1. Molecules of Life
Chapter 2
Part 1

2. 2.1 Impacts/Issues Fear of Frying
All living things consist of the same kinds of molecules, but small differences in the ways they are put together have big effects on health
Artificial trans fats found in manufactured and fast foods raise cholesterol and increase risk of atherosclerosis, heart attack, and diabetes

3. Video: Fear of frying

4. Fear of Frying
Trans fats are made by adding hydrogen atoms to liquid vegetable oils

5. trans fatty acid Figure 2.1
Trans fats. Left, the particular arrangement of hydrogen atoms around two carbon atoms (yellow box) makes a trans fat very unhealthy as a food. Right, french fries and other fast foods are often cooked with trans fats.
Fig. 2-1, p. 20

6. 2.2 Start With Atoms All substances consist of atoms Atom
Fundamental building-block particle of matter
Life’s unique characteristics start with the properties of different atoms

7. Subatomic Particles and Their Charge
Atoms consist of electrons moving around a nucleus of protons and neutrons
Electron (e-)
Negatively charged subatomic particle that occupies orbitals around the atomic nucleus
Charge
Electrical property of some subatomic particles
Opposite charges attract; like charges repel

8. Subatomic Particles in the Nucleus
Core of an atom, occupied by protons and neutrons
Proton (p+)
Positively charged subatomic particle found in the nucleus of all atoms
Neutron
Uncharged subatomic particle found in the atomic nucleus

9. An Atom

10. an atom
Figure 2.2
Atoms consist of electrons moving around a core, or nucleus, of protons and neutrons. Models cannot show what atoms really look like. Electrons zoom around in fuzzy, three-dimensional spaces about 10,000 times bigger than a nucleus.
Fig. 2-2a, p. 21

11. Elements: Different Types of Atoms
Atoms differ in numbers of subatomic particles
Element
A pure substance that consists only of atoms with the same number of protons
Atomic number
Number of protons in the atomic nucleus
Determines the element

12. Elements in Living Things
The proportions of different elements differ between living and nonliving things
Some atoms, such as carbon, are found in greater proportions in molecules made only by living things – the molecules of life

13. Same Elements, Different Forms
Isotopes
Forms of an element that differ in the number of neutrons their atoms carry
Changes the mass number, but not the charge
Mass number
Total number of protons and neutrons in the nucleus of an element’s atoms

14. Radioactive Isotopes Radioisotope Radioactive decay
Isotope with an unstable nucleus, such as carbon 14 (14C)
Radioactive decay
Process by which atoms of a radioisotope spontaneously emit energy and subatomic particles when their nucleus disintegrates

15. Carbon 14: A Radioisotope
Most carbon atoms have 6 protons and 6 neutrons (12C)
Carbon 14 (14C) is a radioisotope with six protons and eight neutrons
When 14C decays, one neutron splits into a proton and an electron, and the atom becomes a different element – nitrogen 14 (14N)

16. Radioactive Tracers
Researchers introduce radioisotope tracers into living organisms to study the way they move through a system
Tracers
Molecules with a detectable substance attached, often a radioisotope
Used in research and clinical testing

17. Why Electrons Matter
Electrons travel around the nucleus in different orbitals (shells) – atoms with vacancies in their outer shells tend to interact with other atoms
Atoms get rid of vacancies by gaining or losing electrons, or sharing electrons with other atoms
Shell model
Model of electron distribution in an atom

18. Shell Models

19. Figure 2.3: Animated!
Shell models. Each circle (shell) represents all orbitals at one energy level. Atoms with vacancies in their outermost shell can interact with other atoms.
Fig. 2-3 (top), p. 22

20. Figure 2.3: Animated!
Shell models. Each circle (shell) represents all orbitals at one energy level. Atoms with vacancies in their outermost shell can interact with other atoms.
Fig. 2-3 (a-c), p. 22

21. 1 proton 1 2 1 electron first shell hydrogen (H) helium (He) 6 8 10
second shell
carbon (C)
oxygen (O)
neon (Ne)
Figure 2.3: Animated!
Shell models. Each circle (shell) represents all orbitals at one energy level. Atoms with vacancies in their outermost shell can interact with other atoms. 11 17 18
third shell
sodium (Na)
chlorine (Cl)
argon (Ar)
Fig. 2-3 (a-c), p. 22

