CHAPTER
4
CHAPTER
4
Study Guide
Study Guide
Key Concepts
4.1 Defining the Atom
• Democritus believed that atoms were indivisible and indestructible.
• By using experimental methods, Dalton
transformed Democritus's ideas on atoms
into a scientific theory.
• Scientists can observe individual atoms by
using instruments such as scanning tunneling microscopes.
4.3 Distinguishing Among Atoms
• Elements are different because they have different numbers of protons.
• The number of neutrons in an atom is the
difference between the mass number and
atomic number.
• Because isotopes of an element have different numbers of neutrons, they also have different mass numbers.
• To calculate the atomic mass of an element,
multiply the mass of each isotope by its natural percent abundance (expressed as a decimal), and then add the products.
• The periodic table lets you easily compare
the properties of one element (or a group of
elements) to another element (or group of
elements).
4.2 Structure of the Nuclear Atom
• Three types of subatomic particles are electrons, protons, and neutrons.
• 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.
Vocabulary
•
•
•
•
•
atom (p. 101)
atomic mass (p. 115)
atomic mass unit (amu) (p. 114)
atomic number (p. 110)
cathode ray (p. 104)
•
•
•
•
•
Dalton’s atomic theory (p. 102)
electron (p. 104)
group (p. 118)
isotopes (p. 112)
mass number (p. 111)
•
•
•
•
•
neutron (p. 106)
nucleus (p. 107)
period (p. 118)
periodic table (p. 118)
proton (p. 106)
Study Tip
Organize New Information Tell students: Use a reading strategy that you
practiced in this chapter to organize
the subject matter in a way that helps
you study. For example, if you have
trouble remembering all the new
vocabulary, try listing the new terms
and defining them in your own words.
[Interactive Textbook with ChemASAP icon]
If your class subscribes to the Interactive Textbook with ChemASAP,
your students can go online to
address an interactive version of
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with ChemASAP
Key Equation
• number of neutrons mass number atomic number
Organizing Information
Use these terms to construct a
concept map that organizes the
main ideas of this chapter.
atom
electron
isotope
Concept Map 4 Solve the
Concept map with the help of
an interactive guided tutorial.
proton
nucleus
atomic mass
neutron
mass number
atomic number
with ChemASAP
Study Guide 121
Chapter Resources
Print
• Core Teaching Resources, Chapter 4,
Practice Problems, Vocabulary Review, Quiz,
Chapter Test A, Chapter Test B
Technology
• Computer Test Bank, Chapter 4 Test
• Interactive Textbook with ChemASAP,
Chapter 4
• Virtual Chem Labs, Labs 1, 2, 3
Atomic Structure
121
CHAPTER
CHAPTER
4
Assessment
4
Assessment
Reviewing Content
45. In the Rutherford atomic model, which sub-
4.1 Defining the Atom
atomic particles are located in the nucleus?
34. What is an atom?
35. What were the limitations of Democritus’s ideas
34. The smallest particle of an element
that still has the properties of that
element.
35. Democritus’s ideas were not helpful in explaining chemical behavior
because they lacked experimental
support.
36. Dalton would agree with all four
statements because they all fit his
atomic theory.
37. The atoms are separated, joined,
and rearranged.
38. a. A beam of electrons (cathode
rays) is deflected by an electric
field toward the positively charged
plate. b. The cathode rays were
always composed of electrons
regardless of the metal used in the
electrodes or the gas used in the
cathode-ray tube.
39. repel
40. The mass of the proton and neutron are equal; protons are positively charged and neutrons are
neutral.
41. Atoms are neutral: number of protons = number of electrons. Loss of
an electron means that the number of p+ is greater than the number of e–, so the remaining particle
is positively charged.
42. The electrons were stuck in a lump
of positive charge.
43. He did not expect alpha particles
to be deflected at a large angle.
44. positive
45. protons and neutrons (Rutherford
suspected there was something in
the nucleus in addition to protons—but didn’t know them as
neutrons.)
46. It has equal numbers of protons
and electrons.
47. the number of protons in the
nucleus
48. a. 15 b. 42 c. 13 d. 48 e. 24 f. 82
49. The atomic number is the number
of protons. The mass number is the
sum of the protons and neutrons.
122 Chapter 4
about atoms?
