Download 4.1 Studying Atoms

Section 4.1
4.1 Studying Atoms
1 FOCUS
Objectives
4.1.1
4.1.2
4.1.3
Describe ancient Greek models
of matter.
List the main points of Dalton’s
atomic theory and describe his
evidence for the existence of
atoms.
Explain how Thomson and
Rutherford used data from
experiments to produce their
atomic models.
Key Concepts
Reading Strategy
What was Dalton’s theory
of the structure of matter?
What contributions did
Thomson and Rutherford
make to the development
of atomic theory?
Vocabulary
◆
nucleus
L2
Figure 1 Aristotle thought that
all substances were built up from
only four elements—earth, air,
fire, and water. These elements
were a combination of four
qualities—hot, cold, dry, and wet.
Fire was a combination of hot and
dry. Water was a combination of
cold and wet.
Water
d
Earth
Co
l
Air
et
W
2 INSTRUCT
Fire
y
Dr
H
ot
L2
a. Dalton b. Indivisible, solid spheres
c. Thomson d. Negative charges evenly
scattered through a positively charged
mass of matter (plum pudding model)
e. Deflection of alpha particles passing
through gold foil
Ancient Greek
Models of Atoms
Use Visuals
L1
Figure 1 Have students examine the
diagram in Figure 1 that lists the
qualities of each of Aristotle’s four
elements. Ask, What qualities did
Aristotle use to describe air? (Air is a
combination of hot and wet.) What
element was a combination of dry
and cold? (Earth) Is “wet and cold”
an accurate description of water?
(Wet describes water, but water isn’t
always cold.)
Visual
100 Chapter 4
Evidence
Model
a.
?
Ratio of masses
in compounds
b.
?
c.
?
Deflected beam
d.
?
e.
Positive, dense
nucleus
?
S
Latin Plural Forms Explain that the
word nucleus comes from a Latin word
meaning “kernel.” Explain that a kernel
is a grain or seed. Ask students to discuss
how the definition of the term nucleus
relates to its Latin origin. (Like the kernel
of a nut, the nucleus is a small, massive
center of the atom.) Remind students that
the plural of the word nucleus is nuclei.
Reading Strategy
Scientist
Rutherford
Reading Focus
Build Vocabulary
Summarizing Copy the
table. As you read,
complete the table about
atomic models.
100
tudying the structure of atoms is a little like studying wind. Because
you cannot see air, you must use indirect evidence to tell the direction
of the wind. You might notice which way fallen leaves move as they are
pushed by the wind, and infer that the leaves and wind are moving in
the same direction.
Atoms pose a similar problem because they are extremely small.
Even with a microscope, scientists cannot see the structure of an atom.
In this chapter, you will find out how John Dalton, J. J. Thomson,
Ernest Rutherford, Niels Bohr, and other scientists used evidence from
experiments to develop models of atoms.
Ancient Greek Models of Atoms
If you cut a piece of aluminum foil in half, you have two smaller pieces
of the same shiny, flexible substance. You could cut the pieces again and
again. Can you keep dividing the aluminum into smaller pieces? Greek
philosophers debated a similar question about 2500 years ago.
The philosopher Democritus believed that all matter consisted of
extremely small particles that could not be divided. He called these
particles atoms from the Greek word atomos, which means “uncut” or
“indivisible.” He thought there were different types of atoms with specific sets of properties. The atoms in liquids, for example, were round
and smooth, but the atoms in solids were rough and prickly.
Aristotle did not think there was a limit to the number of times
matter could be divided. Figure 1 shows the model Aristotle used to
describe matter. For many centuries, most people accepted Aristotle’s
views on the structure of matter. But by the 1800s, scientists had
enough data from experiments to support an atomic model of matter.
Chapter 4
Section Resources
Print
• Reading and Study Workbook With
Math Support, Section 4.1
• Transparencies, Chapter Pretest and
Section 4.1
Technology
• Interactive Textbook, Section 4.1
• Presentation Pro CD-ROM, Chapter Pretest
and Section 4.1
• Go Online, NSTA SciLinks, Atomic theory
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Page 101
Dalton’s Atomic
Theory
Dalton’s Atomic Theory
John Dalton was born in England in 1766. He was a teacher who spent
his spare time doing scientific experiments. Because of his interest in
predicting the weather, Dalton studied the behavior of gases in air.
Based on the way gases exert pressure, Dalton correctly concluded that
a gas consists of individual particles.
Build Science Skills
Evaluating As students read Chapter 4,
have them evaluate what portions of
Dalton’s model were accurate and what
portions needed to be revised. (Dalton
did not discuss subatomic particles,
which are smaller components of atoms.
Atoms of the same element can have
different masses.)
Logical
Evidence for Atoms Dalton gathered evidence for the existence
of atoms by measuring the masses of elements that combine when
compounds form. He noticed that all compounds have something in
common. No matter how large or small the sample, the ratio of the
masses of the elements in the compound is always the same. In other
words, compounds have a fixed composition.
For example, when magnesium burns, as shown in Figure 2, it
combines with oxygen. The product of this change is a white solid
called magnesium oxide. A 100-gram sample of magnesium combines
with 65.8 grams of oxygen. A 10-gram sample of magnesium combines with 6.58 grams of oxygen. The ratio of the mass of magnesium
to the mass of oxygen is constant in magnesium oxide.
Figure 2 Magnesium reacts with
oxygen to form the compound
magnesium oxide. The ratio of
magnesium to oxygen, by mass, in
magnesium oxide is always about
3 : 2. Observing What color is
magnesium oxide?
Dalton’s Theory Dalton developed a theory to explain why the
elements in a compound always join in the same way.
Dalton proposed the theory that all matter is made up of individual particles
called atoms, which cannot be divided. The main points of Dalton’s
theory are as follows.
■
All elements are composed of atoms.
■
All atoms of the same element have the same mass, and atoms of
different elements have different masses.
■
Compounds contain atoms of more than one element.
■
In a particular compound, atoms of different elements always
combine in the same way.
L2
Figure 3 Dalton made these
wooden spheres to represent the
atoms of different elements.
In the model of atoms based on Dalton’s theory, the elements
are pictured as solid spheres like those in Figure 3. Each type of
atom is represented by a tiny, solid sphere with a different mass.
Recall that a theory must explain the data from many experiments. Because Dalton’s atomic theory met that goal, the theory
became widely accepted. Over time, scientists found that not all
of Dalton’s ideas about atoms were completely correct. But this did
not cause later scientists to discard the atomic theory. Instead, they
revised the theory to take into account new discoveries.
L2
Many students have trouble differentiating compounds from mixtures.
Remind students that Dalton noticed
that the ratio of masses of elements
in a compound is always the same.
Compounds are distinguished from
mixtures and solutions by their fixed
compositions. Have students recall
examples of mixtures and describe
how their compositions can vary.
Verbal
L1
Use Visuals
Figure 3 Have students examine the
wooden spheres shown in Figure 3.
Ask, Why do you think there are
holes in Dalton’s wooden spheres?
(One acceptable answer is that Dalton
used the holes in the spheres to connect
spheres together to construct models
of compounds.)
Visual, Logical
FYI
What did Dalton notice that all compounds have
in common?
Atomic Structure
101
Not every scientist was convinced that
Dalton had the physical evidence to
support the assumption that elements are
composed of indivisible particles called
atoms. William Whewell (1784–1868)
argued that particles could combine in
fixed proportions in compounds, but still
not be indivisible.
Customize for English Language Learners
Using Visual Aids
Have students draw simple illustrations for
the models of atoms according to Dalton,
Thompson, and Rutherford. Have them
describe each model to a partner using the
illustrations as a visual aid. Then, have each
pair of students discuss the similarities and
differences among the three models.
Answer to . . .
Figure 2 White
Dalton noticed that
the ratio of masses of
elements in a compound is always
the same.
Atomic Structure 101
Section 4.1 (continued)
Thomson’s Model
of the Atom
Sticky sides down
Investigating Charged Objects
Materials
4. Place the second piece, sticky side down,
directly over the first piece, as shown. Press
down firmly so the pieces stick together.
transparent tape, metric ruler, scissors
Procedure
Investigating
Charged Objects
L2
Objective
After completing this activity, students
will be able to
• explain that like charges repel and
unlike charges attract.
Skills Focus Observing, Drawing
Conclusions, Formulating
Hypotheses
Expected Outcome Students will
discover that the two pieces of tape are
attracted to one another after they are
pulled apart and then brought near one
another.
3. Place one piece of tape on a clean surface with
the sticky side facing down.
Analyze and Conclude
1. Drawing Conclusions What can you
conclude about the charges on the two
pieces of tape after they are separated?
2. Inferring What other objects have you
observed that became charged?
Thomson’s Model of the Atom
Figure 4 Amber is the hardened
form of a sticky, viscous liquid
that protects trees from insects
and disease. If amber is rubbed
with wool, it becomes charged
and can attract a feather.
Predicting What will happen
to the feather if the amber loses
its charge?
Analyze and Conclude
1. The two pieces of tape have opposite
charges because they attract when
brought close together.
2. Possible answers include clothes that
cling together when removed from a
dryer, and the charge that builds up
when a person walks across a carpet
(which is demonstrated by the spark
that occurs when the person touches
a doorknob).
Kinesthetic, Logical
When some materials are rubbed, they gain the ability to attract or
repel other materials. Glass and the amber in Figure 4 have this property. Based on their behavior, such materials are said to have either a
positive or a negative electric charge. Objects with like charges repel,
or push apart. Objects with opposite charges attract, or pull together.
Some charged particles can flow from one location to another. A flow
of charged particles is called an electric current. When you turn on an
appliance such as a hair dryer, a current flows from the wall socket
through the appliance. Joseph John Thomson (1856–1940), better known
as J. J. Thomson, used an electric current to learn more about atoms.
Thomson’s Experiments Thomson used a device like the one
shown in Figure 5A. At the center of the device is a sealed glass tube
from which most of the air has been removed. There is a metal disk at
each end of the tube. Wires connect the metal disks to a source of electric current. When the current is turned on, one disk becomes negatively
charged and the other disk becomes positively charged. A glowing
beam appears in the space between the disks.
Thomson hypothesized that the beam was a stream of charged particles that interacted with the air in the tube and caused the air to glow.
In one experiment Thomson did to test his hypothesis, he placed a pair
of charged metal plates on either side of the glass tube, as shown in
Figure 5B. The plates caused the beam to deflect, or bend, from its
straight path. Thomson observed that the beam was repelled by the
negatively charged plate and attracted by the positively charged plate.
