1. WATER ¾ of the Earth is covered with it Exists on Earth as a solid, liquid AND gas POLAR!!!

2. Do you remember the 3 types of bonds we taught earlier in the year? 2 1. Metallic 2. Ionic 3. Covalent- actually there are two types… 1. Polar Covalent 2. Nonpolar Covalent How do you know which type will form???

3. So actually- there are four types of bonds you must know: 3 1. Metallic- 1. metal with a metal 2. Ionic 1. Metal with a nonmetal

4. The four types of bonds you must know: 4 3. Nonpolar Covalent: -Nonmetal with a nonmetal -If two of the same element

5. The four types of bonds you must know: 5 4. Polar Covalent: -Nonmetal with a nonmetal - Both are different elements

6. 6

7. Water background rewind  What elements are in a water molecule?  What type of bond will form between them?  How do you know it will be a polar covalent bond?  _______________ with a ____________

8. Polarity of Water  A water molecule is a polar molecule with opposite ends of the molecule with opposite charges.  oxygen is more electronegative so it pulls on the electrons more  the OXYGEN end has a slight negative charge.  The HYDROGEN end has a slight positive charge. 8

9. This leads to a new type of “bond”…  Called a…

10. 10 Hydrogen bond

11. Hydrogen Bonds  Not really a bond.  Occur between molecules (not within)  Bonds within water molecules are POLAR COVALENT!!!

12. HYDROGEN BONDS  As far as BOND go, they are very weak, about 1/20 th as strong as covalent bonds.  They form, break, and reform with great frequency 12

13.  Each water molecule can form hydrogen bonds with up to four neighbors.

14. Polar Covalent- green Hydrogen bonds- orange

15. 15 Hydrogen bonds affect the properties of water

16. Special Arrangement:  Water molecules arrange themselves in a very specific way…  WHY??? 16

17. OPPOSITES ATTRACT

18. BUT Like charges repel each other… 18

19. 19 What two ends of the molecule attract each other? Hydrogen and Oxygen What will be repelled by each other? O + O and H + H Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.1

20. Which will form? Circle which will form on your notes packet…

21. Organisms Depend on H bonds…  Cohesion – water molecules sticking to each other (by H bonds)  plays a key role in the transport of water against gravity in plants  Adhesion- water molecules stick to other things  Like the meniscus! 21

22. 22 Surface tensionMeniscus-adhesion Surface Tension- cohesion

23. Hydrogen Bonds affect the DENSITY of water  USUALLY a solid is more dense than the liquid or gas form:

24. NOT TRUE FOR WATER!  Due to the H bonds- water actually EXPANDS ( and is less dense than water) when it FREEZES!!!

25. Density of Water 25 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.

26. Are you afraid of water? 26  What do you think the following two words mean?  Hydrophilic  Hydrophobic  Hydro means water, philic and phobic refer to whether or not it “likes” water

27. Hydrophilic vs Hydrophobic  Hydrophilic  Any substance that likes water (WATER-LOVING) Ionic or polar substances Most hydrophilic substances dissolve in water (ex salt)  Hydrophobic: any substance that doesn’t like water  (WATER –FEARING) Usually nonpolar/non-ionic substance (ex-oil)

28. “Like Dissolves Like” 28  Polar Solutions (like water) are able to dissolve other polar molecules as well as ionic compounds. Why?  Likewise, nonpolar solutions (like oil) will not dissolve polar and ionic compounds and will instead dissolve NONPOLAR molecules.