other fluids. Those interactions are what you feel when you jump in a pool, but hit the water surface with your body horizontal. It hurts, because the water wants to stay together instead of letting you through.