4.3 Distinguishing Among Atoms
46. Why is an atom electrically neutral?
36. With which of these statements would John
47. What does the atomic number of each atom
Dalton have agreed in the early 1800s? For each,
explain why or why not.
a. Atoms are the smallest particles of matter.
b. The mass of an iron atom is different from the
mass of a copper atom.
c. Every atom of silver is identical to every other
atom of silver.
d. A compound is composed of atoms of two or
more different elements.
37. Use Dalton’s atomic theory to describe how
represent?
48. How many protons are in the nuclei of the fol-
lowing atoms?
phosphorus
molybdenum
aluminum
cadmium
chromium
lead
a.
b.
c.
d.
e.
f.
49. What is the difference between the mass number
atoms interact during a chemical reaction.
and the atomic number of an atom?
4.2 Structure of the Nuclear Atom
50. Complete the following table by referring to
38. What experimental evidence did Thomson have
for each statement?
a. Electrons have a negative charge.
b. Atoms of all elements contain electrons.
Figure 4.11 on page 118.
Atomic
number
Mass
number
Number
of
protons
Number
of
neutrons
Symbol
of
element
9
(d)
(g)
(j)
(a)
(e)
47
55
(b)
14
(h)
25
10
15
25
(k)
(c)
(f )
(i)
(l)
51. Name two ways that isotopes of an element
differ.
52. How can there be more than 1000 different
atoms when there are only about 100 different
elements?
39. Would you expect two electrons to attract or
repel each other?
53. What data must you know about the isotopes of
40. How do the charge and mass of a neutron
compare to the charge and mass of a proton?
41. Why does it make sense that if an atom loses
54. How is an average mass different from a
electrons, it is left with a positive charge?
weighted average mass?
42. Describe the location of the electrons in
Thomson’s “plum pudding” model of the atom.
43. How did the results of Rutherford’s gold-foil
55. What is the atomic mass of an element?
56. How are the elements arranged in the
modern periodic table?
experiment differ from his expectations?
44. What is the charge, positive or negative, of the
nucleus of every atom?
an element to calculate the atomic mass of the
element?
57. Look up the word periodic in the dictionary.
Propose a reason for the naming of the periodic
table.
122 Chapter 4
50. a. 19 b. 9 c. F d. 14 e. 29 f. Si g. 22 h. 22
i. Ti j. 25 k. 30 l. Mn
51. mass numbers, atomic masses, number
of neutrons, relative abundance
52. because of the existence of isotopes
53. which isotopes exist, their masses, and
their natural percent abundance
54. Average atomic mass is the arithmetic
mean of the isotopes. Weighted average
atomic mass considers both the mass
and the relative abundance of the
isotopes.
55. The atomic mass is the weighted average
of the masses of all the isotopes.
56. according to their atomic numbers
57. Sample answer: The table is set up so
that chemical properties of elements
recur at regular intervals.
Understanding Concepts
58. Characterize the size of an atom.
59. Compare the size and density of an atom with its
nucleus.
60. Imagine you are standing on the top of a
boron-11 nucleus. Describe the numbers and
kinds of subatomic particles you would see looking down into the nucleus, and those you would
see looking out from the nucleus.
61. What parts of Dalton's atomic theory no longer
agree with the current picture of the atom?
62. Millikan measured the quantity of charge carried
by an electron. How did he then calculate the
mass of an electron?
63. How is the number of electrons for a neutral
atom of a given element related to the atomic
number of that element?
64. How is the atomic mass of an element calculated
from isotope data?
67. Why are atoms considered the basic building
blocks of matter even though smaller particles,
such as protons and electrons, exist?
68. The following table shows some of the data
collected by Rutherford and his colleagues during their gold-foil experiment.
Angle of deflection
(degrees)
Number of deflections
5
10
15
30
45
60
75
>105
8,289,000
502,570
120,570
7800
1435
477
211
198
a. What percentage of the alpha particle deflec-
tions were 5 or less?
65. The four isotopes of lead are shown below, each
with its percent by mass abundance and the
composition of its nucleus. Using these data,
calculate the approximate atomic mass of lead.
b. What percentage of the deflections were 15
or less?
c. What percentage of the deflections were 60
or greater?
69. Using the data for nitrogen listed in Table 4.3,
82p
122n
82p
124n
1.37%
26.25%
82p
125n
82p
126n
20.82%
51.55%
calculate the weighted average atomic mass of
nitrogen. Show your work.