FYI
If you do not want to present all the
experimental evidence for the atomic
theory, be sure students understand
attraction and repulsion of charged
particles and Rutherford’s nucleus model
of the atom.
6. Bring the separated strips close together
without touching. Record your observations.
2. Hold the pieces of tape by their folded ends
so that they are hanging straight down.
Then, without letting the pieces of tape touch,
slowly bring their sticky sides close together.
Record your observations.
Prep Time 5 minutes
Class Time 10 minutes
5. Remove the joined strips from the table.
Slowly peel the strips apart.
1. Cut two 10-cm pieces of tape. Fold over 1 cm
of tape at one end of each piece of tape to
form a “handle.”
102
Chapter 4
Facts and Figures
Charge People have known for thousands of
years that amber can attract other materials
after it has been rubbed with fur. Plato even
refers to these attractive powers of amber in
one of his dialogues.
102 Chapter 4
The labels positive and negative were
arbitrarily assigned by Benjamin Franklin
during his studies of electric charge and
electric current. (He also was the first to use
the terms battery and conductor.)
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Page 103
FYI
B
A
Sealed tube filled with
gas at low pressure
+
+
–
–
Negative
plate
Metal disk
Metal disk
Thomson used the speed of an electron,
its angle of deflection, and the strength
of the current to determine the chargeto-mass ratio of an electron. Robert
Milliken determined the actual mass
of an electron through his oil-drop
experiment.
Positive
plate
Glowing
beam
Source of
electric current
Metal disk
The current that flows through an
appliance is an alternating current. The
current Thomson used in his experiment
was a direct current. Not all movement
of charge is a current. Charge can flow
to or from a balloon (or between a hand
and a doorknob). With a current, charge
must flow continuously (at least until
the circuit is interrupted). The concepts
of electric charge and current are
addressed in depth in Chapter 20.
Source of
electric current
Figure 5 Thomson used a sealed tube of gas in his experiments.
A When the current was on, the disks became charged and a
glowing beam appeared in the tube. B The beam bent toward a
positively charged plate placed outside the tube.
Inferring What was the charge on the particles in the beam?
Evidence for Subatomic Particles Thomson concluded
that the particles in the beam had a negative charge because they were
attracted to the positive plate. He hypothesized that the particles came
from inside atoms. He had two pieces of evidence to support his
hypothesis. No matter what metal Thomson used for the disk, the par1
ticles produced were identical. The particles had about 2000
the mass
of a hydrogen atom, the lightest atom.
Thomson’s discovery changed how scientists thought about atoms.
Before his experiments, the accepted model of the atom was a solid ball
of matter that could not be divided into smaller parts.
Thomson’s
experiments provided the first evidence that atoms are made of even
smaller particles. Thomson revised Dalton’s model to account for these
subatomic particles.
Use Community
Resources
Figure 6 A scoop of chocolate
chip ice cream can represent
Thomson’s model of the atom.
The chips represent negatively
charged particles, which are
spread evenly through a mass of
positively charged matter—the
vanilla ice cream.
Have a physics or chemistry professor visit
the class and demonstrate Thomson’s
experiment using a cathode ray tube.
Encourage students to think of questions
to ask about how the experiment
demonstrates the properties of electrons.
Interpersonal, Visual
Build Reading
Literacy
Thomson’s Model An atom is neutral, meaning it has neither a
negative nor a positive charge. How can an atom contain negative particles and still be neutral? There must be some positive charge in the
atom. In Thomson’s model of the atom, the negative charges were
evenly scattered throughout an atom filled with a positively charged
mass of matter. The model is called the “plum pudding” model, after
a traditional English dessert.
You might prefer to think of Thomson’s model as the “chocolate
chip ice cream” model. Think of the chocolate chips in Figure 6 as the
negative particles and the vanilla ice cream as the positively charged
mass of matter. When the chocolate chips are spread evenly throughout the ice cream, their “negative charges” balance out the “positive
charge” of the vanilla ice cream.
L2
L1
Compare and Contrast Refer to
page 226D in Chapter 8, which
provides the guidelines for comparing
and contrasting.
Have students read about the different
atomic models described in Section 4.1.
Then, have students create a chart that
compares and contrasts each model.
Logical
How do objects with the same charge behave
when they come close to one another?
Atomic Structure
103
Answer to . . .
Figure 4 The feather will no longer
be attracted to the amber and will
drop to the ground.
Figure 5 Negative
Objects with the same
charge repel.
Atomic Structure 103
Section 4.1 (continued)
Rutherford’s Atomic Theory
Rutherford’s
Atomic Theory
FYI
Based on Figure 7, students might
conclude that Marsden used a circular
screen. The screen in the diagram
represents multiple positions of a smaller
screen that was moved from one position
to another while data was collected.
Alpha particles will be identified as
helium nuclei in Chapter 10.
Comparing Atomic
Models
When you try something new, you may have expectations about the
outcome. Does the outcome always meet your expectations or are you
sometimes surprised? Scientists can also be surprised by the results of
their experiments, but unexpected results can lead to important discoveries. This is what happened to Ernest Rutherford (1871–1937).
For: Links on atomic theory
Visit: www.SciLinks.org
Web Code: ccn-1041
Rutherford’s Hypothesis In 1899, Ernest Rutherford discovered that uranium emits fast-moving particles that have a positive
charge. He named them alpha particles. In 1909, Rutherford asked one
of his students, Ernest Marsden, to find out what happens to alpha
particles when they pass through a thin sheet of gold.
Recall that in Thomson’s model of the atom, the mass and positive
charge are evenly spread throughout an atom. Based on this model,
Rutherford hypothesized that the mass and charge at any location in
the gold would be too small to change the path of an alpha particle. He
predicted that most particles would travel in a straight path from their
source to a screen that lit up when struck. Those few that did not pass
straight through would be deflected only slightly.
L2
The Gold Foil Experiment Marsden used the equipment
Purpose Students will compare
different atomic models.
shown in Figure 7. He aimed a narrow beam of alpha particles at the
gold. The screen around the gold was made of a material that produced
a flash of light when struck by a fast-moving alpha particle. By observing the flash, Marsden could figure out the path of an alpha particle
after it passed through the gold.
Some of the locations of the flashes on the screen did not support
Rutherford’s prediction. More particles were deflected than he expected.
About one out of every 20,000 was deflected by more than 90 degrees.
Some of the alpha particles behaved as though they had struck an object
and bounced straight back.
Materials 3 clear, round bowls;
flavored gelatin mix; canned blueberries;
maraschino cherries
Procedure The day before, prepare the
flavored gelatin mix. Divide the liquid
gelatin evenly into the three bowls. Chill
slightly. Drain the blueberries and add
them to one of the bowls so that they
are distributed as evenly as possible in
the nearly gelled mix. Return the bowls
to the refrigerator. Right before class,
place a cherry in the center of the third
bowl. Have students discuss which
atomic models are represented by each
bowl of gelatin.
Figure 7 The path of an alpha
particle can be detected by the
location of a flash on a screen.
Rutherford expected the paths of
the positively charged alpha
particles that were aimed at the
thin gold foil to be affected only
slightly by the gold atoms. But
more particles were deflected
than expected and some particles
bounced straight back.
Deflected
particle
Undeflected
particle
90ⴗ
Expected Outcome The gelatin alone
represents Dalton’s atomic model. The
gelatin with blueberries represents
Thomson’s “plum-pudding” atomic
model, with the berries representing
electrons. The gelatin with the cherry
represents Rutherford’s atomic model.
Visual, Logical
Slit
Alpha
particles
Gold foil
Beam of
alpha
particles
Gold atoms
Actual results
Screen
Source of
alpha particles
104
Expected results
Alpha
particles
Nucleus
Chapter 4
Facts and Figures
Download a worksheet on atomic
theory for students to complete,
and find additional teacher support
from NSTA SciLinks.
104 Chapter 4
In His Own Words In a lecture Rutherford
gave at Cambridge in 1936, he recalled his
reaction when Geiger told him about alpha
particles being scattered backward by the
gold foil. Rutherford described his reaction.
“It was almost as incredible as if you fired a
15-inch shell at a piece of tissue paper and it
came back and hit you.”
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Page 105
Build Science Skills
Discovery of the Nucleus The alpha particles whose
paths were deflected must have come close to another charged
object. The closer they came, the greater the deflection was.
But many alpha particles passed through the gold without
being deflected. From these results, Rutherford concluded that the positive charge of an atom is not evenly
spread throughout the atom. It is concentrated in a
very small, central area that Rutherford called the
nucleus. The nucleus is a dense, positively charged
mass located in the center of the atom. (The plural of
nucleus is nuclei.)
Because Thomson’s model no longer explained
all the evidence, Rutherford proposed a new model.
According to Rutherford’s model, all of an atom’s
positive charge is concentrated in its nucleus. The alpha
particles whose paths were deflected by more than 90 degrees
came very close to a nucleus. The alpha particles whose paths were
not bent moved through the space surrounding the nuclei without
coming very close to any nucleus.
Figure 8 shows the inside of the Astrodome, a domed stadium in
Houston, Texas. The roof of the stadium rises to a height of 202 feet
above the center of the field. If an atom had the same volume as the stadium, its nucleus would have the volume of a marble. The total volume
of an atom is about a trillion (1012) times the volume of its nucleus.
Using Models Have students model the
gold foil experiment by shooting marbles
across the floor at an arrangement of
widely spaced, small objects—such as
beads that are glued to a flat surface—
and recording the angle of the marbles
that are deflected. Discuss the results of
their experiment in light of Marsden’s
findings.
Kinesthetic, Interpersonal
Integrate Biology
Figure 8 The Houston Astrodome
occupies more than nine acres and
seats 60,000 people. If the stadium
were a model for an atom, a
marble could represent its nucleus.
Using Analogies In the model,
where would the marble have to
be located in the stadium to
represent the nucleus?
1.
2.
3.
4.
5.
What theory did Dalton propose about
the structure of matter?
What evidence did J. J. Thomson provide
about the structure of an atom?
What did Rutherford discover about the
structure of an atom?
What evidence did Thomson have that his
glowing beam contained negative particles?
Why was Dalton’s model of the atom changed
after Thomson’s experiment?
Critical Thinking
6. Comparing and Contrasting Explain why
scientists accepted Dalton’s atomic theory but
not the idea of an atom proposed by the
Greek philosophers.
7. Drawing Conclusions If you observed
a beam of particles being bent toward a
negatively charged plate, what might
you conclude?
8. Relating Cause and Effect In the
Rutherford experiment, why weren’t all
the alpha particles deflected?
