8. I Water molecules form an open crystalline structure in ice When water freezes the water molecules arrange themselves in a Six-sided crystalline structure Increased structural orderliness usually means increased density Solids and crystals have high structural orderliness and are thus denser than liquid and non-crystalline materials. But water is exception (dense) dless dense later molecules in the liquid phase are arranged more compactly than water molecules in the solid phase, where they form an open crystalline structure8.1 Water molecules form an open crystalline structure in ice When water freezes, the water molecules arrange themselves in a six-sided crystalline structure. Increased structural orderliness usually means increased density. Solids and crystals have high structural orderliness and are thus denser than liquid and non-crystalline materials. But water is exception