1. Life’s Chemical Basis Chapter 2

2. 2.1 Start With Atoms  Atoms Fundamental building blocks of matter  Nucleus Positively charged protons Uncharged neutrons (except for hydrogen)  Electrons move around the nucleus Negatively charged

3. Atoms

4. electron nucleus Fig. 2.3, p. 22

7. Elements  Element A pure substance consisting of atoms with the same number of protons (atomic number)  Isotopes Atoms of the same element that differ in number of neutrons (atomic weight)

8. Periodic Table of Elements

9. Abundance of Elements

10. Hydrogen66.0% Oxygen33.0 Carbon  0.1 Nitrogen  0.1 Phosphorus  0.1 Calcium  0.1 Sodium 0.3 Potassium  0.1 Chlorine 0.3 Seawater Hydrogen 3.1% Oxygen 60.0 Carbon 0.3 Nitrogen  0.1 Phosphorus  0.1 Calcium 2.6 Sodium  0.1 Potassium 0.8 Chlorine  0.1 Earth Hydrogen62.0% Oxygen24.0 Carbon12.0 Nitrogen1.2 Phosphorus0.2 Calcium 0.2 Sodium  0.1 Potassium  0.1 Chlorine  0.1 Human Fig. 2.2, p. 21

11. 2.2 Putting Radioisotopes to Use  Radioisotopes are radioactive isotopes  They are not stable Emit particles and energy as they decay spontaneously into other elements

12. Radioactive Decay  A radioisotope decays at a constant rate into the same products Example: 14 C → 14 N  Tracer Molecule with a detectable substance attached PET scans

13. A PET Scan

14. Fig. 2.5, p. 23 portion of the patient’s body being scanned

15. detector ring inside the PET scanner Fig. 2.5, p. 23 portion of the patient’s body being scanned

16. The ring intercepts emissions from the labeled molecules Fig. 2.5, p. 23

18. Key Concepts: ATOMS AND ELEMENTS  Atoms are fundamental units of all matter  Protons, electrons, and neutrons are their building blocks  Elements are pure substances consisting of atoms that have the same number of protons  Isotopes are atoms of the same element that have different numbers of neutrons

19. 2.3 Why Electrons Matter  Electrons occupy orbitals (volumes of space) around the nucleus  Up to two electrons occupy each orbital  Shell model represents orbital energy levels as successively larger circles, or shells Used to view an atom’s electron structure

20. Shell Models

21. Electron Interactions  Atoms with unpaired electrons in their outermost shell tend to interact with other atoms They donate, accept, or share electrons to eliminate vacancies vacancy no vacancy

22. hydrogen 1p+, 1e - helium 2p+, 2e - carbon 6p+, 6e - oxygen 8p+, 8e - sodium 11p+, 11e - chlorine 17p+, 17e - Fig. 2.6, p. 24 electron neon 10p+, 10e - argon 18p+, 18e -

23. Electrical Charge  An atom with equal numbers of protons and electrons has no net charge  Ions (positive or negative) Atoms that have gained or lost electrons  Electronegativity Measure of how strongly an atom attracts electrons from other atoms

24. Ion Formation

25. Sodium atom 11p + 11e - Fig. 2.7, p. 25 no net charge Sodium ion 11p + 10e - net positive charge Chlorine atom 17p + 17e - no net charge Chlorine atom 17p + 18e - net negative charge electron loss electron gain

26. Fig. 2-7, p. 25 Sodium atom 11p + 11e - no net charge Chlorine atom 17p + 17e - no net charge Sodium ion 11p + 10e - net positive charge electron loss Chlorine atom 17p + 18e - net negative charge electron gain Stepped Art

27. Molecules and Mixtures  Chemical bond Attractive force that unites atoms into a molecule  Compounds Molecules consisting of two or more elements  Mixture Substances intermingle but don’t bond

28. Representing Molecules

29. Key Concepts: WHY ELECTRONS MATTER  Whether one atom will bond with others depends on the number and arrangement of its electrons

30. 2.4 What Happens When Atoms Interact?  Common interactions in biological molecules: Ionic bond Covalent bond Hydrogen bond

31. Ionic Bonds  Strong association between a positive ion and a negative ion (attraction of opposite charges)

32. Fig. 2.8, p. 23 Chloride ion Sodium ion A crystal of table salt is a cubic lattice of many sodium ions and chloride ions. The mutual attraction of opposite charges holds the two kinds of ions together closely in the lattice. a b

33. Covalent Bonds  Two atoms share a pair of electrons  Nonpolar covalent bond Atoms share electrons equally  Polar covalent bond Electrons are shared unequally One end slightly negative, other slightly positive Polar molecule has a separation of charge