Section 4.1
Assessment
1. All matter is composed of individual
particles called atoms, which cannot be
divided.
2. Thomson provided the first evidence that
atoms are made from even smaller particles.
3. All of the positive charge of an atom is
concentrated in its nucleus.
4. The beam was attracted to a positively
charged plate and repelled by a negatively
charged plate.
Cells in most living organisms have a
central structure called a nucleus. This
organelle contains the cell’s genetic, or
hereditary, material. Ask, How are an
atom’s nucleus and a cell’s nucleus
similar? (They are both central structures
of a basic unit.)
Logical
3 ASSESS
Evaluate
Understanding
L2
L1
Reteach
Use the Science and History time line
on p. 114 to present and discuss a
summary of the three models.
Writing to Persuade Imagine you live in
ancient Greece. Assume all you know about
matter is what you can observe with your five
senses. You have heard the views of both
Democritus and Aristotle about matter. Write
a paragraph supporting one of their views.
Atomic Structure
L2
Ask groups of students to summarize
Dalton’s, Thompson’s, and Rutherford’s
atomic theories. Have them come up
with simple word phrases or mnemonic
devices to help them easily distinguish
among the three theories. For example,
Dogs Sort Socks Dalton’s Solid Sphere;
Turtles Play Ping-pong Thomson’s
Plum Pudding; and Rats Poke Noodles Rutherford’s Positive Nucleus.
Section 4.1 Assessment
Reviewing Concepts
L2
105
5. Dalton assumed atoms were solid,
indivisible particles. Thomson had evidence
that smaller particles existed inside atoms.
6. Dalton had data from experiments to
support his theory, whereas the Greeks did
not have data.
7. The particles have a positive charge.
8. The nucleus is small compared with the
atom as a whole. Very few of the alpha
particles came close enough to a gold nucleus
to be deflected.
Students might argue that the
properties Democritus assigned to
atoms match observed properties of
matter, such as smoothness and
roughness. Students might argue that
the properties Aristotle assigned to
elements serve a similar purpose, and
his system also seems to account for
changes between types of matter.
If your class subscribes to
the Interactive Textbook, use it to
review key concepts in Section 4.1.
Answer to . . .
Figure 8 The marble would have to
be located in the center of the stadium.
Atomic Structure 105
Small-Scale
Construction
Small-Scale Construction
L2
Background
Some scientists and engineers think of atoms and molecules as
construction materials for building very small objects.
The diameter of one of the silicon gears
is 50 microns (50,000 nanometers).
Despite their relative sizes on the
page, the silicon gear is much larger
than the model of nanogears. (The
atomic radius of a carbon atom is only
770 nanometers.)
In 1959, Richard Feynman suggested
the possibility of nanometer-scale
construction when he said, “The
principles of physics, as far as I can see,
do not speak against the possibility of
maneuvering things atom by atom.”
The uses for small-scale construction
are potentially very diverse, though
currently they are very limited. Biologists
already use nanotechnology to make
tiny labels for use in diagnostic and
pharmaceutical research. Such
molecular labels can be injected or
absorbed in one part of the body and
then traced as they travel throughout
the body. One company has even made
a sunscreen with nanometer-sized
particles that scatter harmful light rays
while transmitting visible light, which
makes the cream clear instead of white.
Build Science Skills
The field of science called nanotechnology is named for a unit
of measurement—the nanometer. A billion nanometers (109 nm)
can fit in one meter. The diameter of a human hair is about
80,000 nm. Scientists and engineers who use nanometers as
measuring units are building miniature versions of objects
such as motors.
There are two general methods for building any object.
You can start with more material than you need and
shape the object by removing matter or you can
build up the object from smaller pieces. When you
shape your nails with an emery board, you are using a
top-down construction method. When you see “some
assembly required” on the side of a box, the manufacturer
expects you to use a bottom-up method of construction.
Dust mite
L2
Silicon gear
Using Models
assembly
Purpose Students will
explore the difference
between top-down and
bottom-up methods of construction.
Building from the top down
Gears are toothed disks that are
designed to fit together so that the
motion of one gear controls the
motion of another. These silicon gears
are among the smallest objects ever
made from the top down.
Materials modeling clay, plastic knives
Class Time 10 minutes
Procedure Have students use the topdown method to construct a model of a
gear like the one shown in the dust mite
photo. Consider bringing in samples of
gears for students to observe. Then,
have students use the bottom-up
method to construct a model of the
stick figure shown in the feature.
Expected Outcome Students will
make a gear by starting with a lump of
clay and then removing clay to shape
the gear (a top-down construction
method). They will make a stick figure
by joining small pieces of clay together
(a bottom-up method of construction).
Kinesthetic, Visual
106 Chapter 4
106
Chapter 4
Building from the bottom up
With a scanning tunneling
microscope, it is possible to move
individual atoms or molecules.
This figure, made of linked carbon
monoxide molecules, is just five
nanometers (0.000005 mm) tall. In
1990, scientists built this figure to
demonstrate bottom-up
construction methods.
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Going Further
Possible uses include bar codes that
attach to molecules and are used
to monitor biological processes,
devices that deliver drugs to specific
locations in the body at specific times,
and self-assembling products. One
overall challenge is the construction
of interfaces between humans and
tiny devices.
Verbal, Visual
Futuristic model of a
nanorobot performing
surgery in a blood vessel.
The future of
nanotechnology
Potential applications for
nanotechnology include
medical diagnostic tools and
atomic-level electronic devices that
assemble themselves. If such devices
prove successful, perhaps someday
the surgical robot will be built.
Sheet of carbon atoms
rolled into a tube
Ring of carbon atoms with
hydrogen atoms attached
Going Further
Nanogears
This image of nanogears was produced
with a computer program designed to
make models of molecules. Hollow tubes
(nanotubes) made from sheets of carbon
atoms do exist. So do the rings containing
carbon and hydrogen atoms, which are used
for the “teeth” of the gears. But researchers
need to figure out how to get the “teeth”
to attach to the tubes.
Research proposed uses of nanotechnology.
Make a poster describing one proposed use.
Explain the advantage of
using small objects in this
application. What problems
must be solved before the
application can be used?
Take a Discovery Channel
Video Field Trip by watching
“Go For Gold.”
Video Field Trip
Atomic Structure
Video Field Trip
Go For Gold
After students have viewed the Video Field Trip,
ask them the following questions: What did the
ancient Egyptians know about how gold reacts
with air? (They realized that gold does not react
easily with air and does not corrode like many other
metals.) Name a practical reason why temple
roofs were often covered with gold in countries
with hot climates. (Because gold is an excellent
107
reflector of sunlight, it kept the interiors cooler than
they would have been otherwise.) How do the
properties of gold make it useful on space
missions? (Gold is often used to coat space vehicles
in order to reflect the intense sunlight. A thin layer of
gold on the goggles used by astronauts reduces the
intensity of light reaching the astronauts’ eyes.)
How can the arrangement of atoms on the
surface of gold be observed? (Electron
microscopes are designed to trace the arrangement
of particles on a surface through the up-and-down
movement of a probe tip.)
Atomic Structure 107
Section 4.2
4.2 The Structure of an Atom
1 FOCUS
Objectives
4.2.1
4.2.2
Identify three subatomic
particles and compare their
properties.
Distinguish the atomic number
of an element from the mass
number of an isotope, and use
these numbers to describe the
structure of atoms.
Key Concepts
Vocabulary
What are three subatomic
particles?
◆
What properties can be
used to compare protons,
electrons, and neutrons?
◆
How are atoms of one
element different from
atoms of other elements?
◆
◆
◆
◆
proton
electron
neutron
atomic number
mass number
isotopes
Reading Strategy
Monitoring Your Understanding Before
you read, copy the table. List what you know
about atoms and what you would like to learn.
After you read, list what you have learned.
What I Know
About Atoms
What I Would
Like to Learn
What I Have
Learned
What is the difference
between two isotopes of
the same element?
Reading Focus
Build Vocabulary
L2
Word-Part Analysis Have students
look up the term isotope in a dictionary
that provides word prefixes. Have them
use the prefix iso- to help them
understand the term. (The prefix isomeans “same.” Isotopes of an element
have the same atomic number, but
different numbers of neutrons.)
Reading Strategy
Figure 9 This 45-foot-tall steel
sculpture of a clothespin is in
Philadelphia, Pennsylvania. Claes
Oldenburg made the clothespin
in 1976 from 10 tons of steel. If a
proton had a mass of 10 tons,
then an electron would have a
mass of about 5 kilograms.
By 1920, Rutherford had seen evidence for the existence of two subatomic particles and had predicted the existence of a third particle.
Protons, electrons, and neutrons are subatomic particles.
Protons Based on experiments with elements other than gold,
Rutherford concluded that the amount of positive charge varies among
elements. Each nucleus must contain at least one particle with a positive charge. Rutherford called these particles protons. A proton is a
positively charged subatomic particle that is found in the nucleus of an
atom. Each proton is assigned a charge of 1⫹. Some nuclei contain
more than 100 protons.
2 INSTRUCT
Properties of
Subatomic Particles
Electrons The particles that Thomson detected were later named
electrons. Electron comes from a Greek word meaning “amber.” An
electron is a negatively charged subatomic particle that is found in the
space outside the nucleus. Each electron has a charge of 1⫺.
L1
Figure 9 Have students examine the
photo and the caption that describes
it in Figure 9. Suggest some familiar
objects that have a mass of 5 kg, such
as a 12-pack of 16-ounce beverage
containers. Ask, If a proton’s mass was
10 tons and an electron’s mass was
5 kg, what mass would represent the
mass of a neutron? (10 tons)
Logical
FYI
Different books use different conventions
for symbols for subatomic particles. For
example, some texts use only the letters
e, p, and n. Others include a superscript
zero on the n to indicate the lack of
charge. Electrons, protons, and neutrons
are not the only subatomic particles.
Quarks will be discussed in Chapter 10.
108 Chapter 4
eams like the ones Thomson produced create the images on many
television screens. When a beam sweeps across the screen, spots on the
screen light up in the same way the screen in the gold-foil experiment
lit up when struck by an alpha particle. In a color television, there are
three beams, one for each primary color of light—red, green, and blue.
The particles in these beams are subatomic particles.
Properties of Subatomic Particles
L2
Most students will know that atoms are
the “building blocks” of matter, and
some may know that atoms contain
subatomic particles. Students may say
that they want to learn more about the
structure of atoms.
