General Chemistry

1. General Chemistry • Element • composed of atoms • Nucleus • protons (+) and neutrons (0) • Electrons (-)

2. Figure 5.1

4. General Chemistry • Molecule • a group of atoms held together by chemical bonds

5. General Chemistry • Bonds • covalent bonds form when electrons are shared

7. General Chemistry • Bonds • ionic bonds form by attraction between particles with opposite charges

9. Water • H2O • covalent bonds hold the 2 hydrogen & 1 oxygen together

10. Electron (–1 unit of charge) 105° 2 – Nucleus (+1 unit of charge) Two hydrogen atoms... share their electrons with one oxygen atom... to form a water molecule held together by covalent bonds... which acts as if it has negative and positive ends. Stepped Art Fig. 6-1, p. 122

11. Figure 5.2

12. Water • Water molecules have an uneven distribution of charge = polar or dipolar • H positive • O negative

13. Water • Polar nature of water leads to: • attraction of other water molecules= cohesion • attraction of other charged or polar molecules=adhesion

14. Water • Hydrogen Bonds • form between hydrogen of one water molecule and the oxygen of another

15. Figure 5.3

16. Hydrogen Bonds In An Ice Crystal Fig. 6-5, p. 125

17. Fig. 6-4, p. 125

18. Figure 5.5

19. Water • Universal solvent • Solution • solvent • solute

20. Fig. 6-11, p. 129

21. Figure 5.4

22. Seawater • 96.5% water & 3.5% solutes • solutes change properties of water

23. Table 5.2

24. Figure 5.15

25. Salinity • total concentration of all dissolved inorganic solids • average = 3.5% or 35 ppt (35o/oo)

26. Sources of Ocean’s salts • weathering of surface rocks (stream run-off) • sodium, magnesium, calcium • Outgassing (volcanoes and hydrothermal vents) • chlorine, carbon dioxide, sulfur, hydrogen

27. The Ocean is in Chemical Equilibrium • Overall amount of dissolved salts in the ocean is nearly constant • Additions of salts are balance by the removal of salts

28. Figure 5.19

29. Dissolved Gases • Needed by organisms • Gases dissolve more readily in cold water • major gases • nitrogen 48% • oxygen 36% • carbon dioxide 15%

30. Nitrogen • Needed for proteins • bacteria must “fix” the nitrogen • most recycled among organisms

31. Oxygen • More abundant in atmosphere (100x) than in ocean • photosynthesis & diffusion add oxygen • respiration by organisms uses up oxygen

32. Carbon Dioxide • More abundant in ocean (about 60x) than in atmosphere • respiration by organisms adds carbon dioxide • Photosynthesis uses up carbon dioxide

33. Fig. 6-16, p. 133

34. Acid-Base Balance • Use pH scale to measure acidity or alkalinity • pH scales measure concentration of hydrogen ions (H+) • pH scale is logarithmic…a change of 1 pH unit represents a ten-fold difference in H+ concentrations • Low pH = acidic, high pH = basic

35. Figure 5.20

36. Fig. 6-17, p. 134

37. Acid-Base Balance • Seawater pH is about 8, slightly alkaline • CO2 dissolves in water to form carbonic acid (H2CO3) • Carbonic acid breaks down to H+, bicarbonate ion (HCO3-)and carbonate ion (CO32-) • this acts to buffer seawater from large swings in pH as acids and bases are introduced in the ocean

38. Figure 5.21

39. Acid-Base Balance • Excess CO2 can lower pH • This occurs in cold, deep water where respiration occurs but no photosynthesis • This low pH of 7.5 can dissolve calcium carbonate sediments • Global change is causing ocean acidification

40. Fig. 6-16, p. 133