Copyright © 2005 Pearson Prentice Hall, Inc. Chapter 2 Atoms, Molecules, and Life

Copyright © 2005 Pearson Prentice Hall, Inc. 2.1 What Are Atoms? Atoms, the Basic Structural Units of Matter, Are Composed of Still Smaller Particles –Figure 2.1 Atomic models (p. 22) –Table 2.1 Common Elements Important in Living Organisms (p. 22) –Figure E2.1 How positron emission tomography works (p.23)

Helium (He) n n Hydrogen (H) electron shell nucleus e-e- p+p+ p+p+ p+p+ e-e- e-e-

Hydrogen (H) electron shell nucleus e-e- p+p+

Helium (He) n n e-e- p+p+ p+p+ e-e-

Copyright © 2005 Pearson Prentice Hall, Inc. 2.1 What Are Atoms? – Electrons Orbit the Nucleus at Fixed Distances, Forming Electron Shells That Correspond to Different Energy Levels Figure 2.2 Electron shells in atoms (p. 24)

Carbon (C)Oxygen (O) Phosphorus (P) Calcium (Ca) Ca O C P 4e–4e– 6e–6e– 5e–5e– 2e–2e– 8e–8e– 8e–8e– 8e–8e– 2e–2e– 2e–2e– 2e–2e– 2e–2e– 6p+6p+ 8p+8p+ 15p + 20p + 6n6n8n8n 16n20n

Copyright © 2005 Pearson Prentice Hall, Inc. 2.2 How Do Atoms Interact to Form Molecules? Atoms Interact with Other Atoms When There Are Vacancies in Their Outermost Electron Shells Charged Atoms Called Ions Interact to Form Ionic Bonds –Figure 2.3 (Hide/Reveal) The formation of ions and ionic bonds (p. 25)

Sodium atom (neutral) Na 17p + 11p + 11n 11p + 11n Chlorine atom (neutral) 18n 17p + 18n Cl Sodium ion (+) Chloride ion (–) Cl – Na + An ionic compound: NaCl

Sodium atom (neutral) Na 17p + 11p + 11n Chlorine atom (neutral) 18n Cl

11p + 11n 17p + 18n Sodium ion (+) Chloride ion (–) Cl – Na +

Cl – Na + An ionic compound: NaCl

Copyright © 2005 Pearson Prentice Hall, Inc. 2.2 How Do Atoms Interact to Form Molecules? Uncharged Atoms Can Become Stable by Sharing Electrons, Forming Covalent Bonds –Figure 2.4 Covalent bonds involve shared electrons (p. 26) –Table 2.2 Chemical Bonds (p. 26)

Nonpolar covalent bonding Polar covalent bonding Water (H–O–H or H 2 O) Hydrogen (H–H or H 2 ) Oxygen (O=O or O 2 ) (slightly negative) (slightly positive) 8p+8p+ 8n8n 8p+8p+ 8n8n 8p+8p+ 8n8n

Copyright © 2005 Pearson Prentice Hall, Inc. 2.2 How Do Atoms Interact to Form Molecules? – Most Biological Molecules Utilize Covalent Bonding Unnumbered Figure 3 Bonding Patterns of Atoms Commonly Found in Biological Molecules (p. 27) Table 2.3 Bonding Patterns of Atoms Commonly Found in Biological Molecules (p. 27)

Copyright © 2005 Pearson Prentice Hall, Inc. 2.2 How Do Atoms Interact to Form Molecules? – Electron Sharing Determines Whether a Covalent Bond Is Nonpolar or Polar – Free Radicals Are Highly Reactive and Can Damage Cells Hydrogen Bonds Are Weaker Electrical Attractions Between or Within Molecules with Polar Covalent Bonds –Figure 2.5 Hydrogen bonds (p. 28)

O (–) H (+) hydrogren bonds H (+) H (+) H (+) O (–)

Copyright © 2005 Pearson Prentice Hall, Inc. 2.3 Why Is Water So Important to Life? Water Interacts with Many Other Molecules –Figure 2.6 Water as a solvent (p. 29) –Figure 2.7 Water dissolves many biological molecules (p. 29)

Cl – Na + H H H H O O–O–

hydrogen bond hydroxyl group glucose water

Copyright © 2005 Pearson Prentice Hall, Inc. 2.3 Why Is Water So Important to Life? Water Molecules Tend to Stick Together –Figure 2.8 Cohesion among water molecules (p. 30) –Unnumbered Figure 1 Ionization of Water (p. 30)

O O hydrogen ion (H + ) hydroxide ion (OH – ) water (H 2 O) + (+) (–) HHH H

Copyright © 2005 Pearson Prentice Hall, Inc. 2.3 Why Is Water So Important to Life? Water-Based Solutions Can Be Acidic, Basic, or Neutral –Figure 2.9 The pH scale (p. 31) –Unnumbered Figure 2 Comparison of liquid and solid phases of water (p. 32)

1-molar hydrochloric acid (HCI) stomach acid lime juice lemon juice "acid rain" (2.5–5.5) vinegar, cola, orange juice, tomatoes beer black coffee, tea normal rain (5.6) urine (5.7) pure water (7.0) saliva blood, sweat (7.4) seawater (7.8 – 8.3) baking soda phosphate detergents chlorine bleach milk of magnesia household ammonia some detergents (without phosphates) washing soda oven cleaner 1-molar sodium hydroxide (NaOH) pH value H + concentration (moles/liter) –1 10 –2 10 –3 10 –4 10 –5 10 –6 10 –7 –6 –7 –8 –9 –10 –11 –12 –13 –14 10 –8 10 –9 10 –10 10 –11 10 –12 10 –13 10 –14 neutral (H + = OH – ) increasingly acidic (H + > OH – ) increasingly basic (H + < OH – )

1-molar hydrochloric acid (HCI) stomach acid lime juice lemon juice "acid rain" (2.5–5.5) vinegar, cola, orange juice, tomatoes beer black coffee, tea normal rain (5.6) urine (5.7) pH value H + concentration (moles/liter) –1 10 –2 10 –3 10 –1 10 –5 10 –6 increasingly acidic (H + > OH – )

increasingly basic (H + < OH – ) pure water (7.0) aliva blood, sweat (7.4) seawater (7.8–8.3) baking soda phosphate detergents chlorine bleach milk of magnesia household ammonia some detergents (without phosphates) washing soda oven cleaner 1-molar sodium hydroxide (NaOH) –7 10 –8 10 –9 10 –10 10 –11 10 –12 10 –13 10 –14 neutral (H + = OH – )

Copyright © 2005 Pearson Prentice Hall, Inc. 2.3 Why Is Water So Important to Life? – A Buffer Helps Maintain a Solution at a Relatively Constant pH Water Moderates the Effects of Temperature Changes Water Forms an Unusual Solid: Ice –Figure E2.2 Chocolate (p. 33)