1. A Guide to the Natural World David Krogh © 2011 Pearson Education, Inc. Chapter 2 Lecture Outline Fundamental Building Blocks: Chemistry, Water, and pH Biology Fifth Edition

2. © 2011 Pearson Education, Inc. 2.1 Chemistry’s Building Block: The Atom

3. © 2011 Pearson Education, Inc. Chemistry’s Building Block: The Atom The fundamental unit of matter is the atom.

4. © 2011 Pearson Education, Inc. Protons, Neurons, and Electrons The three most important constituent parts of an atom are protons neutrons electrons

5. © 2011 Pearson Education, Inc. Protons, Neurons, and Electrons Protons and neutrons exist in the atom’s nucleus, while electrons move around the nucleus, at some distance from it.

6. © 2011 Pearson Education, Inc. Representations of Atoms Figure 2.2 electron shell nucleus Hydrogen (H)Helium (He) neutron (no charge) proton (positive charge) electron (negative charge)

7. © 2011 Pearson Education, Inc. Protons, Neurons, and Electrons Protons are positively charged. Electrons are negatively charged. Neutrons carry no charge.

8. © 2011 Pearson Education, Inc. The Element An element is any substance that cannot be reduced to any simpler set of constituent substances through chemical means. Each element is defined by the number of protons in its nucleus.

9. © 2011 Pearson Education, Inc. The Element The number of neutrons in an atom can vary independently of the number of protons. Thus, a single element can exist in various forms, called isotopes, depending on the number of neutrons it possesses.

10. © 2011 Pearson Education, Inc. The Element Figure 2.5

11. © 2011 Pearson Education, Inc. The Element Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 1: Animation

12. © 2011 Pearson Education, Inc. The Element Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 2: Exercise 1

13. © 2011 Pearson Education, Inc. The Element Animation 2.1: Structure of Atoms, Elements, Isotopes: Part 3: Exercise 2

14. © 2011 Pearson Education, Inc. The Element Protons are positively charged. Electrons are negatively charged. Neutrons carry no charge.

15. © 2011 Pearson Education, Inc. 2.2 Chemical Bonding: The Covalent Bond

16. © 2011 Pearson Education, Inc. Matter is Transformed Through Chemical Bonding Atoms can link to one another in the process of chemical bonding.

17. © 2011 Pearson Education, Inc. Covalent Bond Covalent bond: atoms share one or more electrons Ionic bond: atoms lose and accept electrons from each other

18. © 2011 Pearson Education, Inc. Covalent Bond Chemical bonding comes about as atoms “seek” their lowest energy state. An atom achieves this state when it has a filled outer electron shell.

19. © 2011 Pearson Education, Inc. Covalent Bond Hydrogen and helium require two electrons in orbit around their nuclei to have filled outer shells. Most other elements require eight electrons to have filled outer shells.

20. © 2011 Pearson Education, Inc. Electron Configurations Figure 2.6

21. © 2011 Pearson Education, Inc. Covalent Bond A molecule is a compound of a defined number of atoms in a defined spatial relationship. For example, two hydrogen atoms can link with one oxygen atom to form one water molecule.

22. © 2011 Pearson Education, Inc. Figure 2.7 Covalent Bond hydrogen (H) atom oxygen (O) atom (a) Two hydrogen atoms and one oxygen atom hydrogen (H) atom hydrogen (H) atom hydrogen (H) atom oxygen (O) atom (b) One water molecule Covalent bonds between H and O

23. © 2011 Pearson Education, Inc. Covalent Bond Atoms of different elements differ in their power to attract electrons. The term for measuring this power is electronegativity.

24. © 2011 Pearson Education, Inc. Covalent Polar and Nonpolar Bonding Through electronegativity, a molecule can take on a polarity—a difference in electrical charge at one end compared to the other.

25. © 2011 Pearson Education, Inc. Covalent Polar and Nonpolar Bonding Covalent chemical bonds can be polar or nonpolar. A polar covalent bond exists when shared electrons are not shared equally among atoms in a molecule, due to electronegativity differences.

26. © 2011 Pearson Education, Inc. Polar and Nonpolar Covalent Bonding Figure 2.8 (a) Polar water molecule slight negative charge slight positive charge polar (b) Nonpolar methane molecule nonpolar because charges are symmetric

27. © 2011 Pearson Education, Inc. 2.3 The Ionic Bond

28. © 2011 Pearson Education, Inc. Ionic Bonding Two atoms will undergo a process of ionization when the electronegativity differences between them are great enough that one atom loses one or more electrons to the other. This process creates ions: atoms whose number of electrons differs from their number of protons.

29. © 2011 Pearson Education, Inc. Ionic Bonding The charge differences that result from ionization can produce an electrostatic attraction between ions. This attraction is an ionic bond. When atoms of two or more elements bond together ionically, the result is an ionic compound.

30. © 2011 Pearson Education, Inc. Figure 2.9 (a) Initial instability Sodium has but a single electron in its outer shell, while chlorine has seven, meaning it lacks only a single electron to have a completed outer shell. (b) Electron transfer When these two atoms come together, sodium loses its third-shell electron to chlorine, in the process becoming a sodium ion with a net positive charge (because it now has more protons than electrons). Having gained an electron, the chlorine atom becomes a chloride ion, with a net negative charge (because it has more electrons than protons). sodium atom (Na)chlorine atom (CI) electron transfer sodium ion (Na + ) ionic compound (Na + Cl – ) chloride ion (CI – ) (c) Ionic attraction The sodium and chloride ions are now attracted to each other because they are oppositely charged. salt crystals (d) Compound formation The result of this electrostatic attraction, involving many sodium and chloride ions, is a sodium chloride crystal (NaCl), better known as table salt.

