This document provides an overview of key chemistry concepts related to water and its importance for life. It discusses water's unique properties including its ability to form hydrogen bonds, act as a solvent, have lower density as a solid allowing ice to float, store and release heat via its high specific heat and heat of vaporization, and ionize into H+ and OH- ions determining pH. These special properties of water, especially its prevalence as the solvent for life processes and its role in moderating temperatures on Earth, make it uniquely suited to supporting life.

1. 2009-2010 The Chemistry of Life

2. Why are we studying chemistry? Chemistry is the foundation of Biology

3. The World of Elements H C O N P S Na Mg K Ca

4. Elements & their valence shells Elements in the same column have the same valence & similar chemical properties Remember some food chainsare built on reducing O to H2O & some on reducing S to H2S

5. – – – Chemical reactivity Atoms tend to complete a partially filled valence shell or empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds

6. – – H2 (hydrogen gas) Covalent bond Bonds in Biology Hydrogen bond H2O Weak bonds hydrogen bonds attraction between + and – hydrophobic & hydrophilic interactions interactions with H2O van derWaals forces ionic Strong bonds covalent bonds sharing electrons H2O

8. example: hydrocarbons = CxHx

9. methane (CH4 )Lots of energy stored…& released balanced, stable,good building block

11. example: water = H2O

12. oxygen has stronger “attraction” for the electrons than hydrogen

13. oxygen has higher electronegativity

14. water isa polar molecule

15. + vs – poles

16. leads to many interesting properties of water…+ – – – – +

18. attraction between positive H in one H2O molecule to negative O in another H2O

19. also can occur wherever an -OH exists in a larger molecule

20. Weak bond

23. Elixir of Life Special properties of water 1. cohesion & adhesion surface tension, capillary action 2. good solvent many molecules dissolve in H2O hydrophilic vs. hydrophobic 3. lower density as a solid ice floats! 4. high specific heat water stores heat 5. high heat of vaporization heats & cools slowly Ice!I could use more ice!

25. H bonding between H2O molecules

26. water is “sticky”

27. surface tension

28. drinking straw

29. Adhesion

30. H bonding between H2O & other substances

31. capillary action

32. meniscus

33. water climbs uppaper towel or clothTry that with flour…or sugar…

34. How does H2O get to top of trees? Transpiration is built on cohesion & adhesion

36. polar H2O molecules surround + & –ions

38. substances have attraction to H2O

40. substances that don’t have an attraction to H2O

41. polar or non-polar?Oh, lookhydrocarbons! fat (triglycerol)

43. H bonds form a crystalIce!I could use more ice! And this hasmade all the difference!

45. surface ice insulates water below

46. allowing life to survive the winter

47. if ice sank…

48. ponds, lakes & even oceans would freeze solid

49. in summer, only upper few inches would thaw

50. seasonal turnover of lakes

52. high specific heat

53. takes a lot to heat it up

54. takes a lot to cool it down

55. H2O moderates temperatures on EarthSpecific heat& climate 4. Specific heat

56. Evaporative cooling 5. Heat of vaporization Organisms rely on heat of vaporization to remove body heat

58. H+ splits off from H2O, leaving OH–

59. if [H+]= [-OH], water is neutral

60. if [H+]> [-OH], water is acidic

61. if [H+]< [-OH],water is basic

62. pH scale

63. how acid or basic solution is

64. 1 7  14H2O  H+ + OH–

65. pH Scale H+ Ion Concentration Examples of Solutions pH 100 Hydrochloric acid 0 10–1 1 10–2 2 Stomach acid, Lemon juice Vinegar, cola, beer 10–3 3 Tomatoes 10–4 4 10–5 5 Black coffee, Rainwater 10–6 6 Urine, Saliva 7 Pure water, Blood 10–7 Seawater 8 10–8 Baking soda 10–9 9 Great Salt Lake 10–10 10 10–11 Household ammonia 11 10–12 12 Household bleach 10–13 13 Oven cleaner 10–14 Sodium hydroxide 14 tenfold changein H+ ions pH1  pH2 10-1 10-2 10 times less H+ pH8  pH7 10-8 10-7 10 times more H+ pH10  pH8 10-10 10-8 100 times more H+

66. 9 8 7 6 Buffering range 5 pH 4 3 2 1 0 1 0 3 4 5 2 Amount of base added pH of cells must be kept ~7 pH affects shape of molecules shape of molecules affect function therefore pH affects cellular function Control pH by buffers reservoir of H+ donate H+ when [H+] falls absorb H+ when [H+] rises Buffers & cellular regulation