Use Visuals
B
108
Chapter 4
Section Resources
Print
• Reading and Study Workbook With
Math Support, Section 4.2 and
Math Skill: Electrons and Orbitals
• Transparencies, Section 4.2
Technology
• Interactive Textbook, Section 4.2
• Presentation Pro CD-ROM, Section 4.2
• Go Online, Science News, Atomic chemistry
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Page 109
Properties of Subatomic Particles
Particle
Symbol
Relative
Charge
Relative Mass
(proton ⴝ 1)
Actual Mass
(g)
Electron
eⴚ
1ⴚ
1
1836
9.11 ⴛ 10ⴚ28
Proton
pⴙ
1ⴙ
1
1.674 ⴛ 10ⴚ24
Neutron
n
0
1
1.675 ⴛ 10ⴚ24
Model
Figure 10 This table lists the
symbol, the relative charge, the
relative mass, and the actual mass
of an electron, a proton, and a
neutron. The Model column
shows the colors used in this book
to represent the subatomic
particles. Calculating What is
the difference in actual mass
between a proton and a neutron?
Neutrons In 1932, the English physicist James Chadwick designed
an experiment to show that neutrons exist. Chadwick concluded that
the particles he produced were neutral because a charged object did
not deflect their paths. A neutron is a neutral subatomic particle that
is found in the nucleus of an atom. It has a mass almost exactly equal
to that of a proton.
Comparing Subatomic Particles
Figure 10 summarizes some properties of protons, electrons, and neutrons.
Protons, electrons, and neutrons can be distinguished by
mass, charge, and location in an atom. Protons and neutrons have
almost the same mass. But the data in Figure 10 show that it would
take about 2000 electrons to equal the mass of one proton. Electrons
have a charge that is equal in size to, but the opposite of, the charge of
a proton. Neutrons have no charge. Protons and neutrons are found in
the nucleus, but electrons are found in the space outside the nucleus.
Comparing Subatomic
Particles
Build Science Skills
Calculating Have students confirm
the relative masses given in Figure 10 by
dividing the mass given for an electron
by the mass given for a neutron.
(9.11 1028/1.675 1024 =
5.44 104; 1/1836 = 5.45 104)
These numbers are almost equal. Note
that the masses given are in grams.
Logical
Designing an
Atomic Exhibit
For: Articles on atomic chemistry
Visit: PHSchool.com
Web Code: cce-1042
L2
L2
Defining the Problem To design
an exhibit that compares the size of a
lithium atom to the size of its nucleus,
students must decide what materials to
use and where to locate the exhibit.
Organizing Information It is 60,000
times larger than its nucleus.
Creating a Solution If a standard
marble with a 5/8-inch diameter (1.6 cm)
represents the nucleus, the marker should
be at a distance of 960 m to represent
the outer limit of the atom.
Designing an Atomic Exhibit
You work as a volunteer at the local science
museum. You are asked to design an exhibit that
compares the size of a lithium atom to the size of
its nucleus. A lithium atom has a diameter of about
3 102 picometers. The nucleus_ of a lithium atom
has a diameter of about 5 10 3 picometers.
There are a trillion (1012) picometers in a meter.
Defining the Problem State the problem in
your own words. What decisions will you need
to make before you can proceed?
Organizing Information How many times
larger is the lithium atom than its nucleus? Find
several objects that could represent the nucleus
in your exhibit and measure their diameters.
Creating a Solution Pick one of the objects you
measured to represent the nucleus in your atomic
exhibit. Figure out how far away from the object
you would have to place a marker so that people
could visualize the relative sizes of the atom and
the nucleus.
Presenting Your Plan Write a proposal to
present to the committee that approves projects.
Tell them where you would place the nucleus and
where you would have to place the marker. Be
prepared to explain why your exhibit needs the
space you are requesting.
Atomic Structure
Presenting Your Plan The proposal
should explain why the exhibit requires
at least two locations that are about a
kilometer apart to make a model of the
lithium atom in which the nucleus is the
size of a marble. Encourage students to
locate two familiar area landmarks that
are the appropriate distance apart based
on the item chosen for the nucleus.
Visual, Logical
For Extra Help
109
L1
Be sure that students multiply by the
conversion factor that has the given unit
in the denominator and the desired unit
in the numerator.
Logical
Customize for Inclusion Students
Visually Impaired
Provide visually impaired students with a
tactile model that represents the difference
in mass between a proton and an electron.
Count out (or have a group of students count
out) 1836 small beads and place them into a
resealable plastic bag. Have them feel the
difference in mass between the bag of
1836 beads and an identical bag containing
only one bead. Point out that the masses
they sense include the masses of the bags.
Science News provides students
with current information on
atomic chemistry.
Answer to . . .
Figure 10 0.001 1024 g
Atomic Structure 109
Section 4.2 (continued)
Everything scientists know about the nucleus and subatomic particles is based on how the particles behave. Scientists still do not have
an instrument that can show the inside of an atom. But they do
have microscopes that can show how atoms are arranged on the surface of a material. The How It Works box on page 111 describes one of
those microscopes.
Atomic Number and
Mass Number
FYI
The atomic mass unit will be introduced
in Section 5.2, when atomic masses
listed in the periodic table are discussed.
The force that binds protons and
neutrons together in the nucleus is
called the strong nuclear force and is
addressed in Chapter 10, as is the effect
of the size of a nucleus on its stability.
Figure 11 Each element has a
different atomic number. A The
atomic number of sulfur (S) is 16.
B The atomic number of iron (Fe)
is 26. C The atomic number of
silver (Ag) is 47.
Applying Concepts How many
protons are there in each atom of
sulfur, iron, and silver?
L2
Purpose Students will observe the
relationship between number of
protons, number of neutrons, atomic
number, and mass number.
Materials overhead projector, red and
green gummy candies
Procedure Explain that the green
candies represent neutrons and the red
candies represent protons. Model a
lithium-7 nucleus by placing a group
of three red candies and four green
candies on the overhead. Ask students
to count the number of candies
(particles) to determine the mass
number of the lithium atom. Then,
remove (subtract) the green candies
(neutrons) to get the atomic number.
Perform a similar demonstration with
oxygen-16 (eight protons and eight
neutrons) and boron-11 (five protons
and six neutrons).
B
L1
Identify Main Idea/Details Refer
to page 98D in this chapter, which
provides the guidelines for identifying
main ideas and details.
Have students read Atomic Number and
Mass Number on p. 110. Ask them to
identify the main idea of each paragraph.
Point out that the main idea is usually
within the first or second sentence of a
paragraph. Encourage students to
include this exercise in the notes they
use to study.
Verbal
110 Chapter 4
Dalton predicted that the atoms of any element are different from the
atoms of all other elements. With the discovery of subatomic particles,
scientists were able to describe those differences.
Mass Number The atomic number tells you the number
of protons in an atom’s nucleus. It does not give you any information about the number of neutrons in an atom. For that
information, you need to know the atom’s mass number. The
mass number of an atom is the sum of the protons and neutrons in the nucleus of that atom. An atom of aluminum with
13 protons and 14 neutrons has a mass number of 27. If you
know the atomic number and the mass number of an atom,
you can find the number of neutrons by subtracting.
C
Expected Outcome Students should
gain a familiarity with determining mass
numbers and atomic numbers.
Visual
Build Reading Literacy
Atomic Number and Mass Number
Atomic Number The atoms of any given element always
have the same number of protons. For example, there is one
proton in the nucleus of each and every hydrogen atom.
Therefore, hydrogen is assigned the atomic number 1. The
atomic number of an element equals the number of protons
in an atom of that element.
Hydrogen atoms are the only atoms with a single proton.
Atoms of different elements have different numbers of
protons. The sulfur shown in Figure 11A is assigned atomic
number 16 because a sulfur atom has 16 protons. You can use
atomic numbers to refer to elements, like names and symbols,
because each element has a unique atomic number.
Each positive charge in an atom is balanced by a negative
charge because atoms are neutral. So the atomic number of an
element also equals the number of electrons in an atom. Each
hydrogen atom has one electron. Each sulfur atom has 16.
A
Particles and Numbers
Which scientist demonstrated the existence
of neutrons?
Number of Neutrons
Number of neutrons Mass number Atomic number
110
Chapter 4
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Page 111
Scanning Tunneling
Microscope
Scanning Tunneling
Microscope
A probe is moved back and forth across the surface of a
sample. When electrons jump, or tunnel, across the gap
between the sample and the probe, an electric current is
produced. A computer uses data about changes in the
probe’s position to produce an image of the sample’s
surface. Interpreting Diagrams How is the distance
between the probe tip and the sample kept constant?
Scanning probe
As the probe is moved
over the sample, current
flows between the probe
tip and the sample. The
processor holds the tip at a
constant distance from the
sample by keeping the
electric current constant.
Thus, changes in the vertical
position of the probe will
follow the contours of the
sample’s surface.
The scanning tunneling microscope
(STM) is used to obtain high-resolution
images of solid surfaces. This technology
allows scientists and researchers to view
a three-dimensional profile of a surface,
which can give information about
surface textures and crystal structure.
STM data is initially displayed as a black
and white image that is colorized to
highlight different features.
In 1986, Gerd Binnig of Germany and
Heinrich Rohrer of Switzerland shared the
Nobel Prize in Physics with Germany’s
Ernst Ruska for designing the scanning
tunneling microscope.
Scanning tunneling
microscope
Modern scanning tunneling
microscopes produce images of
metal samples or biological
specimens such as DNA.
Processor
The processor sends,
receives, and records
information about the
movement of the probe.
Electrical
signal from
processor
Interpreting Diagrams The processor
maintains a constant electric current
between the probe tip and the sample,
which keeps the distance between the
tip and sample constant.
Logical
Electrical
signal from
probe
For Enrichment
Gold
sample
L3
Encourage students to explore the use
of scanning tunneling microscopes in
research on surface textures, crystal
structure, or molecular shape. Have
them present their findings to the class
in the form of a poster.
Visual
Scanning
device This
device raises
and lowers
the probe.
Electron flow
Electrons flow across a gap
of about one nanometer
(0.000001 mm)
between the
probe tip and
the sample,
producing
an electric
current.
L2
Computer A computer
assembles a map of the
sample’s surface, using data
received from the processor.
Color was added to the
image shown on the
computer screen.
Probe tip The tip of
the probe is only one or
two atoms in width.
Atomic Structure
111
Facts and Figures
Coining Terms The English physician
William Gilbert (1544–1603) introduced the
term electric, which is based on the Greek
word for amber. (William Gilbert was the
personal physician to Queen Elizabeth I and
a pioneer in the study of magnetism. A unit of
magnetic force is named for him.) Credit for
naming the electron goes to G. Johnstone
Stoney, an Irish physicist who suggested the
name in 1891.
