1. Water

2. Water three A water molecule (H 2 O), is made up of three atoms --- one oxygen and two hydrogen. H H O

3. Properties of Water Polar molecule Cohesion and adhesion High specific heat Density – greatest at 4 o C Universal solvent of life

4. oxygen atom attracts more electrons In each water molecule, the oxygen atom attracts more than its "fair share" of electrons oxygennegative The oxygen end “acts” negative hydrogen positive The hydrogen end “acts” positive POLAR Causes the water to be POLAR neutral Zero Net Charge However, Water is neutral (equal number of e- and p+) --- Zero Net Charge Polarity of Water In a water molecule two hydrogen atoms form single polar covalent bonds with an oxygen atom. Gives water more structure than other liquids –Because oxygen is more electronegative, the region around oxygen has a partial negative charge. –The region near the two hydrogen atoms has a partial positive charge. A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.

5. HYDROGEN BONDS Hold water molecules together Each water molecule can form a maximum of 4 hydrogen bonds They form, break, and reform with great frequency Extraordinary Properties that are a result of hydrogen bonds. –Cohesive behavior –Resists changes in temperature –High heat of vaporization –Expands when it freezes –Versatile solvent

6. Organisms Depend on Cohesion Attraction between particles of the same substance (why water is attracted to itself) Attraction between particles of the same substance ( why water is attracted to itself) Results in Surface tension (a measure of the strength of water’s surface) Results in Surface tension (a measure of the strength of water’s surface) Produces a surface film on water that allows insects to walk on the surface of water Produces a surface film on water that allows insects to walk on the surface of water Hydrogen bonds hold the substance together, a phenomenon called cohesion

7. Adhesion Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.3 Attraction between two different substances. Attraction between two different substances. Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Water will make hydrogen bonds with other surfaces such as glass, soil, plant tissues, and cotton. Capillary action-water molecules will “tow” each other along when in a thin glass tube. Capillary action-water molecules will “tow” each other along when in a thin glass tube. Which gives water the ability to “climb” structures Example: transpiration process which plants and trees remove water from the soil, and paper towels soak up water.

8. Moderates Temperatures on Earth What is kinetic energy? Heat? Temperature? What is specific heat? Celsius Scale at Sea Level 100 o CWater boils 37 o CHuman body temperature 23 o CRoom temperature 0oC0oCWater freezes Water stabilizes air temperatures by absorbing heat from warmer air and releasing heat to cooler air. Water can absorb or release relatively large amounts of heat with only a slight change in its own temperature.

9. Three-fourths of the earth is covered by water. The water serves as a large heat sink responsible for: 1.Prevention of temperature fluctuations that are outside the range suitable for life. 2.Coastal areas having a mild climate 3.A stable marine environment Specific Heat is the amount of heat that must be absorbed or lost for one gram of a substance to change its temperature by 1 o C.

10. Evaporative Cooling The cooling of a surface occurs when the liquid evaporates (Under Armor) This is responsible for: –Moderating earth’s climate –Stabilizes temperature in aquatic ecosystems –Preventing organisms from overheating

11. Density of Water Most dense at 4 o C Contracts until 4 o C Expands from 4 o C to 0 o C The density of water: 1.Prevents water from freezing from the bottom up. 2.Ice forms on the surface first—the freezing of the water releases heat to the water below creating insulation. 3.Makes transition between season less abrupt.

12. –When water reaches 0 o C, water becomes locked into a crystalline lattice with each molecule bonded to to the maximum of four partners. –As ice starts to melt, some of the hydrogen bonds break and some water molecules can slip closer together than they can while in the ice state. –Ice is about 10% less dense than water at 4 o C. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.5

13. Water is Less Dense as a Solid WaterIce

14. Buoyancy Buoyancy is the ability of a fluid to exert an upward force on an object floating in it. Buoyant force (upward) must be greater than gravitational force (downward) in order for an object to float Objects with a lower density than water will float in water. Metal is more dense than water, so the shape of a boat helps it float.

15. Buoyancy and the Titanic

16. Solvent for Life Solution –Solute –Solvent Hydrophilic –Ionic compounds dissolve in water –Polar molecules (generally) are water soluble Hydrophobic –Nonpolar compounds

17. Solutions & Suspensions Water is usually part of a mixture. Water is usually part of a mixture. There are two types of mixtures: There are two types of mixtures: – Solutions – Suspensions

18. Solution Ionic compounds disperse as ions in water Ionic compounds disperse as ions in water Evenly distributed Evenly distributed SOLUTE SOLUTE – Substance that is being dissolved SOLVENT SOLVENT – Substance into which the solute dissolves

19. Solution

20. Suspensions don’t dissolve but separate Substances that don’t dissolve but separate into tiny pieces. Water keeps the pieces suspended Water keeps the pieces suspended so they don’t settle out.

21. The pH Scale concentration of H + ions Indicates the concentration of H + ions 0 – 14 Ranges from 0 – 14 7 is neutral pH of 7 is neutral 0 up to 7 is acid pH 0 up to 7 is acid … H + above 7 – 14 is b pH above 7 – 14 is basic… OH - 10X Each pH unit represents a factor of 10X change in concentration pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6 pH 3 is 10 x 10 x 10 (1000) stronger than a pH of 6

22. Acids and Bases An acid is a substance that increases the hydrogen ion concentration in a solution. Any substance that reduces the hydrogen ion concentration in a solution is a base. –Some bases reduce H + directly by accepting hydrogen ions. Strong acids and bases complete dissociate in water. Weak acids and bases dissociate only partially and reversibly.

23. Acids Strong Acids have a pH of 1-3 Strong Acids have a pH of 1-3 Produce lots of H + ions Produce lots of H + ions

24. Bases Strong Bases 11 to 14 Strong Bases have a pH of 11 to 14 lots of OH - ions Contain lots of OH - ions and fewer H+ ions

25. Buffers Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization). Weak acids or bases that react with strong acids or bases to prevent sharp, sudden changes in pH (neutralization). Produced naturally by the body to maintain homeostasis Produced naturally by the body to maintain homeostasis Weak Acid Weak Base