22. 1 proton 1 2 1 electron first shell hydrogen (H) helium (He)
A) The first shell corresponds to the first energy level, and it can hold up to 2 electrons. Hydrogen has one proton, so it has one vacancy. A helium atom has 2 protons, and no vacancies. The number of protons in each shell model is shown. 6 8 10
second shell
carbon (C)
oxygen (O)
neon (Ne)
B) The second shell corresponds to the second energy level, and it can hold up to 8 electrons. Carbon has 6 protons, so its first shell is full. Its second shell has 4 electrons, and four vacancies.
Oxygen has 8 protons and two vacancies. Neon has 10 protons and no vacancies. 11 17 18
third shell
sodium (Na)
chlorine (Cl)
argon (Ar)
C) The third shell, which corresponds to the third energy level, can hold up to 8 electrons, for a total of 18. A sodium atom has 11 protons, so its first two
shells are full; the third shell has one electron. Thus, sodium has seven vacancies. Chlorine has 17 protons and one vacancy. Argon has 18 protons and no vacancies.
Figure 2.3: Animated!
Shell models. Each circle (shell) represents all orbitals at one energy level. Atoms with vacancies in their outermost shell can interact with other atoms.
Stepped Art
Fig. 2-3 (a-c), p. 22

23. Animation: Shell models of common elements

24. Ions
The negative charge of an electron balances the positive charge of a proton in the nucleus
Changing the number of electrons may fill its outer shell, but changes the charge of the atom
Ion
Atom that carries a charge because it has an unequal number of protons and electrons

25. Ion Formation

26. electron gain Chlorine atom 17p+ 17 17e– charge: 0 Chloride ion 17
electron loss
Sodium atom
11p+
Figure 2.4: Animated!
Ion formation.
(A) A sodium atom becomes a positively charged sodium ion (Na+) when it loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies.
(B) A chlorine atom becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. 11
11e–
charge: 0
Sodium ion 11
11p+
10e–
charge: +1
Fig. 2-4, p. 23

27. Figure 2.4: Animated!
Ion formation.
(A) A sodium atom becomes a positively charged sodium ion (Na+) when it loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies.
(B) A chlorine atom becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell.
Fig. 2-4a, p. 23

28. electron gain Chlorine atom 17p+ 17 17e– charge: 0 Chloride ion 17p+
Figure 2.4: Animated!
Ion formation.
(A) A sodium atom becomes a positively charged sodium ion (Na+) when it loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies.
(B) A chlorine atom becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell.
17p+ 17
18e–
charge: –1
Fig. 2-4a, p. 23

29. Figure 2.4: Animated!
Ion formation.
(A) A sodium atom becomes a positively charged sodium ion (Na+) when it loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies.
(B) A chlorine atom becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell.
Fig. 2-4b, p. 23

30. electron loss Sodium atom 11p+ 11 11e– charge: 0 Sodium ion 11 11p+
Figure 2.4: Animated!
Ion formation.
(A) A sodium atom becomes a positively charged sodium ion (Na+) when it loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies.
(B) A chlorine atom becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell. 11
11p+
10e–
charge: +1
Fig. 2-4b, p. 23

31. electron gain Chlorine atom 17p+ 17 17e– charge: 0 Chloride ion 17
electron loss
Sodium ion
11p+ 11
charge: +1
10e–
Sodium atom 11
11p+
11e–
charge: 0
Figure 2.4: Animated!
Ion formation.
(A) A sodium atom becomes a positively charged sodium ion (Na+) when it loses the electron in its third shell. The atom’s full second shell is now its outermost, so it has no vacancies.
(B) A chlorine atom becomes a negatively charged chloride ion (Cl–) when it gains an electron and fills the vacancy in its third, outermost shell.
Stepped Art
Fig. 2-4, p. 23

32. Animation: How atoms bond

33. Animation: PET scan

34. Animation: The shell model of electron distribution

35. Animation: Subatomic particles

36. Animation: Atomic number, mass number

37. Animation: Electron arrangements in atoms

38. Animation: Isotopes of hydrogen

39. Video: ABC News: Nuclear Energy

40. Animation: Electron distribution

41. 2.3 From Atoms to Molecules
Atoms can also fill their vacancies by sharing electrons with other atoms
A chemical bond forms when the electrons of two atoms interact
Chemical bond
An attractive force that arises between two atoms when their electrons interact