34. Covalent Bonds

35. Fig. 2.9, p. 27 Two hydrogen atoms, each with one proton, share two electrons in a single nonpolar covalent bond. Molecular hydrogen (H—H) Two oxygen atoms, each with eight protons, share four electrons in a nonpolar double covalent bond.0 Molecular oxygen (O—O) Two hydrogen atoms each share an electron with an oxygen atom in two polar covalent bonds. The oxygen exerts a greater pull on the shared electrons, so it has a slight negative charge. Each hydrogen has a slight positive charge. Water molecule (H—O—H)

36. Hydrogen Bonds  Form between a hydrogen atom and an electronegative atom Each with separate polar covalent bonds  Are not chemical bonds Do not make atoms into molecules Individually weak Collectively stabilize structures of large molecules

37. Hydrogen Bonds

38. Fig. 2.10, p. 27 hydrogen bond water moleculeammonia molecule Two molecules interacting in one hydrogen (H) bond. a Numerous H bonds ( white dots) hold the two coiled-up strands of a DNA molecule together. Each H bond is weak, but collectively these bonds stabilize DNA’s large structure. b

39. Key Concepts: ATOMS BOND  Atoms of many elements interact by acquiring, sharing, and giving up electrons  Ionic, covalent, and hydrogen bonds are the main interactions between atoms in biological molecules

40. 2.5 Water Molecules  Water molecules are polar Form hydrogen bonds with other polar molecules Hydrophilic substances (water-loving) Hydrophobic substances (water-dreading)

41. slight negative charge on the oxygen atom The positive and negative charges balance each other; overall, the molecule carries no charge. slight positive charge on the hydrogen atoms ++ H H O Fig. 2.11, p. 28 -

42. Liquid Water: Hydrogen Bonds

43. Water’s Life-Giving Properties  Polarity gives liquid water unique properties that make life possible: Resistance to temperature changes Internal cohesion Dissolves polar and ionic substances

44. Water Temperature: From Ice to Evaporation

45. Water’s Solvent Properties  Solvents dissolve solutes (spheres of hydration)

46. Water’s Cohesion

47. Key Concepts: NO WATER, NO LIFE  Life originated in water and is adapted to its properties  Water has temperature-stabilizing effects, cohesion, and a capacity to act as a solvent for many other substances  These properties make life possible on Earth

48. 2.6 Acids and Bases  pH scale Indicates hydrogen ion (H + ) concentration of a solution Ranges from 0 (most acidic) to 14 (most basic or alkaline)  At pH 7 (neutral) H + and OH – concentrations are equal

49. A pH Scale

50. Fig. 2.14, p. 30 battery acid drain cleaner oven cleaner bleach hair remover household ammonia toothpaste hand soap milk of magnesia baking soda phosphate detergents Tums blood, tears egg white seawater pure water corn butter milk beer bread black coffee urine, tea, typical rain orange juice tomatoes, wine bananas acid rain lemon juice cola vinegar gastric fluid

51. Acids and Bases  Acids donate H + in water More H + than OH -  Bases accept H + in water More OH - than H +

52. Salts  Compounds that dissolve easily in water, and release ions other than H + and OH - Form when an acid interacts with a base Example: NaCl HCl + NaOH ↔ NaCl + H 2 O

53. Buffer System  A set of chemicals (a weak acid or base and its salt) that keeps the pH of a solution stable One donates ions, the other accepts them Example: bicarbonate (HCO 3 - ) OH - + H 2 CO 3 → HCO 3 - + H 2 O HCO 3 - + H + → H 2 CO 3

54. Functions of Buffer Systems  Buffers help maintain homeostasis  Most biological processes proceed only within a narrow pH range, usually near neutrality Acidosis Alkalosis

55. Key Concepts: HYDROGEN IONS RULE  Life is responsive to changes in the amounts of hydrogen ions and other substances dissolved in water

56. Animation: Chemical bookkeeping CLICK HERE TO PLAY

57. Animation: Electron arrangements in atoms CLICK HERE TO PLAY

58. Animation: Examples of hydrogen bonds CLICK HERE TO PLAY

59. Animation: How atoms bond CLICK HERE TO PLAY

60. Animation: Ionic bonding CLICK HERE TO PLAY

61. Animation: PET scan CLICK HERE TO PLAY

62. Animation: Shell models of common elements CLICK HERE TO PLAY

63. Animation: Spheres of hydration CLICK HERE TO PLAY

64. Animation: Structure of water CLICK HERE TO PLAY

65. Animation: The pH scale CLICK HERE TO PLAY

66. Animation: The shell model of electron distribution CLICK HERE TO PLAY