Bonding Unit Water Properties

Water Formula = H2O Molecular Mass = 18 State at Room Temperature = Liquid Melting Point = 0 oC Boiling Point = 100 oC Less Dense as a solid

Intermolecular Forces Creates Order Hydrogen Bonding In pure water, each water molecule may form hydrogen bonds with four other water molecules.

Hydrophobic –vs- Hydrophilic Nonpolar molecules that repel the water molecules are said to be hydrophobic. molecules forming ionic or a hydrogen bond with the water molecule are said to be hydrophilic.

Surfactants Surfactants are compounds that lower the surface tension between two liquids or between a liquid and a solid.

States of Water

Universal Solvent Water is capable of dissolving a variety of different substances, which is why it is such a good solvent. water is called the "universal solvent" because it dissolves more substances than any other liquid. This is important to every living thing on earth.

Importance to Living Organisms Next to oxygen, water is essential for all living organisms on Earth. It is a major component in cells, which make up all living organisms; therefore approximately 60% to 95% of living organisms are water.

Importance to Living Organisms Water has many useful biological roles such as: being a solvent a coolant an insulator as support a lubricant a reagent. Water is used in chemical reactions for transporting providing a suitable environment

Surface Tension The tendency of liquids to keep a low surface area. Liquids with stronger cohesion (intermolecular forces) tend to have higher surface tension. Water has a very high surface tension.

Adhesion –vs- Cohesion Adhesion is the attraction of molecules of one kind for molecules of a different kind. it can be quite strong for water, especially with other molecules bearing positive or negative charges. Cohesion refers to the attraction of molecules for other molecules of the same kind. Water molecules have strong cohesive forces thanks to their ability to form hydrogen bonds with one another.

Capillary Action Results from the adhesive force between the molecules of liquid and the side of the tube. Adhesive forces are the attractive forces between two unlike molecules.

Specific Heat The heat required to raise the temperature of the unit mass of a given substance one degree.

Water and Heat Water absorbs or releases the most heat of the common substances when changing temperature. That is why it takes a long time for a swimming pool to heat up or cool down.

Water and Heat Water's high heat capacity is a property caused by hydrogen bonding among water molecules. When heat is absorbed, hydrogen bonds are broken and water molecules can move freely. When heat is released, the hydrogen bonds are formed and considerable amount of energy is released.

Phase Change Evaporation (liquid to a gas) is endothermic (energy-absorbing) because intermolecular forces must be overcome. You must add heat to boil water. Condensation (gas to a liquid) is exothermic (energy-releasing) You must cool water vapor to get it to turn into liquid water.

Phase Change

Ice Ice floats because it is about 9% less dense than liquid water. In other words, ice takes up about 9% more space than water, so a liter of ice weighs less than a liter water.

Ice The heavier water displaces the lighter ice, so ice floats to the top. One consequence of this is that lakes and rivers freeze from top to bottom. This allows fish to survive even when the surface of a lake has frozen over. If ice sank, the water would be displaced to the top and exposed to the colder temperature, forcing rivers and lakes to fill with ice and freeze solid.