The reality is that all gasses interact with each other slowing down each others movements as they bump around and pass next to each other in space. A scientist by the name of Johannes van der Waals proposed a new equation to compensate for this behavior, in his Ph.D. thesis. The new equation called the van der Waals equation is as follows. The constant b corrects the equation for volume and is equal to the volume occupied by a mole of molecules. The constant a corrects for the intermolecular forces between the atoms.
Water molecules form hydrogen bonds with polar molecules, and each other.
This is because water is a polar molecule due to the position of the hydrogen atoms when they are bonded to the oxygen. The hydrogen side of the molecule aquires a positive charge and the oxygen side aquires a negative charge. It is this ability to form hydrogen bonds that gives water its comparatively high melting and boiling points. Water boils at 100 degrees Celsius, and freezes at 0 degrees Celsius. It is this ability of the hydrogen bonds that also allows water to be less dense as solid ice then as liquid water.