Answer to . . .
Figure 11 There are 16 protons in a
sulfur atom, 26 in an iron atom, and
47 in a silver atom.
James Chadwick
Atomic Structure 111
Section 4.2 (continued)
Comparing Ordinary Water
and Heavy Water
Isotopes
Build Science Skills
In Dalton’s atomic theory, all the atoms of a given element are
identical. Every atom of a given element does have the same
0.00ⴗC
Melting
3.81ⴗC
number of protons and electrons. But every atom of a given
point
element does not have the same number of neutrons. Isotopes
100.00ⴗC
Boiling
101.42ⴗC
are atoms of the same element that have different numbers of
point
neutrons and different mass numbers.
Isotopes of an ele0.99701 g/cm3
Density
1.1044 g/cm3
ment have the same atomic number but different mass
(at 25ⴗC)
numbers because they have different numbers of neutrons.
For example, every atom of oxygen has 8 protons. Some oxygen
Figure 12 Heavy water contains
hydrogen-2 atoms, which have
atoms have 8 neutrons and a mass number of 16. Some oxygen atoms
twice the mass of hydrogen-1
have 9 neutrons and a mass number of 17. Some oxygen atoms have
atoms. Using Tables At what
10 neutrons and a mass number of 18. When it is important to distintemperature would a sample of
heavy water freeze?
guish one oxygen isotope from another, the isotopes are referred to as
oxygen-16, oxygen-17, and oxygen-18. All three oxygen isotopes can
react with hydrogen to form water or combine with iron to form rust.
With most elements, it is hard to notice any differences in the physical or chemical properties of their isotopes. Hydrogen is an exception.
Hydrogen-1 has no neutrons. (Almost all hydrogen is hydrogen-1.)
Hydrogen-2 has one neutron, and hydrogen-3 has two neutrons.
Because a hydrogen-1 atom has only one proton, adding a neutron
doubles its mass. Water that contains hydrogen-2 atoms in place of
hydrogen-1 atoms is called heavy water. Figure 12 compares some
physical properties of ordinary water and heavy water.
Property
L2
Calculating Uranium-238 has a mass
number of 238 with 146 neutrons in the
nucleus. Uranium-235 has 143 neutrons
in the nucleus. Ask, What is the atomic
number of uranium? (92)
Logical
L2
Many students think that isotopes are
different from “ordinary” or “regular”
atoms. To challenge this misconception,
have students read the text on this page
and examine the data presented in
Figure 12. Ask, How are the compositions of heavy water and ordinary
water similar? (Both contain hydrogen
and oxygen atoms.) What type of
hydrogen atoms does ordinary water
contain? (Hydrogen-1 atoms) What type
of hydrogen atoms does heavy water
contain? (Hydrogen-2 atoms) Compare
the properties of heavy water and
ordinary water. (They have different
melting points, boiling points, and
densities.)
Logical
1.
2.
3.
L2
4.
5.
6.
L1
7.
Revisit Figure 10 to review the differences
among protons, neutrons, and electrons.
112
Students might say that “type of atom”
refers to the atomic number of the atom
or to the number of protons in the atom.
If your class subscribes to
the Interactive Textbook, use it to
review key concepts in Section 4.2.
Answer to . . .
Figure 12 3.81°C
112 Chapter 4
Heavy Water
Reviewing Concepts
Have students write three review
questions for this section. Students
should then break into groups of three or
four and ask each other their questions.
Reteach
Ordinary Water
Section 4.2 Assessment
3 ASSESS
Evaluate
Understanding
Isotopes
Name three subatomic particles.
Name three properties you could use to
distinguish a proton from an electron.
Which characteristic of an atom always
varies among atoms of different elements?
How are the isotopes of an element
different from one another?
What do neutrons and protons have in
common? How are they different?
How can atoms be neutral if they contain
charged particles?
What is the difference between atoms of
oxygen-16 and oxygen-17?
Critical Thinking
8. Comparing and Contrasting What
property do protons and electrons have
that neutrons do not?
9. Applying Concepts Explain why it isn’t
possible for an atom to have a mass number
of 10 and an atomic number of 12.
Elements In Section 2.1, you were told
that elements contain only one type of
atom. How would you define “type of
atom” to account for the existence
of isotopes?
Chapter 4
Section 4.2
Assessment
1. Proton, electron, and neutron
2. Mass, charge, and location in an atom
3. The atoms of any element have a different
number of protons than the atoms of all
other elements.
4. Isotopes of an element have the same
atomic number but different mass numbers
because they have different numbers
of neutrons.
5. Protons and neutrons have almost the same
mass and are both located in the nucleus of
the atom. Protons are charged particles.
Neutrons are neutral particles.
6. The positive charge of the protons in the
nucleus is balanced by the negative charge
of the electrons.
7. Each oxygen-17 atom has one more
neutron than each oxygen-16 atom.
8. Protons and electrons are charged particles.
Neutrons have no charge.
9. An atom with an atomic number of 12 has
12 protons. Because the mass number is the
sum of the protons and neutrons, the mass
number would need to be at least 12.
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Page 113
Section 4.3
4.3 Modern Atomic Theory
1 FOCUS
Objectives
Key Concepts
What can happen to
electrons when atoms
gain or lose energy?
What model do scientists
use to describe how
electrons behave in atoms?
Vocabulary
◆
◆
◆
◆
◆
energy levels
electron cloud
orbital
electron
configuration
ground state
Reading Strategy
4.3.1
Sequencing Copy the flowchart. After you
read, complete the description of how a gain
or loss of energy affects atoms.
4.3.2
Electrons and Energy Levels
a. ?
What is the most stable
configuration of electrons
in an atom?
Excited
state
b. ?
Emits
energy
4.3.3
Describe Bohr’s model of the
atom and the evidence for
energy levels.
Explain how the electron
cloud model represents the
behavior and locations of
electrons in atoms.
Distinguish the ground
state from excited states
of an atom based on
electron configurations.
H
ave you ever wondered what produces the different colors in
a fireworks display? Why does one explosion produce red light
and another explosion produce green light? The people who make
fireworks know that certain compounds will produce certain
colors of light when they are heated. For example, compounds
containing the element strontium produce red light when they
are heated. Compounds containing barium produce green light.
You have seen two things that can happen when atoms absorb
energy—an increase in kinetic energy or a phase change. But there
is another possibility. The energy may be temporarily absorbed by
the atom and then emitted as light. The colors in a fireworks display are a clue to how electrons are arranged in atoms.
Reading Focus
Build Vocabulary
LINCS Have students use the LINCS
strategy to learn the terms energy levels,
electron cloud, orbital, electron configuration, and ground state. In LINCS
exercises, students List what they know
about each term, Imagine a picture that
describes the term, Note a reminding
“sound-alike” word, Connect the terms
to the sound-alike word by making up
a short story, and then perform a brief
Self-test.
Bohr’s Model of the Atom
You may have seen diagrams of an atom that look like a solar
system with planets revolving around a sun. These diagrams are
based on a model of the atom that was developed by Niels Bohr
(1885–1962), a Danish physicist who worked for a while with
Rutherford. Bohr agreed with Rutherford’s model of a nucleus
surrounded by a large volume of space. But Bohr’s model did
something that Rutherford’s model did not do. It focused on the
electrons. A description of the arrangement of electrons in an
atom is the centerpiece of the modern atomic model.
Reading Strategy
L2
a. Electron moves to higher energy level.
b. Electron moves to lower energy level.
2 INSTRUCT
Bohr’s Model of
the Atom
Figure 13 Fireworks are often displayed above the
Lincoln Memorial in Washington, D.C. The red light
was produced by a strontium compound.
Build Reading Literacy
Atomic Structure
113
Section Resources
Print
• Laboratory Manual, Investigations 4A
and 4B
• Reading and Study Workbook With
Math Support, Section 4.3
• Transparencies, Section 4.3
L2
Technology
• Interactive Textbook, Section 4.3
• Presentation Pro CD-ROM, Section 4.3
• Go Online, NSTA SciLinks, Energy levels
L1
Relate Text and Visuals Refer to
page 190D in Chapter 7, which
provides the guidelines for relating
text and visuals.
Have students read Bohr’s Model of the
Atom on pp. 113–116. Then, have
students examine the diagram of Bohr’s
model in the time line on p. 115. Ask,
What do the circles around the nucleus
represent? (They represent energy levels.)
Visual
Atomic Structure 113
Section 4.3 (continued)
Energy Levels In Bohr’s model, electrons move with constant
speed in fixed orbits around the nucleus, like planets around a sun.
Each electron in an atom has a specific amount of energy. If an atom
gains or loses energy, the energy of an electron can change. The possible energies that electrons in an atom can have are called energy levels.
To understand energy levels, picture them as steps in a staircase.
As you move up or down the staircase, you can measure how your
position changes by counting the number of steps you take. You might
take one step up, or you might jump two steps down. Whether you are
going up or down, you can move only in whole-step increments. Just
as you cannot stand between steps on a staircase, an electron cannot
exist between energy levels.
L2
Students may think that electrons travel
around the nucleus in fixed orbits, like
planets orbiting the sun. Challenge this
misconception by having students
compare Bohr’s model and the electron
cloud model. Explain that Bohr’s model
correctly introduced the concept of
energy levels, but energy levels cannot
be used to describe the actual location
of an electron. The electron cloud model
can be used to model the probability
that an electron is in a certain location.
The exact speed and location of a single
electron cannot be determined.
Verbal
The positive charge of the
sphere balances the negative
charge of the electrons.
The development of scientific ideas on
the structure of atoms has passed several
key milestones during the last 200 years.
FYI
The usefulness of Bohr’s model was
limited. The model could be used to
describe the behavior of the single
electron in a hydrogen atom quite
accurately. However, this model
could not be applied to atoms with
multiple electrons.
Integrate Space Science
Models of the Atom
-
+
Planets in the solar system travel in
fixed orbits around the sun. Because
most of the orbits are nearly circular,
the difference between the distance to
the sun when a planet is closest and
when it is farthest away is not great
(given the magnitude of distances in
space). Pluto is an exception. Its orbit is
so elliptical that there are times during
Pluto’s journey around the sun (249
Earth days) when it is closer to the sun
than Neptune is. This switch in order
of proximity to the sun lasts 20 years.
It last happened between 1979 and
1999. Have students research when
it will happen again.
Logical
DALTON
MODEL
1803 John Dalton
pictures atoms as
tiny, indestructible
particles, with no
internal structure.
