Properties of Water A Polar Molecule Water is made up of two hydrogen atoms (H) and one oxygen atom (O). (H 2 O) Electrons are shared in covalent bonds. Oxygen pulls more powerfully on the negatively charged electrons. This gives the oxygen end a slightly negative charge. Hydrogen end has a slightly positive charge. Therefore, water molecules act like tiny magnets and stick together. Polarity Explains several of Waters Unique Properties Cohesion Adhesion Surface tension Density anomaly Ability to dissolve things High specific heat Capillary attraction Large temperature range at which water is liquid Cohesion Cohesion causes water to form drops and prevents vaporization. Adhesion Adhesion allows water to cling to other surfaces. Surface Tension Surface tension is caused by cohesion. Molecules on the surface are attracted to the sides and downward. This causes the surface to act as if it has a film on it. Unlike other substances, solid water is less dense than liquid water, allowing it to float. Water expands when frozen. Density Anomaly Density is Mass /Volume The density of pure water is 1.0g/cm 3 at 4C If an object has a density of less than 1.0g/cm 3, it floats. Greater than 1.0g/cm 3, it sinks. Density may be changed by- Adding another substance (Salt water is more dense than fresh) Changing the temperature In warm water, the molecules move faster and are farther apart, making it less dense. In cool water, the molecules move slower, making it more dense. The differences in density cause ocean currents. Universal Solvent Water dissolves more things than any other liquid. High Specific Heat Water is able to absorb large amount of thermal energy with showing large changes in temperature. Large bodies of water moderate the temperature of the nearby land. Capillary Attraction Capillary attraction allows a water to rise against gravity when enclosed in a very narrow tube or in contact with an absorbent material States of Water Water is the only compound on Earth that exists naturally in all three states. Liquid- water, solid- ice, and gas- water vapor Water has a very large temperature range in which it exists as a liquid. Water boils at 100C (212F) Water freezes at 0C (32F) ICE has a definite shape. Molecules are more open than in liquid water. Ice is less dense than liquid water, so it floats. LIQUID WATER takes the shape of its container. WATER VAPOR cannot be seen. It expands or contracts to fill available space. H2OH2O