1. Copyright © 2009 Pearson Education, Inc.. Lectures by Gregory Ahearn University of North Florida Chapter 2 Atoms, Molecules, and Life

2. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms?  Elements: substances that can neither be broken down nor converted to other substances (e.g., carbon)

3. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms?  Atoms: basic structural unit of matter; made up of subatomic particles Atomic nucleus (central part of the atom) Protons (positive charge) Neutrons (neutral charge) Electrons (negative charge)  Atomic number: the number of protons in the nucleus Is unique for each element 92 different elements have been described.

4. Copyright © 2009 Pearson Education Inc. e-e- p+p+ n n e-e- p+p+ p+p+ e-e- atomic nucleus (a) Hydrogen (H) (b) Helium (He) 2.1 What Are Atoms?  Hydrogen and helium have the simplest atomic structure. Hydrogen has one proton and one electron. Helium has two protons, two neutrons, and two electrons. Fig. 2-1

5. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms?  Atoms of the same element with different numbers of neutrons are called isotopes of the element.  Some isotopes spontaneously break apart, forming different kinds of atoms and releasing energy in the process.  Such isotopes are radioactive.  Example: radioactive uranium isotopes decay and form lead in the process

6. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms? Animation—Atomic Structure PLAY

7. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms?  Electron shells: electrons orbit around atomic nuclei at specific distances, called electron shells.  Different atoms have different electron shells: The inner shell only has two electrons. The second shell holds up to eight electrons. Additional shells hold up to eight electrons.

8. Copyright © 2009 Pearson Education Inc. Carbon (C) Oxygen (O) Phosphorus (P) Calcium (Ca) O C P Ca 8e-8e- 8e-8e- 2e-2e- 20p + 20n 2e-2e- 4e-4e- 6e-6e- 2e-2e- 2e-2e- 6p+6p+ 8p+8p+ 6n6n8n8n 5e-5e- 8e-8e- 2e-2e- 15p + 16n 2.1 What Are Atoms?  The first four atomic electron shells Carbon (C) Oxygen (O) Phosphorus (P) Calcium (Ca) Fig. 2-2

9. Copyright © 2009 Pearson Education Inc. 2.1 What Are Atoms?  Electrons can move from electron shell to electron shell. Electrons move from an inner to an outer shell when absorbing energy. Electrons move from an outer shell to an inner shell when releasing energy. Fig. 2-3 The energy boosts the electron to a higher-energy shell The electron drops back into lower-energy shell, releasing energy as light energy light 1 2 3 An electron absorbs energy – + + – + –

10. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Molecules: two or more atoms of one or more elements held together by interactions among their outermost electron shells Atoms interact with one another according to two basic principles: An inert atom will not react with other atoms when its outermost electron shell is completely full or empty. A reactive atom will react with other atoms when its outermost electron shell is only partially full.

11. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Atoms combine with each other to fill outer electron shells (e.g. hydrogen and oxygen have unfilled outer electron shells, and thus, can combine to form the water molecule).  The water molecule, with a filled outer electron shell, is more stable than either the hydrogen or oxygen atoms that gave rise to it.  The results of losing, gaining, or sharing electrons are chemical bonds—attractive forces that hold atoms together in molecules.

12. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Animation—Biologically Important Atoms PLAY

13. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  A molecule may be depicted in different ways. Fig. 2-4 (a) All bonds shown (b) Bonds within common groups omitted (c) Carbons and their attached hydrogens omitted (d) Overall shape depicted CH 3 CH 2 OH CH H H C H H C H H COH H H

14. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Types of bonds Ionic bonds: formed by passing an electron from one atom to another One partner becomes positive, the other negative, and they attract one another. Na + + Cl – becomes NaCl (sodium chloride) Positively or negatively charged atoms are called ions.

15. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Charged atoms interact to form ionic bonds. Positively charged atoms Negatively charged atoms Fig. 2-5 Electron transferred Attraction between opposite charges Sodium ion (+)Chloride ion (–) Sodium atom (neutral) Chlorine atom (neutral) 11p + 11n 17p + 18n 11p + 11n 17p + 18n Na + Cl - Na + Cl - Na + Cl - Neutral atoms (a) An ionic compound: NaCl (c) Ions (b) – – – – – –– – – – – – – – – –– – – – – – – – – – –– – – – – – – – – – – – – – – – –– – – – – – – – – – – –

16. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Animation—Ionic Bonds PLAY

17. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Types of bonds (continued) Covalent bonds: bond between two atoms that share electrons in their outer electron shell For example, an H atom can become stable by sharing its electron with another H atom, forming H 2 gas.

18. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Covalent bonds produce either nonpolar or polar molecules. Nonpolar molecule: atoms in a molecule equally share electrons that spend equal time around each atom, producing a nonpolar covalent bond

19. Copyright © 2009 Pearson Education Inc. Nonpolar covalent bonding in hydrogen (uncharged) Electrons spend equal time near each nucleus Same charge on both nuclei (a) + + – – 2.2 How Do Atoms Form Molecules?  Nonpolar covalent bonding in hydrogen Fig. 2-6a

20. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Covalent bonds produce either nonpolar or polar molecules (continued). Polar molecules: atoms in a bond unequally share electrons, producing a polar covalent bond One atom in the bond has a more positive charge in the nucleus, and so attracts electrons more strongly, becoming the negative pole of the molecule. The atom in the bond that has a less positive charge in the nucleus gives up electrons, becoming the positive pole of the molecule.

21. Copyright © 2009 Pearson Education Inc. Polar covalent bonding in water (oxygen: slightly negative) (hydrogens: slightly positive) Larger positive charge Electrons spend more time near the larger nucleus Smaller positive charge (+) (–) (b) 8p+8p+ 8n8n + + – – – – – – – – – – 2.2 How Do Atoms Form Molecules?  Polar covalent bonding in water Fig. 2-6b

22. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Animation—Covalent Bonds PLAY

23. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Types of bonds (continued) Hydrogen bonds: weak electrical attraction between positive and negative parts of polar molecules Example: the negative charge of oxygen atoms in water molecules attract the positive charge of hydrogen atoms in other water molecules

24. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?  Hydrogen bonds Fig. 2-7 hydrogen bonds O (–) H (+) O (–) H (+)

25. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules? Animation—Introducing Water’s Properties PLAY

26. Copyright © 2009 Pearson Education Inc. 2.2 How Do Atoms Form Molecules?

27. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  Water interacts with many other molecules. Oxygen released by plants during photosynthesis comes from water. Water is used by animals to digest food. Water is produced in chemical reactions that produce proteins, fats, and sugars.

28. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  Many molecules dissolve easily in water. Water is an excellent solvent, capable of dissolving a wide range of substances because of its positive and negative poles.  NaCl dropped into H 2 O The positive end of H 2 O is attracted to Cl –. The negative end of H 2 O is attracted to Na +. These attractions tend to push apart the components of the original salt.

29. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  Water as a solvent Fig. 2-8 Cl – O H H Na +

30. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Animation—Solvent PLAY

31. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  Water molecules tend to stick together. Surface tension: water tends to resist being broken Cohesion: water molecules stick together Fig. 2-9

32. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Animation—High Cohesion PLAY

33. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  Water can form ions. Water spontaneously becomes H + and OH –. Acid solutions have a lot of H + (protons). Alkaline solutions have a lot of OH – (hydroxyl ions). A base is a substance that combines with H +, reducing their numbers. pH measures the relative amount of H + and OH – in a solution.

34. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  A water molecule is ionized. Fig. 2-10 hydrogen ion (H + ) hydroxide ion (OH – ) water (H 2 O) + (+)(–) O HH O H H

35. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  pH measures acidity. Acids have a pH below 7. Bases have a pH above 7. Neutral solutions have a pH of 7. Buffers are substances that maintain a constant pH in a solution.

36. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life?  The pH scale Fig. 2-11 H + concentration in moles/liter increasingly acidicincreasingly basic pH value 01234 56789 10 111213 14 neutral (H + = OH – ) (H + > OH – ) (H + < OH – ) 10 0 10 –1 10 –2 10 –3 10 –4 10 –5 10 –6 10 –7 10 –8 10 –9 10 –10 10 –11 10 –12 10 –13 10 –14 1 molar hydrochloric acid (HCl) stomach acid (2) lemon juice (2.3) vinegar, cola (3.0) orange (3.5) tomatoes beer (4.1) black coffee (5.0) normal rain (5.6) urine (5.7) water from faucet milk (6.4) pure water (7.0) blood, sweat (7.4) seawater (7.8–8.3)baking soda (8.4) toothpaste (9.9) household ammonia (11.9) washing soda (12) phosphate detergents chlorine bleach (12.6) oven cleaner (13.0) drain cleaner (14.0) 1 molar sodium hydroxide (NaOH)

37. Copyright © 2009 Pearson Education Inc. 2.3 Why Is Water So Important To Life? Animation—pH Scale PLAY

38. Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life?  Carbon can combine with other atoms in many ways to form a huge number of different molecules.  This is possible because carbon has four electrons in its outermost shell, leaving room for four more electrons from other atoms.  Therefore, carbon can form many bonds with other atoms.

39. Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life?  The great variety of substances found in nature is therefore constructed from a limited pool of atoms.  Organic molecules have a carbon skeleton and some hydrogen atoms.  Much of the diversity of organic molecules is due to the presence of functional groups.

40. Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life?

41. Copyright © 2009 Pearson Education Inc. 2.4 Why Is Carbon So Important To Life? Animation—Functional Groups PLAY

42. Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart?  Dehydration synthesis The construction of large molecules yields water. Small molecules are joined together to form large molecules. During the joining of small molecules, water is released. This water-releasing reaction is called dehydration synthesis.

43. Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart?  Dehydration synthesis Fig. 2-12a dehydration synthesis Dehydration synthesis O HH O HO O OH HO + (a) H

44. Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart?  Hydrolysis reactions During the breakdown of large molecules, covalent bonds are broken, separating the subunits

45. Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart?  Hydrolysis Fig. 2-12b hydrolysis Hydrolysis O H H O OH HO + O OH (b) H

46. Copyright © 2009 Pearson Education Inc. 2.5 How Are Biological Molecules Joined Together Or Broken Apart? Animation—Dehydration Synthesis and Hydrolysis PLAY

47. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates?  Carbohydrates are molecules composed of carbon, hydrogen, and oxygen in the ratio of 1:2:1.  They can be small single sugar molecules or long chains of single sugar molecules strung together.

48. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates?  A simple sugar Fig. 2-13 Glucose, linear form Glucose, ring form (a)(b) H H CH 2 OH HO OH O H H H 23 564 1 HHHH H H H H HH H H OOOOO O CCC C C C

49. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates?  Monosaccharide: a carbohydrate consisting of one sugar molecule  Disaccharide: two sugars linked together  Polysaccharide: three or more sugars linked together

50. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates?  Simple sugars, such as glucose, provide important energy sources for organisms.  Sucrose, such as table sugar, is a disaccharide containing one glucose molecule attached to a fructose molecule.

51. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates?  Manufacture of a disaccharide Fig. 2-14 glucosefructosesucrose dehydration synthesis O HO O HOCH 2 OH HO CH 2 OH H H OH H H H O HO O CH 2 OH H H OH H H H H H H HO CH 2 OH H HOCH 2 H H H HO CH 2 OH O OH O + O HH

52. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates? Animation—Carbohydrates PLAY

53. Copyright © 2009 Pearson Education Inc. 2.6 What Are Carbohydrates?  Some complex sugars, such as cellulose, provide support for cells or even the entire bodies of organisms.  Complex sugars are made by the dehydration synthesis of simple sugars.  Cellulose is the most abundant organic molecule on Earth because it provides support for plants in fields and forests.  Cellulose is made of long chains of glucose subunits.