1800
114
Tiny,
solid
sphere
THOMSON
MODEL
1897 J. J. Thomson, a British
scientist, discovers the electron,
leading to his “plum-pudding”
model. He pictures electrons
embedded in a sphere of
positive electric charge.
1805
+
+
1895
-
+
-
+
+
+
-
L2
- -
Sphere with
positive charge
throughout
+
- +
Path of a
moving
electron
-
Nucleus
Negatively
charged particle
(electron)
1904 Hantaro
Nagaoka, a Japanese
physicist, suggests that
an atom has a central
nucleus. Electrons
move in orbits like the
rings around Saturn.
1900
-
RUTHERFORD
MODEL
1911 New Zealander
Ernest Rutherford
states that an atom has
a dense, positively
charged nucleus.
Electrons move
randomly in the space
around the nucleus.
1905
1910
Chapter 4
Customize for English Language Learners
Think-Pair-Share
Have students work in pairs to think of
structures that can serve as analogies for
energy levels. Examples include rungs of a
ladder, guitar frets, and the series of holes on a
belt or shoe strap. Note, however, that in all of
these models, the intervals are equal, which is
114 Chapter 4
not true of the intervals between energy levels.
Provide pictures of dressers that have drawers
of different sizes or bookshelves that have
adjustable shelves, which might better model
the intervals of energy levels. Strengthen
discussion skills by having students share
their examples with the class.
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The landing at the bottom of the staircase is like the lowest energy
level in an atom. Each step up represents a higher energy level. The
distance between two steps represents the difference in energy between
two energy levels. To continue the analogy, there would need to be a
different staircase for each element because no two elements have the
same set of energy levels.
An electron in an atom can move from one energy level to
another when the atom gains or loses energy. An electron may move
up two energy levels if it gains the right amount of energy. An electron in a higher energy level may move down two energy levels if it
loses the right amount of energy. The size of the jump between energy
levels determines the amount of energy gained or lost.
FYI
In Section 6.1, students will learn that
electrons sometimes gain enough
energy to escape from an atom.
Summary Select a scientist
mentioned on the time line.
Research and write a paragraph about the scientist’s
early years. What experiences
led to his interest in science?
Was he the first in his family
to be interested in science?
What subjects did he study
at school?
Electrons gain or
lose energy
when they move
between fixed
energy levels.
-
-
The nucleus
contains protons
and neutrons.
-
+
-
-
BOHR
MODEL
1913 In Niels
Bohr’s model, the
electrons move in
spherical orbits at
fixed distances
from the nucleus.
1915
The electron cloud is
a visual model of the
probable locations of
electrons in an atom.
The probability of
finding an electron is
higher in the denser
regions of the cloud.
Electron
Nucleus
ELECTRON
CLOUD
MODEL
1924 Frenchman Louis
de Broglie proposes that
moving particles like
electrons have some
properties of waves.
Within a few years,
evidence is collected to
support this idea.
1920
1926 Erwin Schrödinger
develops mathematical
equations to describe the
motion of electrons in
atoms. His work leads to
the electron cloud model.
1925
1930
1932 James
Chadwick, a British
physicist, confirms the
existence of neutrons,
which have no charge.
Atomic nuclei contain
neutrons and positively
charged protons.
115
L2
Have groups of students build or draw
models that represent the changes over
time in scientists’ understanding of
atomic structure. Have them make a
three-dimensional version of the time
line shown and display it as a mobile or
diorama. Have students note the time
scale on the time line. Explain that the
break between 1805 and 1895 allows
the milestone in 1803 to be included.
Group, Visual
There will be more information for some
scientists than for others. The exercise
focuses on early experiences because
students will not understand most of
what is written about the careers of
these scientists. By pooling their
research, students will see that scientists
can emerge from diverse backgrounds.
Students may learn that Dalton was
the son of a weaver and de Broglie
was the son of a duke; that Dalton
began his teaching career at the age
of 12; that Schrödinger was an only
child, but Rutherford had 11 siblings;
or that Chadwick was shy and
Rutherford charming.
Verbal
Use Community
Resources
1935
Atomic Structure
Models of
the Atom
L2
Have a female scientist visit the class to
discuss the experiences that led to her
interest in science. Have students
prepare questions similar to those asked
in the Writing in Science feature.
Interpersonal, Visual
Facts and Figures
De Broglie and Schrödinger In 1924,
Louis de Broglie, a French graduate student,
derived an equation that describes the
wavelength of a moving particle. Using
de Broglie’s equation, an electron has a
wavelength of about 2 1010 cm. In 1926,
Erwin Schrödinger, an Austrian physicist,
wrote a mathematical equation to describe
the location and energy of the electron in a
hydrogen atom. When the equation is solved
(using advanced calculus), it produces a series
of wave functions that describe the behavior
of electrons. The quantum mechanical model
of atoms is based on these wave functions.
Atomic physicists define an orbital as the
space-dependent part of the Schrödinger wave
function of an electron in an atom or molecule.
Atomic Structure 115
Section 4.3 (continued)
Evidence for Energy Levels What evidence is there that elec-
Electron Cloud
Model
Build Science Skills
L2
Using Models Have students examine
the propeller in Figure 14. Ask, How is
the moving propeller similar to an
electron cloud? (You cannot be sure at
any specific moment where the propeller
blades or electrons are located. However,
the central part of the propeller and the
nucleus of an atom are in fixed locations.)
What other examples can you think of
that could model the concept of an
electron cloud? (Acceptable answers
include a ceiling fan, or moths flying
around a light bulb.)
Visual
Electron Cloud Model
For: Links on energy levels
Visit: www.SciLinks.org
Web Code: ccn-1043
What determines the amount of energy gained or
lost when an electron moves between energy levels?
Electron Cloud Model
L2
Purpose Students will use a model
to describe the probable position of
electrons.
Materials small, round balloon;
large, round balloon; 10 beads with
4-mm diameter; 5 beads with
2-mm diameter
Procedure Put the 4-mm beads into
the small balloon. Tell students that the
small balloon represents the nucleus of a
boron atom (five neutrons, five protons).
Put the 2-mm beads into the large
balloon. Explain that the beads represent
electrons and the balloon represents the
electron cloud. Slightly inflate the small
balloon and push it completely into the
large balloon. Inflate the large balloon
and tie the end. Agitate the balloon so
that the small beads are in constant
motion.
Expected Outcome The precise
location of a bead at a specific time is
unknown, but the probability that it
is in the large balloon is quite high.
Kinesthetic
trons can move from one energy level to another? Scientists can
measure the energy gained when electrons absorb energy and move to
a higher energy level. They can measure the energy released when the
electron returns to a lower energy level.
The movement of electrons between energy levels explains the light
you see when fireworks explode. Light is a form of energy. Heat produced by the explosion causes some electrons to move to higher energy
levels. When those electrons move back to lower energy levels, they
emit energy. Some of that energy is released as visible light. Because
no two elements have the same set of energy levels, different elements
emit different colors of light.
Figure 14 When the propeller of
an airplane is at rest, you can see
the locations of the blades. When
the propeller is moving, you see
only a blur that is similar to a
drawing of an electron cloud.
Comparing and Contrasting
Describe one difference between
the motion of a propeller and the
motion of an electron.
116
Like earlier models, Bohr’s model was improved as scientists made
further discoveries. Bohr was correct in assigning energy levels to electrons. But he was incorrect in assuming that electrons moved like
planets in a solar system. Today, scientists know that electrons move in
a less predictable way.
Scientists must deal with probability when trying to predict the
locations and motions of electrons in atoms. An electron cloud is a
visual model of the most likely locations for electrons in an atom. The
cloud is denser at those locations where the probability of finding an
electron is high.
Scientists use the electron cloud model to
describe the possible locations of electrons around the nucleus.
Figure 14 provides an analogy for an electron cloud. When the propeller of an airplane is at rest, you can count the number of blades.
When the propeller is moving, the blades spin so fast that you see only
a blur. You know that the blades are located somewhere in the blur,
but at any specific moment in time you can’t be exactly sure where
each blade is located.
Chapter 4
Facts and Figures
Download a worksheet on energy
levels for students to complete,
and find additional teacher support
from NSTA SciLinks.
116 Chapter 4
Emission and Absorption Spectra When
the energy gained or lost by an atom is light
energy, each frequency (or wavelength) of
light corresponds to a movement of an
electron between two energy levels in the
atom. An element can be identified by the
frequencies of light that are absorbed or
emitted by its atoms because no two elements
have the same set of energy levels. For
example, the element helium was discovered
on the sun in 1868 before it was discovered on
Earth. The spectrum of light emitted by gases
on the surface of the sun contained a yellow
line that did not match a known element.
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Atomic Orbitals
Comparing Excited States
Materials
Comparing Excited
States
fluorescent (“neon”) markers, glow-in-the-dark
toy, ultraviolet (UV) lamp
Procedure
Analyze and Conclude
1. Use the fluorescent markers to draw a picture
on a piece of paper.
1. Observing How did the glow of the toy
differ from the glow of your drawing?
2. With the room darkened, observe your
drawing under a UV lamp. CAUTION Do not
look directly at the light. Remove the drawing
from under the UV light and observe it again.
Record your observations.
2. Formulating Hypotheses Use the concepts
of ground and excited states to explain how
UV light caused your drawing and the toy
to glow.
3. Observe the glow-in-the-dark toy under the
UV light. Remove the toy from the light and
observe it again. Record your observations.
3. Drawing Conclusions In which object, your
drawing or the toy, do the atoms have excited
states that are more stable, or less likely to
change? Explain your answer.
L2
Objective
After completing this activity, students
will be able to
• explain how UV light causes objects
to glow.
• use the persistence of light to
compare excited states.
Skills Focus Observing, Formulating
Hypotheses
Prep Time 5 minutes
Class Time 15 minutes
Atomic Orbitals
The electron cloud represents all the orbitals in an atom. An orbital is
a region of space around the nucleus where an electron is likely to be
found. To understand the concept of an orbital, imagine a map of your
school. Suppose you mark your exact location with a dot once every
10 minutes over a period of one week. The places you visit the most—
such as your classrooms, the cafeteria, and the area near your
locker—would have the highest concentration of dots. The places you
visit the least would have the lowest concentration of dots.
Figure 15 The table lists the
The dots on your map are a model of your “orbital.” They describe
number of orbitals in the first four
your most likely locations. There are some locations in your orbital
energy levels of an atom. It also
lists the maximum number of
that you may not visit every week—such as the principal’s office or the
electrons in each energy level.
auditorium. These locations may not be represented by a dot on your
Inferring How many electrons
map. Despite such omissions, the dots on your map are a good model
can be in each orbital?
of how you usually behave in your orbital.