70. What characteristics of cathode rays led
Thomson to conclude that the rays consisted of
negatively charged particles?
71. If you know the atomic number and mass
66. Dalton’s atomic theory was not correct in every
detail. Should this be taken as a criticism of
Dalton as a scientist? Explain.
number of an atom of an element, how can you
determine the number of protons, neutrons,
and electrons in that atom?
72. What makes isotopes of the same element
chemically alike?
73. In the periodic table, what happens to the
pattern of properties within a period when you
move from one period to the next?
Assessment 123
58. very, very tiny—but larger than
protons and electrons
59. The nucleus is very small and very
dense compared with the atom.
60. 5 protons and 6 neutrons in the
nucleus; 5 electrons outside the
nucleus
61. All atoms of the same element are
not identical (isotopes). The atom is
not the smallest particle of matter.
62. He used the quantity of charge
value and the charge-to-mass ratio
measured by Thomson.
63. They are the same value.
64. The masses of isotopes in a sample
of the element are averaged, based
on relative abundance. The result is
the element’s atomic mass.
65. 207 amu
66. No; in general he proposed a valid
theory in line with the experimental evidence available to him.
67. Atoms are the smallest particle of
an element that retains the properties of that element.
68. a. 92.90% b. 99.89% c. 0.00993%
69. 147N : 14.003 amu; 99.63% 157N :
15.000 amu; 0.37%
average atomic mass = 14.01 amu
70. They were attracted to a positively
charged plate.
71. Atomic number is the same as the
number of protons and electrons;
mass number minus atomic number equals number of neutrons.
72. Because they have identical numbers of protons, they also have
identical numbers of electrons;
electrons are the subatomic particles that are responsible for chemical behavior.
73. The pattern repeats.
Atomic Structure
123
CHAPTER
CHAPTER
4
Assessment
continued
4
Assessment continued
Critical Thinking
74. The diagram below shows gold atoms being
bombarded with fast-moving alpha particles.
74. a. the nucleus of an atom; b. very
small volume; almost all the mass of
the atom; high density; positive
charge; c. electron
75. Change the metal used as a target
and account for differences in
deflection patterns.
76. The following are reasonable
hypotheses: The space in an individual atom is large relative to the
volume of the atom, but very small
relative to an object the size of a
hand. There are many layers of
atoms in a wall or a desk. The space
that exists is distributed evenly
throughout the solid, similar to the
distribution of air pockets in foam
insulation.
77. The theory must be modified and
then retested.
78. Yes—but answers will vary.
79. In a chemical change, atoms are
not created or destroyed; they are
rearranged.
¡
124 Chapter 4
carbon atoms. The density of diamond is
3.52 g/cm3. The density of graphite is 2.25 g/cm3.
In 1955, scientists successfully made diamond
from graphite. Using the relative densities, imagine what happens at the atomic level when this
change occurs. Then suggest how this synthesis
may have been accomplished.
Lithium-6 has an atomic mass of 6.015 amu;
lithium-7 has an atomic mass of 7.016 amu. The
atomic mass of lithium is 6.941 amu. What is the
percentage of naturally occurring lithium-7?
82. When the masses of the particles that make up
a. The large yellow spheres represent gold
atoms. What do the small gray spheres
represent?
b. List at least two characteristics of the small
gray spheres.
c. Which subatomic particle cannot be found in
the area represented by the gray spheres?
an atom are added together, the sum is always
larger than the actual mass of the atom. The
missing mass, called the mass defect, represents
the matter converted into energy when the
nucleus was formed from its component protons
and neutrons. Calculate the mass defect of a
chlorine-35 atom by using the data in Table 4.1.
The actual mass of a chlorine-35 atom is
5.81 1023 g.
Cumulative Review
75. How could you modify Rutherford’s experimen-
tal procedure to determine the relative sizes of
different nuclei?
76. Rutherford’s atomic theory proposed a dense
nucleus surrounded by very small electrons.
This implies that atoms are composed mainly of
empty space. If all matter is mainly empty space,
why is it impossible to walk through walls or
pass your hand through your desk?
action. What happens when new experimental
results cannot be explained by the existing
theory?
78. Do you think there are more elements left to be
discovered? Explain your answer.
79. The law of conservation of mass was introduced
in Chapter 2. Use Dalton’s atomic theory to
explain this law.
