The Chemistry of Life

1. The Chemistry of Life Part II – Water

2. Water on Earth

3. The Properties of Water • For a planet to support life, abundant liquid water would have to be available • Water can exist in all 3 physical states on earth • Liquid • Solid • Gas

4. Why does the electron stay in orbit around the nucleus?

5. The Properties of Water • A molecule consists of two or more atoms held together by chemical bonds. • A chemical bond involves the sharing of two electrons. • Water is a molecule made up of two hydrogen atoms and one oxygen atom that are bonded together by shared electrons.

6. In a water molecule, the two hydrogen atoms each share one electron with the oxygen. This gives each hydrogen atom two electrons in their outer shell (the ideal number for shell 1), and the oxygen atom eight in its outer shell (the ideal number for shell 2).

7. The Properties of Water • Oxygen is more electronegative (electron-pulling) than hydrogen. • The electrons in water spend more time near the nucleus of the oxygen atom than near the nuclei of the hydrogen atoms. • δ- symbolizes a partial negative charge. • δ+ symbolizes a partial negative charge.

9. The Properties of Water • The unequal sharing of electrons makes water a polar molecule, since different regions (poles) of the molecule have different charges. • When atoms of a molecule carry no charge, they are nonpolar. • Fats are nonpolar

11. The Properties of Water • The weak attraction between the hydrogen atom and the oxygen atom is a hydrogen bond. • Hydrogen bonding is a weak chemical bond occurring between hydrogen and another atom based on the attraction of partial charges for each other.

13. The Properties of Water • Water molecules are attracted to each other because of the opposite charges. • This attraction creates hydrogen bonds. • These strong bonds determine almost every physical property of water and many of its chemical properties.

14. 4 Emergent Properties of Water Water is a Polar Molecule • Water is Cohesive and Adhesive • Water Resists Change in Temperature. • Water Expands When It Freezes. • Ice floats on liquid water • Water is densest at 4oC • Water is the solvent for chemistry of life.

15. Cohesion Water molecules stick to each other. Attraction between water molecules is greater than attraction between water and air. Creates a surface tension (film) Permits water to hold up substances heavier and denser than itself. Steel needle carefully placed on the surface of a glass of water will float.

16. Cohesion of water molecules permits the flow of water in streams and rivers. • Surface tension is essential for the transfer of energy from wind to water to create waves which are necessary for rapid oxygen diffusion in lakes and seas. • Some aquatic insects such as this water strider (predators on smaller invertebrates) rely on surface tension to walk on water.

17. Adhesion • Water molecules bind to many other substances such as glass, cotton, plant or animal tissues and soils. • Ex: Thin glass tube - when the molecules at the edge reach for and adhere to the molecules of glass just above them, they tow other water molecules along with them due to cohesion. The water surface, then, pulls the entire column of water to a new level until the downward force of gravity is too great to be overcome. • This process is called capillary action.

18. Adhesion • Adhesion allows the flow of water through the vascular tissues of plants and the flow of blood through blood vessels.

19. Laminar viscosity: friction between layers of water. Flow is fastest in middle, and slowest near edges of stream and bottom due to friction between layers. Multiple spatial niches in streams

20. Eddy viscosity: mixing of layers creates turbulence that keeps small organisms suspended in water. Planktonic inverts also have morphologies and/or behaviors that keep them from sinking rapidly.

21. Plankton swirling in turbulent flow of ocean eddy

22. High Heat Capacity • Water absorbs or releases more heat than many substances for each degree of temperature increase or decrease. • Warms slowly • Cools slowly • Makes evaporative cooling possible • Sweating • Evapotranspiration in plants

23. High Heat Capacity • Water’s high specific heat is linked to hydrogen bonding. • Much of the heat energy is used to disrupt the hydrogen bonds before the water molecules can begin moving faster. • When the temperature of the water drops slightly, many hydrogen bonds form, releasing a considerable amount of energy in the form of heat.

24. High Heat Capacity • The specific heat is the amount of heat that must be absorbed or lost for one gram of that substance to change its temperature by 1oC • Therefore, the specific heat of water is defined as 1cal/gram/oC

25. High Heat Capacity • Water vapor forms a kind of global blanket that helps to keep the earth warm. • Heat radiated from the sun-warmed surface of the earth is absorbed and held by the vapor. • Water vapor contributes to global warming • Is it a greenhouse gas?

26. High Heat Capacity • Large bodies of water, such as the oceans or the Great Lakes, have a profound influence on climate. • Heat reservoirs and heat exchangers • Sources of moisture that falls as rain and snow over adjacent land masses. • When water is colder than the air, precipitation is curbed, winds are reduced, and fog banks are formed.