An electron
cloud is a good approximation of how electrons behave in
Energy Levels, Orbitals,
their orbitals.
and Electrons
The level in which an electron has the least energy—the
Energy
Number of Maximum Number
Level
Orbitals
of Electrons
lowest energy level—has only one orbital. Higher energy
levels have more than one orbital. Figure 15 shows the
1
1
2
number of orbitals in the first four energy levels of an atom.
2
4
8
Notice that the maximum number of electrons in an energy
3
9
18
level is twice the number of orbitals. Each orbital can contain
two electrons at most.
4
16
32
Atomic Structure
FYI
According to the quantum mechanical model,
an orbital is the mathematical function that
describes the behavior of an electron in space.
117
Safety Check the MSDS for the
markers to make sure that they are low
in VOCs (volatile organic compounds).
Students should not look directly at UV
light, which is harmful to the eyes.
Demonstrate safe use of the UV lamps
before allowing students to use them.
Teaching Tips
• Do this lab only after you teach
ground state and excited states.
Expected Outcome Fluorescent ink
will emit brilliant visible light under UV
light. This fluorescence will instantly
cease when the UV light is removed.
Phosphorescent (glow-in-the-dark)
objects will continue to emit visible light
even after the UV light is removed.
Analyze and Conclude
1. The toy still glowed after the UV light
was removed. The drawing did not.
2. The drawing and the toy absorbed
energy from the UV light. When electrons
moved to higher energy levels, the atoms
were in an excited state. When electrons
returned to lower energy levels, energy
was released as visible light.
3. The fact that the toy’s glow persisted
suggests that the excited state of atoms
in the toy was more stable than the
excited state of atoms in the drawing.
Visual, Kinesthetic
Answer to . . .
Figure 14 The propeller blades have
a single, set path, and the blades stop
moving when the engine is shut off.
Figure 15 Two
The size of the jump
between energy levels
Atomic Structure 117
Section 4.3 (continued)
Figure 16 A gymnast on a
balance beam is like an atom in
an excited state—not very stable.
Electron
Configurations
Use Visuals
L1
Figure 16 Extend the analogy of the
gymnast on the balance beam by having
students consider a gymnast doing an
entire routine on equipment such as a
balance beam, a pommel horse, parallel
bars, or uneven bars. In the analogy,
when is the configuration of the
gymnast like an atom in an excited
state? (When the gymnast is in a
precarious position, such as when the
gymnast is not in direct contact with
the equipment) In the analogy, when
is the gymnast most like an atom
in its ground state? (The gymnast is
in her most stable position when she
is standing on the floor.)
Logical
3 ASSESS
Evaluate
Understanding
How are the seats in your classroom arranged? Are they lined up neatly
in rows, or are they grouped in clusters? A configuration is an arrangement of objects in a given space. Some configurations are more stable
than others, meaning that they are less likely to change. The position
of the gymnast on the balance beam in Figure 16 is not very stable
because the beam is only 10 centimeters wide.
An electron configuration is the arrangement of electrons in the
orbitals of an atom.
The most stable electron configuration is the
one in which the electrons are in orbitals with the lowest possible
energies. When all the electrons in an atom have the lowest possible
energies, the atom is said to be in its ground state.
For example, lithium is a silvery-white metal with an atomic
number of 3, which means that a lithium atom has three electrons. In
the ground state, two of the lithium electrons are in the orbital of the
first energy level. The third electron is in an orbital of the second
energy level.
If a lithium atom absorbs enough energy, one of its electrons can
move to an orbital with a higher energy. This configuration is referred
to as an excited state. An excited state is less stable than the ground
state. Eventually, the electron that was promoted to a higher energy
level loses energy, and the atom returns to the ground state. Helium,
neon, argon, krypton, and xenon atoms returning from excited states
to the ground state emit the light you see in “neon” lights.
L2
Have students draw and label a diagram
that represents Bohr’s model of an
atom. Then, have students explain how
the electron cloud model differs from
Bohr’s model.
Reteach
Electron Configurations
Section 4.3 Assessment
Reviewing Concepts
1.
2.
L1
Use the diagrams on p. 115 in the
Science and History feature to review
Bohr’s model, energy levels, and
electron clouds.
3.
4.
5.
7. Making Judgments Was Rutherford’s model
of an atom incorrect or incomplete? Explain
your answer.
8. Posing Questions Apply what you know
about charged particles to the modern model
of the atom. Is there anything about the
behavior of electrons in atoms that is
unexpected? Explain your answer.
When is an electron in an atom likely to
move from one energy level to another?
What model do scientists use to describe
how electrons move around the nucleus?
Describe the most stable configuration
of the electrons in an atom.
What did Bohr contribute to modern
atomic theory?
What does an electron cloud represent?
Critical Thinking
The shelves in a bookcase can represent
energy levels in an atom. If students
know about potential energy, they may
compare what happens to the energy of
a book as it is moved between shelves
to the difference in energy between
electrons in different energy levels.
If your class subscribes to
the Interactive Textbook, use it to
review key concepts in Section 4.3.
6. Comparing and Contrasting A boron
atom has two electrons in the first energy level
and three in the second energy level. Compare
the relative energies of the electrons in these
two energy levels.
118
Chapter 4
Section 4.3
Assessment
1. Electrons are likely to move from one
energy level to another when atoms gain or
lose energy.
2. The electron cloud model
3. The most stable configuration is the one in
which the electrons are in orbitals with the
lowest possible energy.
4. Bohr contributed the idea that electrons
have energy levels with specific amounts
of energy.
118 Chapter 4
Describing Energy Levels Use a bookcase as
an analogy for the energy levels in an atom.
Use the analogy to write a paragraph about
electrons and energy levels. (Hint: Reread the
staircase analogy on pages 114 and 115.)
5. An electron cloud represents the most
probable locations of an electron in an atom.
6. The electrons in the second energy level will
have more energy than the electrons in the
first energy level.
7. Rutherford’s description of an atom was
correct, but incomplete. It did not provide as
much information about the behavior of the
electrons as later models.
8. Students may ask why the negatively
charged electrons are not drawn into the
nucleus by the positively charged protons.
CHEMISTRY
Chapter 4
CHAPTER
Atomic Structure
ASSESS PRIOR
KNOWLEDGE
Use the Chapter Pretest below to assess
students’ prior knowledge. As needed,
review these Science Concepts and
Math Skills with students.
Review Science Concepts
Section 4.1 Encourage students to
recall that compounds have fixed
compositions. Remind students
that an atom is the smallest particle
of an element.
Section 4.2 Have students review the
terms mass, volume, and density and the
units used for each.
Section 4.3 Review two things that can
happen when matter absorbs energy.
Review Math Skills
Scientific Notation Students will
need to know how to use scientific
notation to understand values for certain
properties of subatomic particles.
How do science concepts apply to your
world? Here are some questions you’ll be
able to answer after you read this chapter.
■
What uses are there for objects that are not
visible to the unaided eye? (page 106)
■
Which subatomic particle produces the
images on many television screens and
computer monitors? (Section 4.2)
■
How does the type of hydrogen atom in
water affect the properties of water?
(Section 4.2)
■
How do fireworks produce the colors you see
when the fireworks explode? (Section 4.3)
Direct students to the Math Skills in the
Skills and Reference Handbook at the
end of the student text.
These images of carbon were magnified as 䉴
much as 20 million times. Color was added to
the images to highlight features.
98
Chapter 4
Chapter Pretest
1. True or False: Compounds have fixed
compositions. (True)
2. What is an atom? (An atom is the smallest
particle of an element.)
3. Which of the following units is a unit
of mass? (c)
a. mL
b. °C
c. g
d. cm
98 Chapter 4
4. Volume is (c)
a. the straight-line distance between
two points.
b. the quantity of matter in an object.
c. the amount of space taken up by
an object.
d. a representation of an object or event.
5. What is density? (Density is the ratio of the
mass of a substance to its volume.)
6. Which two of the following events can
take place when a liquid absorbs energy?
(a and d)
a. The average kinetic energy of the
particles in the liquid increases.
b. The temperature decreases.
c. The liquid freezes.
d. The liquid changes to a gas.
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CHEMISTRY
ENGAGE/EXPLORE
Chapter Preview
4.1
Studying Atoms
4.2
The Structure of an Atom
4.3
Modern Atomic Theory
Video Field Trip
Go For Gold
How Can You
Study Objects That
Are Not Visible?
L2
Purpose In this activity, students make
inferences based on their observations
and conclude that indirect evidence
must be used to study the structure of
objects that are too small to see.
Skills Focus Observing, Inferring
How Can You Study Objects That Are Not Visible?
Prep Time 5 minutes
Procedure
Think About It
1. Make and record observations about the
contents of two sealed bags. Use your senses
of touch, smell, and hearing to help you make
your observations.
1. Inferring What evidence did you use to
predict what objects were in the bags and
how many objects were in the bags?
2. Predicting Based on your observations,
make a prediction about what objects could be
in each bag. Decide whether there is a single
object or more than one object in each bag.
Materials 2 sealed, brown paper bags
Advance Prep Place a single type of
small object in each bag. Possible
objects that can be identified by
properties other than sight are lemon
slices (odor), pennies (shape), rubber
bands (elasticity), sandpaper squares
(texture), and bells (sound). Use a letter
code to identify the object in each bag.
Seal the bags before distributing them
to students.
2. Evaluating and Revising Record one of the
predictions listed that fits your observations as
well as or better than your own prediction.
3. Designing Experiments Propose an
experiment that would test the prediction.
3. Your teacher will list on the chalkboard all of
the predictions from the class.
Class Time 10 minutes
Teaching Tips
• Use more than two types of objects so
each group of students does not have
an identical set.
• To model the study of atoms, ask
students not to open the bags at the
end of the activity.
• Ask students how they could apply
what they have learned in this activity
to the study of atoms, which are too
small to see.
Expected Outcome Students should
recognize that detailed observations can
reveal information about objects and
events that cannot be observed directly.
Atomic Structure
Video Field Trip
Go For Gold
Encourage students to view the Video Field Trip
“Go For Gold.”
99
Think About It
1. Acceptable student answers may
include sound, texture, hardness, smell,
and how objects move inside the bags.
2. Students may choose a prediction
that they did not record in Step 2 if this
prediction is a better fit for the evidence
they list for Question 1.
3. Answers should include a practical test
that would clearly support or contradict
the prediction chosen in Question 2.
