What is intermolecular distance in water?

Question

I am wondering what is an average intermolecular distance in liquid water (say under normal pressure and room temperature).

I need just order of magnitude. A reference would be helpful.

Answer 1

One mole of liquid water has a mass of 18 grams (two hydrogen atoms with mass 1, one oxygen with 16), occupies 18cm³ and contains roughly 6e23 molecules.

So, the average single molecule occupies 3e-23cm³. If you assume that to be a cube (good enough for the order of magnitude), you get a dimension of 3.1e-8cm, or 0.31 nanometer.

And that's the average distance between the water molecules.

Answer 2

In liquids the molecules are packed densely. Therefore the intermolecular distance is about equal to the size of the molecules (which for water is around $3 \cdot 10^{-10}$ m).