I'm wondering if the orientation of two hydrogens to one oxygen (they line up opposite each other as I understand it) has anything to do with why the solid crystalline state is lighter (less molecules per volume in the crystalline form).
As I understand it, the two hydrogen molecules do not go to opposite ends of the oxygen molecule. The angle between them is less than 180 degrees. This means that a water molecule has a "positive" side and a "negative" side. This is what allows a microwave oven to work. The alternating magnetic field grabs onto the water molecule by the polar ends, and causes the molecule to oscillate back and forth as the microwave magnetic field changes. This movement produces friction that produces heat. If the two hydrogen molecules were at opposite ends of the water molecule, there would be no polar ends on the water, and we would have no microwave ovens.
Don't know.