42. From Atoms to Molecules
Group of two or more atoms joined by chemical bonds
Compound
Type of molecule that has atoms of more than one element

43. Referring to a Molecule

44. Same Materials, Different Results

45. Animation: Building blocks of life

46. Ionic Bonds and Covalent Bonds
Depending on the atoms, a chemical bond may be ionic or covalent
Ionic bond
A strong mutual attraction formed between ions of opposite charge
Covalent bond
Two atoms sharing a pair of electrons

47. An Ionic Bond: Sodium Chloride

48. ionic bond 11 17
sodium ion (Na+)
chloride ion (Cl–)
p. 24

49. Covalent Bonds
Molecular hydrogen (H—H) and molecular oxygen (O=O)

50. molecular hydrogen (H2)1 1
molecular hydrogen (H2) 8 8
molecular oxygen (O2)
p. 24

51. Polarity
A covalent bond is nonpolar if electrons are shared equally, and polar if the sharing is unequal
Polarity
Any separation of charge into distinct positive and negative regions

52. Polar and Nonpolar Covalent Bonds
Having an even distribution of charge
When atoms in a covalent bond share electrons equally, the bond is nonpolar
Polar
Having an uneven distribution of charge
When the atoms share electrons unequally, the bond is polar

53. Importance of Polar Molecules
A water molecule (H-O-H) has two polar covalent bonds – the oxygen is slightly negative and the hydrogens are slightly positive – which allows water to form hydrogen bonds

54. p. 25

55. 1 8 1
water (H2O)
p. 25

56. Hydrogen Bonds Hydrogen bond
Attraction that forms between a covalently bonded hydrogen atom and another atom taking part in a separate covalent bond

57. hydrogen bond
p. 25

58. Importance of Hydrogen Bonds
Hydrogen bonds form and break more easily than covalent or ionic bonds – they do not form molecules
Hydrogen bonds impart unique properties to substances such as water, and hold molecules such as DNA in their characteristic shapes

59. Animation: Ionic bonding

60. Animation: Examples of hydrogen bonds

61. Video: ABC News: Fuel Cell Vehicles

62. Animation: Sucrose synthesis

63. Animation: Covalent bonds

64. 2.4 Water
All living organisms are mostly water, and all chemical reactions of life are carried out in water
Hydrogen bonds between water molecules give water unique properties that make life possible
Capacity to dissolve many substances
Cohesion (surface tension)
Temperature stability

65. Polarity and the Unique Properties of Water

66. Figure 2.7: Animated!
Water. (A) Polarity of a water molecule: Each of the hydrogen atoms has a slight positive charge, and the oxygen atom has a slight negative charge. (B) The many hydrogen bonds (dashed lines) that keep water molecules clustered together impart special properties to liquid water. (C) Visible effect of cohesion: a wasp drinking (not sinking). Cohesion imparts surface tension to liquid water, which means that the surface of liquid water behaves a bit like a sheet of elastic.
Fig. 2-7a, p. 26

67. slight negative charge
Figure 2.7: Animated!
Water. (A) Polarity of a water molecule: Each of the hydrogen atoms has a slight positive charge, and the oxygen atom has a slight negative charge. (B) The many hydrogen bonds (dashed lines) that keep water molecules clustered together impart special properties to liquid water. (C) Visible effect of cohesion: a wasp drinking (not sinking). Cohesion imparts surface tension to liquid water, which means that the surface of liquid water behaves a bit like a sheet of elastic.
slight positive charge
slight positive charge
Fig. 2-7a, p. 26

68. Figure 2.7: Animated!
Water. (A) Polarity of a water molecule: Each of the hydrogen atoms has a slight positive charge, and the oxygen atom has a slight negative charge. (B) The many hydrogen bonds (dashed lines) that keep water molecules clustered together impart special properties to liquid water. (C) Visible effect of cohesion: a wasp drinking (not sinking). Cohesion imparts surface tension to liquid water, which means that the surface of liquid water behaves a bit like a sheet of elastic.
Fig. 2-7b, p. 26

