CHAPTER 2 Small Molecules: Structure and Behavior

1. CHAPTER 2Small Molecules: Structure and Behavior

2. Chapter 2: Small Molecules: Structure and Behavior Atoms: The Constituents of Matter Chemical Bonds: Linking Atoms Together Chemical Reactions: Atoms Change Partners Water: Structure and Properties

3. Chapter 2: Small Molecules: Structure and Behavior Acids, Bases, and the pH Scale The Properties of Molecules

4. Atoms: The Constituents of Matter • Matter is composed of atoms with positively charged nuclei of protons and neutrons surrounded by negatively charged electrons. 4

5. Atoms: The Constituents of Matter • Of the many elements in nature, only a few make up the bulk of living systems. Review Figure 2.1 5

6. figure 02-01.jpg 2.1 Figure 2.1

7. Atoms: The Constituents of Matter • Isotopes of an element differ in numbers of neutrons. Some are radioactive. Review Figure 2.2 7

8. figure 02-02.jpg 2.2 Figure 2.2

9. Atoms: The Constituents of Matter • Electrons are distributed in shells of orbitals containing a maximum of two. Review Figures 2.4, 2.5 9

10. figure 02-04.jpg 2.4 Figure 2.4

11. figure 02-05.jpg 2.5 Figure 2.5

12. Atoms: The Constituents of Matter • An atom can combine with other atoms to form molecules. Review Table 2.1 12

13. table 02-01.jpg Table 2.1 Table 2.1

14. Chemical Bonds: Linking Atoms Together • Covalent bonds form when two atomic nuclei share one or more pairs of electrons. • They have spatial orientations that give molecules three-dimensional shapes. Review Figures 2.6, 2.7, Table 2.2 14

15. figure 02-06.jpg 2.6 Figure 2.6

16. figure 02-07.jpg 2.7 Figure 2.7

17. table 02-02.jpg Table 2.2 Table 2.2

18. Chemical Bonds: Linking Atoms Together • Nonpolar covalent bonds form when the electronegativities of two atoms are approximately equal. • When atoms with strong electronegativity (such as oxygen) bond to atoms with weaker electronegativity (such as hydrogen), a polar covalent bond forms, in which one end is d+ and the other is d–. Review Figure 2.8, Table 2.3 18

19. figure 02-08.jpg 2.8 Figure 2.8

20. table 02-03.jpg Table 2.3 Table 2.3

21. Chemical Bonds: Linking Atoms Together • Hydrogen bonds form between a d+ hydrogen atom in one molecule and a d– nitrogen or oxygen atom in another molecule. Review Figure 2.9 21

22. figure 02-09.jpg 2.9 Figure 2.9

23. Chemical Bonds: Linking Atoms Together • Ions, electrically charged bodies, form when an atom gains or loses one or more electrons. • Ionic bonds are electrical attractions between oppositely charged ions. Review Figures 2.10, 2.11 23

24. figure 02-10.jpg 2.10 Figure 2.10

25. figure 02-11.jpg 2.11 Figure 2.11

26. Chemical Bonds: Linking Atoms Together • Nonpolar molecules do not interact directly with polar substances. • They are attracted to each other by very weak bonds called van der Waals forces. Review Figure 2.12 26

27. figure 02-12.jpg 2.12 Figure 2.12

28. Chemical Reactions: Atoms Change Partners • In chemical reactions, substances change their atomic compositions and properties. • Energy is either released or added. • Matter and energy are not created or destroyed, but change form. 28

29. Chemical Reactions: Atoms Change Partners • Combustion reactions are oxidation-reduction reactions. • Fuel is converted to carbon dioxide and water, while energy is released as heat and light. • In living cells, these reactions occur in multiple steps. Review Figure 2.13 29

30. figure 02-13.jpg 2.13 Figure 2.13

31. Water: Structure and Properties • Water’s molecular structure and capacity to form hydrogen bonds give it unusual properties significant for life. Review Figure 2.15 31

32. figure 02-15.jpg 2.15 Figure 2.15

33. Water: Structure and Properties • Cohesion of water molecules results in a high surface tension. • Water’s high heat of vaporization assures cooling when it evaporates. 33

34. Water: Structure and Properties • Solutions are substances dissolved in water. • Concentration is the amount of a given substance in a given amount of solution. • Most biological substances are dissolved at very low concentrations. 34

35. Acids, Bases, and the pH Scale • Acids are substances that donate hydrogen ions. • Bases are those that accept hydrogen ions. 35

36. Acids, Bases, and the pH Scale • The pH of a solution is the negative logarithm of the hydrogen ion concentration. • Values lower than pH 7 indicate an acidic solution. • Values above pH 7 indicate a basic solution. Review Figure 2.18 36

37. figure 02-18.jpg 2.18 Figure 2.18

38. Acids, Bases, and the pH Scale • Buffers are systems of weak acids and bases that limit the change in pH when hydrogen ions are added or removed. Review Figure 2.19 38

39. figure 02-19.jpg 2.19 Figure 2.19

40. The Properties of Molecules • Molecules vary in size, shape, reactivity, solubility, and other chemical properties. 40

41. The Properties of Molecules • Functional groups make up part of a larger molecule and have particular chemical properties. 41

42. The Properties of Molecules • The consistent chemical behavior of functional groups helps us understand the properties of the molecules that contain them. Review Figure 2.20 42

43. figure 02-20a.jpg 2.20 – Part 1 Figure 2.20 – Part 1

44. figure 02-20b.jpg 2.20 – Part 2 Figure 2.20 – Part 2

45. The Properties of Molecules • Structural and optical isomers have the same kinds and numbers of atoms, but differ in their structures and properties. Review Figure 2.21 45

46. figure 02-21.jpg 2.21 Figure 2.21