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Copyright © 2005 Pearson Prentice Hall, Inc.
Chapter 2
• Atoms, Molecules, and Life
Copyright © 2005 Pearson Prentice Hall, Inc.
2.1 What Are Atoms?
• 2.1.1 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)
nn
Hydrogen (H)
electronshell
nucleus
e-
p+ p+
p+
e-
e-
Hydrogen (H)
electronshell
nucleus
e-
p+
Helium (He)
nn
e-
p+
p+
e-
Copyright © 2005 Pearson Prentice Hall, Inc.
2.1 What Are Atoms?
– 2.1.1.1 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)CaOC P
4e– 6e–
5e–
2e–
8e–
8e–
8e–
2e– 2e–
2e–
2e–
6p+ 8p+ 15p+ 20p+6n 8n 16n 20n
Copyright © 2005 Pearson Prentice Hall, Inc.
2.2 How Do Atoms Interact to Form Molecules?
• 2.2.1 Atoms Interact with Other Atoms When There Are Vacancies in Their Outermost Electron Shells
• 2.2.2 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–
Cl–
Na+
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?
• 2.2.3 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 H2O)
Hydrogen (H–H or H2)
Oxygen (O=O or O2)
(slightly negative)
(slightly positive)
8p+8n
8p+8n
8p+8n
Copyright © 2005 Pearson Prentice Hall, Inc.
2.2 How Do Atoms Interact to Form Molecules?
– 2.2.3.1 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?
– 2.2.3.2 Electron Sharing Determines Whether a Covalent Bond Is Nonpolar or Polar
– 2.2.3.3 Free Radicals Are Highly Reactive and Can Damage Cells
• 2.2.4 Hydrogen Bonds Are Weaker Electrical Attractions Between or Within Molecules with Polar Covalent Bonds– Figure 2.5 Hydrogen bonds (p. 28)
O(–)
H(+)
hydrogrenbonds
H(+)
H(+)
H(+)
O(–)
Copyright © 2005 Pearson Prentice Hall, Inc.
2.3 Why Is Water So Important to Life?
• 2.3.1 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–
Cl–
Na+
Na+
Na+
H
H
H
H
O
O–
hydrogen bond
hydroxylgroup
glucose
water
Copyright © 2005 Pearson Prentice Hall, Inc.
2.3 Why Is Water So Important to Life?
• 2.3.2 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(H2O)
+(+)
(–)
H H H
H
Copyright © 2005 Pearson Prentice Hall, Inc.
2.3 Why Is Water So Important to Life?
• 2.3.3 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 hydrochloricacid (HCI)
stomach acidlime 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)salivablood, sweat (7.4)
seawater (7.8–8.3)
baking soda
phosphate detergentschlorine bleachmilk of magnesia
household ammoniasome detergents(without phosphates)
washing soda
oven cleaner
1-molar sodiumhydroxide (NaOH)
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
pHvalueH+ concentration
(moles/liter)100
10–1
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–)
incr
easi
ngly
aci
dic
(H+ >
OH
– )in
cre
asi
ng
ly b
asi
c (
H+ <
OH
– )
1-molar hydrochloricacid (HCI)
stomach acidlime 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)
0
1
2
3
4
5
6
pHvalue
H+ concentration(moles/liter)
100
10–1
10–2
10–3
10–1
10–5
10–6
incr
easi
ngly
aci
dic
(H
+ >
OH
– )
incr
easi
ngly
bas
ic (
H+ <
OH
–)
pure water (7.0)alivablood, sweat (7.4)
seawater (7.8–8.3)
baking soda
phosphate detergentschlorine bleachmilk of magnesia
household ammoniasome detergents(without phosphates)
washing soda
oven cleaner
1-molar sodiumhydroxide (NaOH)
7
8
9
10
11
12
13
14
10–7
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?
– 2.3.3.1 A Buffer Helps Maintain a Solution at a Relatively Constant pH
• 2.3.4 Water Moderates the Effects of Temperature Changes
• 2.3.5 Water Forms an Unusual Solid: Ice– Figure E2.2 Chocolate (p. 33)
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