In a liquid, the particles are very close together, but can move around each other. In a solid, the particles are packed together. Depending on the substance, the solid particles can either be very well-ordered (crystalline) or have little or no long-range order (amorphous). When water solidifies, the water molecules arrange themselves in a hexagonal shape. The reason for this is because of hydrogen bonding between the O and the H atoms between the different water molecules. Therefore, the water molecules are more distant from one another in solid form than they are in liquid form. This leads to ice having a lower density than does water, and hence ice floats on water.