I read in Voet & Voet that the hydrogen bonds are at least 0.5 angstrom shorter than the calculated van der waals distance. As I understand, van der waals distance is the distance of closest approach between two atoms/molecules. How are two water molecules able to break this to get closer to each other and form hydrogen bonds?
We also know that ice is less dense than liquid water. In ice, water molecules are hydrogen bonded to each other and the distance between them is shorter than van der waals distance. but it liquid water not all of them is hydrogen bonded and it should be ideally at a minimum distance of van der waals and the density should be less. What is making the water molecules to interact closer to make liquid water more dense than ice?