31. © 2011 Pearson Education, Inc. 2.4 The Hydrogen Bond

32. © 2011 Pearson Education, Inc. Hydrogen Bonding Hydrogen bonding links an already covalently bonded hydrogen atom with an electronegative atom.

33. © 2011 Pearson Education, Inc. Hydrogen Bonding In water, a hydrogen atom of one water molecule will form a hydrogen bond with an unshared oxygen electron of a neighboring water molecule.

34. © 2011 Pearson Education, Inc. Hydrogen Bonding Figure 2.10

35. © 2011 Pearson Education, Inc. Hydrogen Bonding Animation 2.2: Chemical Bonding

36. © 2011 Pearson Education, Inc. 2.5 Three-Dimensional Shapes in Molecules

37. © 2011 Pearson Education, Inc. Three-Dimensional Shape The three-dimensional molecular shape is important in biology because it determines the capacity molecules have to bind with one another.

38. © 2011 Pearson Education, Inc. signal molecules (aroma from bread) bad fit, scent is not smelled good fit, scent is smelled receptor molecules cells of nasal passage signal to brain Figure 2.12

39. © 2011 Pearson Education, Inc. 2.6 Water and Life

40. © 2011 Pearson Education, Inc. Water and Life Water has several qualities that have strongly affected life on Earth.

41. © 2011 Pearson Education, Inc. Water Is a Major Player in Many of Life’s Processes A solution is a homogeneous mixture of two or more kinds of molecules, atoms, or ions. The compound dissolved in solution is the solute; the compound doing the dissolving is the solvent.

42. © 2011 Pearson Education, Inc. Water’s Power as a Solvent (a) Attraction (b) Separation (c) Dispersion Sodium chloride’s positively charged sodium ions (Na + ) are attracted to water's negatively charged oxygen atoms, while its negatively charged chloride ions (Cl – ) are attracted to water's positively charged hydrogen atoms. Pulled from the crystal and separated from each other by this attraction, sodium and chloride ions become surrounded by water molecules. This process of separating sodium and chloride ions repeats until both types of ions are evenly dispersed, making this an aqueous solution. Sodium and chloride ions dissolved in water (solvent) sodium chloride (solute) Figure 2.14

43. © 2011 Pearson Education, Inc. Water Is a Major Player in Many of Life’s Processes Water is a powerful solvent, with the ability to dissolve more compounds in greater amounts than any other liquid.

44. © 2011 Pearson Education, Inc. Water’s Structure Gives It Many Unusual Properties Because water’s solid form (ice) is less dense than its liquid form, bodies of water in colder climates do not freeze solid in winter. Allows life to flourish under the ice.

45. © 2011 Pearson Education, Inc. ice In ice, the maximum number of hydrogen bonds form, causing the molecules to be spread far apart. liquid water In liquid water, hydrogen bonds constantly break and re-form, enabling a more dense spacing than in ice. Figure 2.15

46. © 2011 Pearson Education, Inc. Water’s Structure Gives It Many Unusual Properties Water has a great capacity to absorb and retain heat. Because of this, the oceans act as heat buffers for the Earth, thus stabilizing Earth’s temperature.

47. © 2011 Pearson Education, Inc. Water’s Structure Gives It Many Unusual Properties Water has a high degree of cohesion, which allows water to be drawn up through plants, via evaporation, in one continuous column, from roots through leaves.

48. © 2011 Pearson Education, Inc. Hydrophobic and Hydrophilic Some compounds do not interact with water. Hydrocarbons such as petroleum are examples of such hydrophobic compounds. Water cannot break down hydrophobic compounds, which is why oil and water don’t mix.

49. © 2011 Pearson Education, Inc. Hydrophobic and Hydrophilic Figure 2.17

50. © 2011 Pearson Education, Inc. Hydrophobic and Hydrophilic Compounds that interact with water are polar or carry an electric charge and are called hydrophilic compounds.

51. © 2011 Pearson Education, Inc. 2.7 Acids and Bases

52. © 2011 Pearson Education, Inc. Acids and Bases An acid is any substance that yields hydrogen ions when put in aqueous solution. A base is any substance that accepts hydrogen ions in solution.

53. © 2011 Pearson Education, Inc. Acids and Bases A base added to an acidic solution makes that solution less acidic. An acid added to a basic solution makes that solution less basic.

54. © 2011 Pearson Education, Inc. Figure 2.18 (a) Starting with pure water Pure water is a “neutral” substance in terms of its pH levels. pure water (H 2 O) HCI (b) Making water more acidic Hydrochloric acid (HCl), poured into the water, dissociates into H + and Cl – ions. With a higher concentration of H + ions in it, the water moves toward the acidic end of the pH scale. (c) Making water more basic An equal concentration of sodium hydroxide, poured into water, dissociates into Na + and OH – ions, moving the water toward the basic end of the scale. (d) Combining acidic and basic solutions When the acid and base solutions are poured together, the OH – ions from (c) accept the H + ions from (b), forming water and keeping the solution at a neutral pH. neutralized solution NaOH base acid

55. © 2011 Pearson Education, Inc. Acids and Bases The concentration of hydrogen ions that a given solution has determines how basic or acidic that solution is. The pH scale measures acidity. This scale runs from 0 to 14, with 0 most acidic,14 the most basic, and 7 neutral.

56. © 2011 Pearson Education, Inc. Figure 2.19 Acids and Bases

57. © 2011 Pearson Education, Inc. Acids and Bases The pH scale is logarithmic. A substance with a pH of 9 is 10 times as basic as a substance with a pH of 8

58. © 2011 Pearson Education, Inc. Acids and Bases Living things function best in a near-neutral pH, although some systems in living things have different pH requirements.