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Do you remember? What are the two types of bonds? How do you predict which type will form? What will O and H form? Why? –covalent bonds between H and O. –Because they are both nonmetals –But they have a special type of covalent bond called…POLAR. 2

3 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 –So…the region around oxygen has a partial negative charge. –The region near the two hydrogen atoms has a partial positive charge.

4 Hydrogen bonding

5 –The slightly negative regions of one molecule are attracted to the slightly positive regions of nearby molecules, forming a hydrogen bond. –Each water molecule can form hydrogen bonds with up to four neighbors. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 3.1 OPPOSITES ATTRACT

6 HYDROGEN BONDS The hydrogen bonds joining water molecules are weak, about 1/20 th as strong as covalent bonds. They form, break, and reform with great frequency

BUT Like charges repel each other… 7

H bonds give water some cool properties… 8

9 Organisms Depend on Cohesion Cohesion among water molecules plays a key role in the transport of water against gravity in plants Adhesion, clinging of one substance to another, contributes too, as water adheres to the wall of the vessels. Hydrogen bonds hold the substance together, a phenomenon called cohesion

10 Surface tension

11 Density of Water 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 Ice, water, vapor

13 Hydrogen bonding (electric attraction) IceLiquid

14 Are you afraid of water? What do you think the following two words mean? –Hydrophilic –Hydrophobic

15 “Like Dissolves Like” 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.

16 So what about oil and water?

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

There are three types of bonds you must know: 1.Ionic 2.Nonpolar Covalent 3.Polar Covalent How do you know which type will form??? 18

There are three types of bonds you must know: 1.Ionic 1.Metal with a nonmetal 19

There are three types of bonds you must know: Nonpolar Covalent: -Nonmetal with a nonmetal -If two of the same element NOT -or two elements that are NOT Nitrogen, Oxygen or Fluorine. 20

There are three types of bonds you must know: Polar Covalent: -Nonmetal with a nonmetal -If Nitrogen, Oxygen or Fluorine are one of the elements, they are VERY electronegative and will hog the electrons… Therefore NOF’s create POLAR COVALENT BONDS! 21

22 pH pH = – log [H+] Log scale means 10X change per unit! [H+]= M [H+]= M

23 pH Scale Measures the degree of acidity (0 – 14) Most biologic fluids are in the pH range from 6 – 8 Each pH unit represents a tenfold difference (scale is logarithmic) –A small change in pH actually indicates a substantial change in H + and OH - concentrations.

24 Buffers A substance that eliminates large sudden changes in pH. Buffers help organisms maintain the pH of body fluids within the narrow range necessary for life. –Are combinations of H + acceptors and donors forms in a solution of weak acids or bases –Work by accepting H + from solutions when they are in excess and by donating H + when they have been depleted.

25 Acid Precipitation Rain, snow or fog with more strongly acidic than pH of 5.6 West Virginia has recorded 1.5 East Tennessee reported 4.2 in 2000 Occurs when sulfur oxides and nitrogen oxides react with water in the atmosphere –Lowers pH of soil which affects mineral solubility – decline of forests –Lower pH of lakes and ponds – In the Western Adirondack Mountains, there are lakes with a pH <5 that have no fish.

26 How would carbon bond with H? CH4 How would it look? CH4 contains nonpolar covalent bonds because although C and H are different elements, they pull on the electrons equally.