Intermolecular forces between water molecules cause surface tension. Molecules on the surface of a liquid are attracted to molecules within and between them. The molecules inside the liquid have no attractive force because other molecules surround them. The Phase Change of Water and the Specific Properties of Each Phase Water has the very unique physical property of being the only natural substance that occurs as a solid, liquid, or gas. Changing water from one phase to another requires a large amount of energy. Water at temperatures at or below 0°C is a solid (ice). Water at 0°C or higher is a liquid. Water at 100°C is a gas (water vapour). GasWater vapor is compressible, expandable, and takes up much more space than other phases. It moves freely and has no defined shape or volume. LiquidLiquid water does not expand as easily as gases. It will take the shape of the container it is placed in and the movement of the particles will be more limited than that of gases, but less than that of solids. SolidSolid water is hard and less dense than its liquid form, which is rare. The particles do not change shape or expand/contract with the container they are placed in