1. Chapter 4: Atomic Structure
4.1 Defining the Atom

2. Connecting to Your World
4.1
Connecting to Your World
The lab technician shown here is using a magnifying lens to examine a bacterial culture in a petri dish. When scientists cannot see the details of what they study, they try to obtain experimental data that help fill in the picture.

3. Early Models of the Atom
4.1
Early Models of the Atom
An atom is the smallest particle of an element that retains its identity in a chemical reaction.
Philosophers and scientists have proposed many ideas on the structure of atoms.

4. Early Models of the Atom
4.1
Early Models of the Atom
Democritus’s Atomic Philosophy
Democritus

5. Early Models of the Atom
4.1
Early Models of the Atom
Democritus believed that atoms were indivisible and indestructible.
Democritus’s ideas were limited because they didn’t explain chemical behavior and they lacked experimental support.

6. Dalton’s Atomic Theory
4.1
Dalton’s Atomic Theory
All elements are composed of tiny indivisible particles called atoms.
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?

7. Dalton’s Atomic Theory
4.1
Dalton’s Atomic Theory
Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?

8. Dalton’s Atomic Theory
4.1
Dalton’s Atomic Theory
Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?

9. Dalton’s Atomic Theory
4.1
Dalton’s Atomic Theory
Chemical reactions occur when atoms are separated, joined, or rearranged. 
According to Dalton’s atomic theory, an element is composed of only one kind of atom, and a compound is composed of particles that are chemical combinations of different kinds of atoms. a) Atoms of element A are identical. b) Atoms of element B are identical, but differ from those of element A. c) Atoms of elements A and B can physically mix together. d) Atoms of elements A and B can chemically combine to form a compound. Interpreting Diagrams How does a mixture of atoms of different elements differ from a compound?
Scientists used a scanning tunneling microscope to generate this image of iron atoms, shown in blue. The radius of this circle of atoms is just 7.13 × 10-9 m.

10. 4.1
Sizing up the Atom
Despite their small size, individual atoms are observable with instruments such as scanning tunneling microscopes.

11. 4.1
Sizing up the Atom
Iron Atoms Seen Through a Scanning Tunneling Microscope

12. Connecting Concepts
Scientific Methods
Explain why the ideas on atoms proposed by Dalton constitute a theory, while the ideas proposed by Democritus do not.

13. 4.1 Section Quiz
1. The ancient Greek philosopher credited with suggesting all matter is made of indivisible atoms is
a) Plato.
b) Aristotle.
c) Democritus.
d) Socrates.
ANS: C PTS: 1 REF: p. 101 OBJ: 4.1.1

14. 4.1 Section Quiz
2. Dalton's atomic theory improved earlier atomic theory by
a) teaching that all matter is composed of tiny particles called atoms.
b) theorizing that all atoms of the same element are identical.
c) using experimental methods to establish a scientific theory.
d) not relating atoms to chemical change.
ANS: C PTS: 1 REF: p. 102 OBJ: 4.1.2

15. 3. Individual atoms are observable with a) the naked eye.
4.1 Section Quiz
3. Individual atoms are observable with
a) the naked eye.
b) a magnifying glass.
c) a light microscope.
d) a scanning tunneling microscope.
ANS: D PTS: 1 REF: p. 103 OBJ: 4.1.3

16. 4.2 Structure of the Nuclear Atom

17. Connecting to Your World
4.2
Connecting to Your World
Cathode-ray tubes are found in TVs, computer monitors, and many other devices with electronic displays.

18. 4.2
Subatomic Particles
Three kinds of subatomic particles are electrons, protons, and neutrons.

19. 4.2
Subatomic Particles
Electrons
In 1897, the English physicist J. J. Thomson (1856–1940) discovered the electron. Electrons are negatively charged subatomic particles.

20. 4.2
Subatomic Particles
Thomson performed experiments that involved passing electric current through gases at low pressure. The result was a glowing beam, or cathode ray, that traveled from the cathode to the anode.

21. Cathode Ray Tube
In a cathode-ray tube, electrons travel as a ray from the cathode (-) to the anode (+). A television tube is a specialized type of cathode-ray tube.

22. Subatomic Particles A cathode ray is deflected by a magnet. 4.2
Thomson examined two ways that a cathode ray can be deflected: a) by using a magnet, and b) by using electrically charged plates. Inferring If a cathode ray is attracted to a positively charged plate, what can you infer about the charge of the particles that make up the cathode ray?

23. 4.2
Subatomic Particles
A cathode ray is deflected by electrically charged plates.
In a cathode-ray tube, electrons travel as a ray from the cathode (-) to the anode (+). A television tube is a specialized type of cathode-ray tube.

24. 4.2
Subatomic Particles
Thomson concluded that a cathode ray is a stream of electrons. Electrons are parts of the atoms of all elements.