69. Figure 2.7: Animated!
Water. (A) Polarity of a water molecule: Each of the hydrogen atoms has a slight positive charge, and the oxygen atom has a slight negative charge. (B) The many hydrogen bonds (dashed lines) that keep water molecules clustered together impart special properties to liquid water. (C) Visible effect of cohesion: a wasp drinking (not sinking). Cohesion imparts surface tension to liquid water, which means that the surface of liquid water behaves a bit like a sheet of elastic.
Fig. 2-7c, p. 26

70. Animation: Structure of water

71. Water and Solutions
Polar water molecules hydrogen-bond to other polar (hydrophilic) substances, and repel nonpolar (hydrophobic) substances
Hydrophilic (water-loving)
A substance that dissolves easily in water
Hydrophobic (water-dreading)
A substance that resists dissolving in water

72. Water and Solutions Water is an excellent solvent Solvent Solute
Liquid that can dissolve other substances
Solute
A dissolved substance

73. Water and Solutions
Salts, sugars, and many polar molecules dissolve easily in water
Salt
Compound that dissolves easily in water and releases ions other than H+ and OH-
Example: sodium chloride (NaCl)

74. Water and Solutions
Water molecules surround the atoms of an ionic solid and pull them apart, dissolving it

75. Animation: Spheres of hydration

76. Temperature Stability
Temperature stability is an important part of homeostasis
Water absorbs more heat than other liquids before temperature rises
Hydrogen bonds hold ice together in a rigid pattern that makes ice float
Temperature
Measure of molecular motion

77. Cohesion
Cohesion helps sustain multicelled bodies and resists evaporation
Cohesion
Tendency of water molecules to stick together
Evaporation
Transition of liquid to gas
Absorbs heat energy (cooling effect)

78. 2.5 Acids and Bases
Water molecules separate into hydrogen ions (H+) and hydroxide ions (OH-) pH
A measure of the number of hydrogen ions (H+) in a solution
The more hydrogen ions, the lower the pH
Pure water has neutral pH (pH=7)
Number of H+ ions = OH- ions

79. Acids and Bases Acid Base
Substance that releases hydrogen ions in water
pH less than 7
Base
Substance that releases hydroxide ions (accepts hydrogen ions) in water
pH greater than 7

80. A pH Scale

81. — 0 battery acid — 1 gastric fluid — 2 acid rain lemon juice cola
more acidic
vinegar
— 3
orange juice
tomatoes, wine
— 4
bananas
beer
bread
— 5
black coffee
urine, tea, typical rain
— 6
corn
butter
milk
— 7
pure water
blood, tears
egg white
— 8
seawater
baking soda
— 9
detergents
Tums
Figure 2.9: Animated!
A pH scale. Here, red dots signify hydrogen ions (H+) and blue dots signify hydroxyl ions (OH–). Also shown are approximate pH values for some common solutions. This pH scale ranges from 0 (most acidic) to 14 (most basic). A change of one unit on the scale corresponds to a tenfold change in the amount of H+ ions.
Figure It Out: What is the approximate pH of cola?
Answer: 2.5.
toothpaste
— 10
hand soap
milk of magnesia
more basic
— 11
household ammonia
— 12
hair remover
bleach
— 13
oven cleaner
— 14
drain cleaner
Fig. 2-9, p. 27

82. Animation: The pH scale

83. Acid Rain
Sulfur dioxide and other airborne pollutants dissolve in water vapor to form acid rain

84. Buffer Systems
Most molecules of life work only within a narrow range of pH – essential for homeostasis
Buffers keep solutions in cells and tissues within a consistent range of pH
Buffer
Set of chemicals that can keep the pH of a solution stable by alternately donating and accepting ions that contribute to pH

85. CO2 and the Bicarbonate Buffer System
CO2 forms carbonic acid in water
CO2 + H2O → H2CO3 (carbonic acid)
Bicarbonate buffer system
Excess H+ combines with bicarbonate
H+ + HCO3- (bicarbonate) ↔ H2CO3

86. Video: ABC News: Bottle Backlash

87. Video: ABC News: Water Use

88. Video: ABC News: Water Wars

89. 3D Animation: Dissolution