124 Chapter 4
83. Pure chemistry involves the accumulation of scientific knowledge
for its own sake. Applied chemistry
is accumulating knowledge to
attain a specific goal.
84. Scientific theory attempts to
explain why experiments give certain results. Scientific law describes
a natural phenomenon but does
not explain it.
85. a. element b. mixture
c. mixture d. mixture
86. 48 g
87. 6.38 × 107 cm3
88. 99.5 g
80. Diamond and graphite are both composed of
81. Lithium has two naturally occurring isotopes.
77. This chapter illustrates the scientific method in
80. Because diamond is more dense
than graphite, pressure could be
used to “squeeze”the carbon
atoms closer together.
81. 92.5%
82. 4 × 10–25 g
Concept Challenge
83. How does the goal of pure chemistry compare
with that of applied chemistry? (Chapter 1)
84. How does a scientific law differ from a scientific
theory? (Chapter 1)
85. Classify each as an element, a compound, or a
mixture. (Chapter 2)
a. sulfur
c. newspaper
b. salad oil
d. orange
86. Oxygen and hydrogen react explosively to form
water. In one reaction, 6 g of hydrogen combines
with oxygen to form 54 g of water. How much
oxygen was used? (Chapter 2)
87. An aquarium measures 54.0 cm 31.10 m 380.0 cm. How many cubic centimeters of water
will this aquarium hold? (Chapter 3)
88. What is the mass of 4.42 cm3 of platinum? The
density of platinum is 22.5 g/cm3. (Chapter 3)
Standardized Test Prep
Standardized Test Prep
Test-Taking Tip
Use the art to answer Question 5.
5. How many nitrogen-14 atoms (14N) would you
Connectors Sometimes two phrases in a true/
false question are connected by a word such as
because or therefore. These words imply a relationship between one part of the sentence and
another. Statements that include such words can
be false even if both parts of the statement are
true by themselves.
need to place on the right pan to balance the three
calcium-42 atoms (42Ca) on the left pan of the
“atomic balance” below? Describe the method
you used to determine your answer, including any
calculations.
6.
7.
8.
9.
Select the choice that best answers each question or
completes each statement.
1. An atom composed of 16 protons, 16 electrons,
and 16 neutrons is
a. 48
b. 16
16 S
32 Ge
c.
32
16 S
d.
1.
2.
3.
4.
5.
16
32 S
c
a
b
b
9; three 42Ca atoms have an
approximate mass of 3 × 42 =
126 amu; one 14N atom has an
approximate mass of 14 amu;
126/14 = 9 14N atoms with an
approximate mass of 126 amu.
e
false, true
true, false
true, true, correct explanation
2. Which list contains elements that fall within the
same group on the periodic table?
a. He, Ar, Xe
b. O, F, Ne
c. K, Rb, Ba
d. H, He, Li
6. Which of the following statements about the peri-
3. Which of these descriptions is incorrect?
a. proton: positive charge, in nucleus, mass
of ≈ 1 amu
b. electron: negative charge, mass of ≈ 0 amu,
in nucleus
c. neutron: mass of ≈ 1 amu, no charge
4. Thallium has two isotopes, thallium-203 and thal-
lium-205. Thallium’s atomic number is 81 and its
atomic mass is 204.38 amu. Which statement
about the thallium isotopes is true?
a. There is more thallium-203 in nature.
b. Atoms of both isotopes have 81 protons.
c. Thallium-205 atoms have fewer neutrons.
d. The most common atom of thallium has a mass
of 204.38 amu.
odic table are correct?
I. Elements are arranged in order of increasing
atomic mass.
II. A period is a horizontal row.
III. The properties of the elements within a period
vary from element to element.
a. I only
b. I and II only
c. I, II, and III
d. I and III only
e. II and III only
For each question below there are two statements. Decide whether each
statement is true or false. Then decide whether Statement II is a correct
explanation for Statement I.
Statement I
7. Every aluminum-27 atom has 27 protons
BECAUSE
Statement II
The mass number of aluminum-27 is 27.
and 27 electrons.
8. Isotopes of an element have different
BECAUSE
atomic masses.
9. An electron is repelled by a negatively
charged particle.
BECAUSE
The nuclei of an element’s isotopes contain
different numbers of protons.
An electron has a negative charge.
Standardized Test Prep 125
Atomic Structure
125