25. Such positively charged subatomic particles are called protons.
4.2
Subatomic Particles
Protons and Neutrons
In 1886, Eugen Goldstein (1850–1930) observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. He concluded that they were composed of positive particles.
Such positively charged subatomic particles are called protons.

26. 4.2
Subatomic Particles
In 1932, the English physicist James Chadwick (1891–1974) confirmed the existence of yet another subatomic particle: the neutron.
Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton.

27. 4.2
Subatomic Particles

28. 4.2
The Atomic Nucleus
J.J. Thompson and others supposed the atom was filled with positively charged material and the electrons were evenly distributed throughout – plum pudding model.
This model of the atom turned out to be short-lived, however, due to the work of Ernest Rutherford (1871–1937).

29. Figure 3.3: Plum Pudding model of an atom - Thomson

30. The Atomic Nucleus Ernest Rutherford’s Portrait 4.2
Born in New Zealand, Ernest Rutherford was awarded the Nobel Prize for Chemistry in His portrait appears on the New Zealand $100 bill.

31. 4.2
The Atomic Nucleus
Rutherford’s Gold-Foil Experiment
In 1911, Rutherford and his coworkers at the University of Manchester, England, directed a narrow beam of alpha particles at a very thin sheet of gold foil.

32. The Atomic Nucleus 4.2 Rutherford’s Gold-Foil Experiment
Rutherford’s gold-foil experiment yielded evidence of the atomic nucleus. a) Rutherford and his coworkers aimed a beam of alpha particles at a sheet of gold foil surrounded by a fluorescent screen. Most of the particles passed through the foil with no deflection at all. A few particles were greatly deflected. b) Rutherford concluded that most of the alpha particles pass through the gold foil because the atom is mostly empty space. The mass and positive charge are concentrated in a small region of the atom. Rutherford called this region the nucleus. Particles that approach the nucleus closely are greatly deflected.

33. Figure 3.5: Rutherford’s experiment

34. The Atomic Nucleus Alpha particles scatter from the gold foil. 4.2
Rutherford’s gold-foil experiment yielded evidence of the atomic nucleus. a) Rutherford and his coworkers aimed a beam of alpha particles at a sheet of gold foil surrounded by a fluorescent screen. Most of the particles passed through the foil with no deflection at all. A few particles were greatly deflected. b) Rutherford concluded that most of the alpha particles pass through the gold foil because the atom is mostly empty space. The mass and positive charge are concentrated in a small region of the atom. Rutherford called this region the nucleus. Particles that approach the nucleus closely are greatly deflected.

35. The Rutherford Atomic Model
4.2
The Rutherford Atomic Model
Rutherford concluded that the atom is mostly empty space. All the positive charge and almost all of the mass are concentrated in a small region called the nucleus.
The nucleus is the tiny central core of an atom and is composed of protons and neutrons.

36. 4.2
The Atomic Nucleus
In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are distributed around the nucleus and occupy almost all the volume of the atom.

37. Writing Activity Explanatory Paragraph
Write a paragraph explaining how Rutherford’s gold foil experiment yielded new evidence about atomic structure. Hint: First describe the setup of the experiment. Then explain how Rutherford interpreted his experimental data.
Read p.109: Electron Microscopy

38. 1. Which of the following is NOT an example of a subatomic particle?
4.2 Section Quiz
1. Which of the following is NOT an example of a subatomic particle?
a) proton
b) molecule
c) electron
d) neutron
ANS: B PTS: 1 REF: p. 104 OBJ: 4.2.1

39. 2. The nucleus of an atom consists of a) electrons only.
4.2 Section Quiz
2. The nucleus of an atom consists of
a) electrons only.
b) protons only.
c) protons and neutrons.
d) electrons and neutrons.
ANS: C PTS: 1 REF: p. 107 OBJ: 4.2.2

40. 3. Most of the volume of the atom is occupied by the a) electrons.
4.2 Section Quiz
3. Most of the volume of the atom is occupied by the
a) electrons.
b) neutrons.
c) protons and neutrons.
d) protons.
ANS: A PTS: 1 REF: p. 108 OBJ: 4.2.2

41. 4.3 Distinguishing Among Atoms

42. Connecting to Your World
4.3
Connecting to Your World
Just as apples come in different varieties, a chemical element can come in different “varieties” called isotopes.

43. 4.3
Atomic Number
Elements are different because they contain different numbers of protons.
The atomic number of an element is the number of protons in the nucleus of an atom of that element.

44. 4.3
Atomic Number

46. for Conceptual Problem 4.1

47. 4.3
Mass Number
The total number of protons and neutrons in an atom is called the mass number.
The number of neutrons in an atom is the difference between the mass number and atomic number.