27. Chicago’s Weather • There are two geographical factors that contribute to Chicago's weather. • Lake Michigan: 450 miles long, 80 miles wide, 900 feet deep. • Location: there really aren’t any major geographical features to the west or south of Chicago for nearly a thousand miles (1600 kilometers).

28. Chicago’s Weather • Location effect • Once weather events start heading to Chicago, there is nothing in the geography to stop them. • This means that there are usually two to three days warning before any major weather systems hit Chicago. • This also means that any weather system that happens to head to Chicago tends to get there. • This makes Chicago weather very variable in the long term, but it also tends to be predictable in the short term.

29. Chicago’s Weather • Lake effect • As any huge mass of water does, Lake Michigan makes a dandy thermal mass. • It tends to be much warmer that the air over it in winter, and much cooler than the air in summer. • In winter, this brings lake effect snows that can drop six inches of snow on downtown while leaving the suburbs dry. • In summer, this brings the lake breeze, which can drop the temperature dramatically downtown, while it’s broiling hot in the western ‘burbs.

30. Chicago’s Weather • This also explains why NW Indiana, SE Michigan, and Buffalo, N.Y. are hit so hard by snowstorms in the winter. • As air passes over the warm lake water, it picks up moisture. • Then as it passes over the land, it cools and drops its moisture in the form of snow.

32. Freezing and Boiling • Pure water at sea level boils at 100°C and freezes at 0°C. • At higher elevations (lower atmospheric pressures) water's boiling temperature decreases. • Takes longer to boil an egg at higher altitudes • Doesn’t get high enough to cook the egg properly • If a substance is dissolved in water, the freezing point is lowered. • Spread salt on streets to prevent ice formation.

33. Biological Antifreeze • Must prevent formation of ice crystals inside cells. • Insects cells replace water with glycerol • Plants use sugars and proteins to increase solutes in the cytoplasm • Antarctic fish use glycoproteins

34. Water Vapor • Absolute humidity: actual mass of water vapor in the air • Relative humidity: % of max. water vapor for a particular temperature • Dew point: saturation point for a particular temperature

35. Air Temp. and Humidity • Warm air holds more water vapor than cold air. • This explains why indoor air is so dry in winter. • Cold air outside holds little water. • Air coming into house is dry. • Heating dries it further.

36. Absolute Humidity

37. DewPoint • If air can no longer hold water vapor without condensing, it • is saturated • has a relative humidity of 100% • has reached its dew point temperature

38. Dew Point • Temperature at which the air is completely saturated with water (i.e., RH = 100%). • At this temperature water precipitates (goes from gas to liquid or solid) and forms clouds (and dew on grass and ice tea glasses) and potentially rains/snows. • The dew point is given to indicate the amount of moisture in the air (specific humidity).

39. Dew Point • The current dew point will never be higher then the current temperature. • If the temperature is at the dew point and the temperature falls, the dew point must follow. • The higher the dew point temperature, the more moisture there is in the air. • Example: Death Valley(desert) California has low dew points, thus feels dry. • Key West Fl. has high dew points, thus feels sticky.

40. The Properties of Water • Water is the solvent, the medium and the participant in most of the chemical reactions occurring in the environment and in cells. • Water is called the universal solvent because most cellular chemicals dissolve in water. • Chemical reactions occur when the reactants (starting materials) are converted into products (end materials) • Dissolving reactants facilitates chemical reactions

41. The Properties of Water • Salt water is an aqueous solution of the salt, sodium chloride. • Water is able to dissolve sodium chloride, because of its polarity • Polar molecules are hydrophilic (water loving) because of their ability to dissolve in water

43. The Properties of Water • Salts are produced by the reactions of an acid (a substance that increases the concentration of hydrogen ions in a solution) with a base (a substance that reduces the concentration of hydrogen ions in a solution) • The pH scale is a measure of the relative amounts of these ions in a solution

44. Acids and bases • Acids are substances that dissociate and release hydrogen ions (H+). • Bases are substances that take up hydrogen ions (H+) or release hydroxide ions (OH-).

45. What is the pH scale? • A measure of hydrogen ion (H+) concentration • Working scale is between 0 and 14 with 7 being neutral • The pH scale • Low numbers (1-6) acidic • 7 is neutral • High numbers (8-14) basic

46. household bleach seawater urine tomatoes • vinegar, cola, beer • stomach acid, lemon juice • hydrochloric acid

47. The Properties of Water • Nonpolar molecules, such as oil, do not contain charged atoms • They do not mix with water • These atoms are called hydrophobic (water hating)

48. Absolute Humidity