1. PROPERTIES OF WATER The Universal Solvent

2. The Water Molecule Simple tri-atomic molecule, H 2 O Each O-H bond is highly polar due to the high electronegativity of Oxygen Bond angle = 105° H 2 O has a bent shape, meaning the O-H bonds due not cancel = Polar Molecule

3. The Water Molecule δ is the Greek symbol for Delta δ + means there is a partial positive charge δ – means there is a partial negative charge Since there is a large difference in the electronegativity of the Oxygen and Hydrogen atoms, the element is Polar

4. The Water Molecule Water’s bent shape and ability to Hydrogen Bond give it special properties High Surface Tension Low Vapor Pressure High Specific Heat High Heat of Vaporization High boiling point Water molecules are attracted by Dipole Interactions What are dipole interactions?

5. High Surface Tension Surface Tension: the inward pull or force that tends to minimize the surface area of a liquid Water forms round droplets The greater the molecular force, the higher the surface tension, the more spherical the droplet Water acts like it has a skin Hydrogen bonding creates a large network of bonds between adjacent molecules

6. Surface Tension Water molecules hydrogen bond to one another due to electrostatic attraction Molecules in the middle are pulled in various direction to bond with adjacent molecules Molecules at the surface are pulled downward and to the side since water is not attracted to air

7. Surface Tension Glass has polar molecules and has the ability to hydrogen bond This attracts water molecules and causes them to be drawn up a cylinder wall Plastics are non-wetting; have no attraction to water molecules

8. Can we decrease Surface Tension? Use a Surfactant – Surface Active Agent Also called a “wetting agent”, like detergent or soap How does it work? It interferes with Hydrogen Bonding

9. Low Vapor Pressure Vapor Pressure is caused by molecules that escape the surface of a liquid and enter gaseous state Hydrogen Bonding holds water molecules close so there is a low tendency to escape Why is this important?

10. Specific Heat Capacity Water has a high heat capacity (also termed specific heat) It requires a large amount of energy/heat to be absorbed to change it’s temperature Allows moderation of daily temperatures Warm days: water absorbs heat from warmer environment decreasing air temperature Cool Nights: transfer of heat from water to cooler environment increasing air temperature

11. Evaporation and Condensation Water absorbs large amounts of heat as it evaporates or vaporizes Water gives off large amounts of heat as it condenses Water = 18.02 g/mol, Liquid rather than a gas, an important exception, BP is 100°C Extensive Hydrogen bonding requires more heat to disrupt bonds

12. Ice As most liquids cool, they tend to contract (get smaller) Water does not act in this manner, Why? It will decrease in volume until it reaches about 4°C, then it starts to expand This occurs as water molecules slow down arranging themselves in honeycomb crystal shapes This expansion causes the volume of the ice to increase while the mass remains the same Ice has a 10% lower density than water