48. Mass Number Au is the chemical symbol for gold. 4.3
Au is the chemical symbol for gold. Applying Concepts How many electrons does a gold atom have?

49. Sample Problem 4.1

50. 4.1

51. for Sample Problem 4.1
18. Express the composition of each atom in shorthand form.
a) carbon-12
b) fluorine -19
c) beryllium - 9

52. 4.3
Isotopes
Isotopes are atoms that have the same number of protons but different numbers of neutrons.
Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.

53. 4.3
Isotopes
Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons.
Neon-20, neon-21, and neon-22 are three isotopes of neon, a gaseous element used in lighted signs. Comparing and Contrasting How are these isotopes different? How are they similar?

55. for Conceptual Problem 4.2

56. Tell protons, neutrons and electrons for:
6027Co
3717Cl
23892U
4) Carbon-12
5) Carbon -14
6) Strontium-90
7) Mercury-201

57. Examples Carbon- 13 Xenon-131 Sodium-24 Oxygen- 15 #p #n #e Z A

58. 4.3
Atomic Mass
It is useful to to compare the relative masses of atoms to a standard reference isotope. Carbon-12 is the standard reference isotope. Cabon-12 has a mass of exactly 12 atomic mass units.
An atomic mass unit (amu) is defined as one twelfth of the mass of a carbon-12 atom.

59. Some Elements and Their Isotopes
4.3
Some Elements and Their Isotopes

60. 4.3
Atomic Mass
The atomic mass of an element is a weighted average mass of the atoms in a naturally occurring sample of the element.
A weighted average mass reflects both the mass and the relative abundance of the isotopes as they occur in nature.

61. Weighted Average Mass of a Chlorine Atom
4.3
Weighted Average Mass of a Chlorine Atom
Chlorine is a reactive element used to disinfect swimming pools. Chlorine occurs as two isotopes: chlorine-35 and chlorine-37. Because there is more chlorine-35 than chlorine-37, the atomic mass of chlorine, amu, is closer to 35 than to 37. Evaluating How does a weighted average differ from an arithmetic mean?

64. for Conceptual Problem 4.3

65. 4.3
Atomic Mass
To calculate the atomic mass of an element, multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.

66. Atomic Mass For example, carbon has two stable isotopes:
4.3
Atomic Mass
For example, carbon has two stable isotopes:
Carbon-12, which has a natural abundance of 98.89%, and
Carbon-13, which has a natural abundance of 1.11%.

67. Sample Problem 4.2

68. 4.2

69. 4.2

70. Practice Problem 23
The element copper has naturally occurring isotopes with mass numbers of 63 and 65. The relative abundance and atomic masses are 69.2% for mass = amu, and 30.8% for mass = amu. Calculate the average atomic mass for copper.

71. for Sample Problem 4.2

72. The Periodic Table—A Preview
4.3
The Periodic Table—A Preview
A periodic table is an arrangement of elements in which the elements are separated into groups based on a set of repeating properties.
A periodic table allows you to easily compare the properties of one element (or a group of elements) to another element (or group of elements).

73. The Periodic Table—A Preview
4.3
The Periodic Table—A Preview
Elements are arranged in the modern periodic table in order of atomic number. Interpreting Diagrams How many elements are in Period 2? In Group 2A?

74. The Periodic Table—A Preview
4.3
The Periodic Table—A Preview
Each horizontal row of the periodic table is called a period.
Within a given period, the properties of the elements vary as you move across it from element to element.

75. A Period

76. The Periodic Table—A Preview
4.3
The Periodic Table—A Preview
Each vertical column of the periodic table is called a group, or family.
Elements within a group have similar chemical and physical properties.

77. 4.3
A Group or Family

78. Elements Handbook
Elements Within You
Read page R5 of the Elements Handbook. Identify the five most abundant elements in the human body, and locate them on the periodic table.

79. 4.3 Section Quiz 1. Isotopes of an element have
a) the same mass number.
b) different atomic numbers.
c) the same number of protons but different numbers of neutrons.
d) the same number of protons but different numbers of electrons.
ANS: C PTS: 1 REF: p. 112 OBJ: 4.3.1

80. 2. How many neutrons are in sulfur-33? a) 16 neutrons b) 33 neutrons
4.3 Section Quiz
2. How many neutrons are in sulfur-33?
a) 16 neutrons
b) 33 neutrons
c) 17 neutrons
d) neutrons
ANS: C PTS: 1 REF: p. 111 OBJ: 4.3.2

81. 4.3 Section Quiz
3. If sulfur contained 90.0% sulfur-32 and 10.0% sulfur-34, its atomic mass would be
a) 32.2 amu.
b) 32.4 amu.
c) 33.0 amu.
d) 35.4 amu.
ANS: A PTS: 1 REF: p. 116 OBJ: 4.3.3