Bonding Unit Learning Goal #5: Identify the how intermolecular forces of hydrogen bonds in water affect a variety of physical, chemical, and biological phenomena.

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.

States of Water

States of Water

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. Water molecules are dipolar (meaning that its electrons are not shared equally due to covalent bonding) and this generates hydrogen bonding between atoms. As a result its structure gives water many important properties such as its thermal, high surface tension, incompressibility and cohesiveness.

Importance to Living Organisms Water has many useful biological roles such as being a solvent, a coolant, an insulator, as support, a lubricant and a reagent. Moreover water is used in chemical reactions, transporting and it provides a suitable environment for aquatic animals to habitat.

Surface Tension The force needed to overcome intermolecular attractions and break through the surface of a liquid or spread the liquid out. The net inward force make the surface of the drop contract and seem to toughen, behaving like a sort of skin.

Capillary Action Results from the competition between intermolecular forces between the molecules of liquid and between the liquid and the tube that contains it.

Water and Heat Water must absorb or release the most heat of most common substances to change temperature. That is why it takes a long time for a swimming pool to heat up or cool down.

Evaporation/ Condensation 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.

Essential Questions How does hydrogen bonding affect water’s properties? Describe how hydrogen bonding in water affects so many aspects of life on Earth.