Logical
Atomic Structure 99
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Using Flame Tests
Using Flame Tests
Objective
After completing this activity, students
will be able to
• observe that different substances
produce different colors when placed
in a flame.
Forensic scientists use various approaches to
distinguish different substances. In this lab, you
will observe the flame colors of several substances
and use the data to determine the identity of an
unknown substance.
Problem
How can the color of a flame be
used to distinguish substances?
Materials
• solutions of
calcium chloride,
boric acid,
potassium chloride,
copper(II) sulfate,
sodium chloride,
and an unknown
• Bunsen burner
• nichrome wire loop
• dilute solution of
hydrochloric acid
• wash bottle with
distilled water
Skills
5. Repeat Steps 3 and 4 with each of the other
solutions. Be careful not to transfer any
solution from one container to another.
CAUTION These chemicals are poisonous.
Do not let them get on your skin.
6. Obtain the unknown solution from your teacher.
Procedure
Part A: Observing Flame Colors
1. Make a copy of the data table shown.
7. Repeat Steps 3 and 4 using the unknown
solution. Compare your observations with
the other data you recorded to identify the
unknown. CAUTION Wash your hands
thoroughly before leaving the laboratory.
Flame
Color
Calcium chloride
Potassium chloride
Boric acid
Copper(II) sulfate
Sodium chloride
Unknown
Identity of Unknown
3. Dip the wire loop into the calcium chloride
solution and then place the loop in the flame
as shown. Observe and record the color of
the flame.
1. Comparing and Contrasting Is there a
relationship between the color of the flame
and the color of the solution?
2. Formulating Hypotheses How do these
substances produce light of different colors?
3. Drawing Conclusions A forensic scientist
does a flame test on a substance that was
found at a crime scene. What might the
scientist conclude if the flame turns green?
There is another test that you
can use to distinguish elements
by color. With your teacher supervising, dip a wire
loop in borax. Heat the loop in a flame until the
borax melts. Remove the loop from the flame and
let the borax cool. It will form a clear glass bead.
Dip the bead in a tiny sample of solid copper
sulfate and return the loop to the flame for a few
seconds. Remove the loop and observe the color
of the bead as it cools.
Atomic Structure
Prep Time 20 minutes
Advance Prep Provide each lab group
with a sample of each solution and
unknown in a small, labeled container
with a lid. Film canisters work well and
they can be obtained free of charge
from any photo shop. Prepare solutions
that are about 0.1 M. Provide 0.1 M HCl
in a glass container.
Safety Students need to wear safety
goggles and lab aprons. Review
proper use of the Bunsen burner and
appropriate safety precautions for using
flames. Make sure long hair is tied back
and loose clothing is not worn. Some of
the substances are extremely toxic if
ingested. Make sure students wash their
hands thoroughly before leaving the
laboratory.
Go Further
2. Light the Bunsen burner. CAUTION Put
on safety goggles and a lab apron. Tie back
loose hair and clothing before working with
a flame.
Skills Focus Observing, Predicting,
Using Data Tables, Drawing
Conclusions
Class Time 40 minutes
Analyze and Conclude
Data Table
Solution
4. Clean the loop by dipping it into hydrochloric
acid. Then, while holding the loop over a sink,
rinse away the acid with distilled water.
CAUTION Keep hydrochloric acid away from your
skin and clothing. Do not breathe in its vapor.
Part B: Examining an Unknown Solution
Observing, Predicting,
Using Data Tables
L2
119
Analyze and Conclude
1. There is no relationship between flame color
and solution color.
2. When the compounds are placed in the flame,
atoms absorb energy and electrons move to
higher energy levels. As these electrons move
back to lower energy levels, they release energy
as visible light. The color of light produced
depends on the difference in energy between
two specific energy levels in an atom.
3. The green flame indicates that the substance
may contain copper, barium, or boron.
Visual, Logical
Teaching Tips
• Demonstrate proper technique for
performing flame tests and cleaning
the wire loop between samples. Stress
the importance of not contaminating
one sample with another.
• Have students test the sodium
chloride solution last because it can
remain on the loop and make it
difficult to see the other colors.
• Stress the importance of recording
specific colors, for example, “fireengine red” instead of simply “red.”
Expected Outcome Students should
be able to make accurate observations
of flame colors and use them to identify
their unknown solutions.
Sample Data
The following flame colors are
characteristic: calcium: orange;
potassium: violet; boron: light-green;
copper: green; sodium: yellow-orange.
Go Further
The copper-glass bead will change from
green to blue as it cools.
Kinesthetic, Visual
Atomic Structure 119
Planning Guide
SECTION OBJECTIVES
STANDARDS
NATIONAL
4.1
Studying Atoms, pp. 100–105
1 block or 2 periods
4.1.1
4.1.2
4.1.3
4.2
A-1, A-2, B-1,
B-2, B-6, E-2,
G-1, G-2, G-3
ACTIVITIES and LABS
STATE
SE Inquiry Activity: How Can You
Study Objects That Are Not
Visible? p. 99
L2
SE Quick Lab: Investigating Charged
Objects, p. 102
L2
TE Teacher Demo: Comparing Atomic
Models, p. 104
L2
A-1, B-1, B-2,
E-1, G-1, G-2,
G-3
TE Teacher Demo: Particles and
Numbers, p. 110
L2
A-1, A-2, B-1,
B-2, G-1, G-2,
G-3
SE Quick Lab: Comparing Excited
States, p. 117
L2
Describe ancient Greek models
of matter.
List the main points of Dalton’s atomic
theory and describe his evidence for the
existence of atoms.
Explain how Thomson and Rutherford
used data from experiments to produce
their atomic models.
The Structure of an Atom, pp. 108–112
1 block or 2 periods
4.2.1
Identify three subatomic particles and
compare their properties.
4.2.2
Distinguish the atomic number of an
element from the mass number of an
isotope, and use these numbers to
describe the structure of atoms.
4.3
Easy Planner
Teacher Express
Modern Atomic Theory, pp. 113–118
1 block or 2 periods
4.3.1
Describe Bohr’s model of the atom and
the evidence for energy levels.
SE Forensics Lab: Using Flame
Tests, p. 119
L2
4.3.2
Explain how the electron cloud model
represents the behavior and locations of
electrons in atoms.
TE Teacher Demo: Electron Cloud
Model, p. 116
L2
Distinguish the ground state from
excited states of an atom based on
electron configurations.
LM Investigation 4A: Constructing
a Model of an Atom
L2
LM Investigation 4B: Modeling
an Electron Cloud
L1
4.3.3
98A Chapter 4
Ability Levels
Components
L1 For students who need additional help SE
TE
L2 For all students
LM
L3 For students who need to be challenged PLM
Student Edition
Teacher’s Edition
Laboratory Manual
Probeware Lab
Manual
RESOURCES
SECTION
PRINT and TECHNOLOGY
ASSESSMENT
RSW
Section 4.1
L1
DC Go For Gold
L2
RSW
Reading & Study
Workbook
MSPS Math Skills &
Problem Solving
Workbook
CUT
CTB
TP
DC
Chapter & Unit Tests
Computer Test Bank
Test Prep Resources
Discovery Channel
Videotapes & DVDs
Section 4.1
P Chapter 4 Pretest
Section 4.1
GO Atomic theory
SE Section 4.1
Assessment, p. 105
Web Code: cca-1040
Web Code: ccn-1041
Web Code: ccn-1043
L2
Web Code: cce-1042
L2
L2
L2
Materials for Activities and Labs
L2
Quantities for each group
TEACHER’S EDITION
STUDENT EDITION
Teacher Demo, p. 104
3 clear, round bowls; flavored
gelatin mix; canned blueberries;
maraschino cherries
Inquiry Activity, p. 99
2 sealed, brown paper bags
RSW
Section 4.2
RSW Math Skill
L1
L2
SE Section 4.2
Assessment, p. 112
iT Section 4.2
T Section 4.2
L2
P Section 4.2
L2
RSW
Section 4.3
L2
L1
T Section 4.3
L2
P Section 4.3
L2
Quick Lab, p. 102
transparent tape, metric
ruler, scissors
Quick Lab, p. 117
fluorescent (“neon”) markers,
glow-in-the-dark toy, ultraviolet
(UV) lamp
Forensics Lab, p. 119
solutions of calcium chloride,
boric acid, potassium chloride,
copper(II) sulfate, sodium
chloride, and an unknown;
Bunsen burner; nichrome wire
loop; dilute solution of
hydrochloric acid; wash bottle
with distilled water
GO Atomic
chemistry
Transparencies
Interactive Textbook
Presentation Pro
CD-ROM
GO Internet Resources
Go online for these Internet resources.
iT Section 4.1
T Chapter 4 Pretest
T
iT
P
SE Section 4.3
Assessment, p. 118
Build Science Skills, p. 106
modeling clay, plastic knives
Teacher Demo, p. 110
overhead projector, red and
green gummy candies
Teacher Demo, p. 116
small, round balloon; large,
round balloon; 10 beads with
4-mm diameter; 5 beads with
2-mm diameter
Chapter Assessment
iT Section 4.3
GO Energy levels
L2
CHAPTER ASSESSMENT
STANDARDIZED TEST PREP
SE
SE
TP
Chapter Assessment,
pp. 121–122
CUT Chapter 4 Test A, B
CTB Chapter 4
iT
Chapter 4
PHSchool.com GO
Web Code: cca-1040
Chapter 4, p. 123
Diagnose and Prescribe
Interactive Textbook with
assessment at PHSchool.com
Atomic Structure 98B
Before you teach
From the Author
David Frank
Ferris State University
Big Ideas
Once students have some understanding of the properties
that are used to describe and classify matter, they need
theories to explain why matter behaves in predictable
ways. In Chapter 3, students used kinetic theory to explain
the behavior of solids, liquids, and gases. The atomic
theory presented in Chapter 4 will be used in Chapters 6
and 7 to explain bonding and chemical reactions.
Matter and Change In the nineteenth and early
twentieth centuries, scientists refined models of the
atom based on strong indirect evidence. Section 4.1
describes some of the methods scientists used to gather
evidence about atomic structure. You can use Section 4.1
to help students understand the relationship between
scientific laws (which summarize observed patterns in
nature) and theories (which explain these observed
patterns). Dalton’s atomic theory is a case in point. In his
theory, Dalton described properties of atoms that could
explain the law of conservation of mass and the law of
definite proportions.
Some people think that a theory must be discarded if
evidence is discovered that contradicts the theory. More
often, a theory is revised to account for new evidence.
For example, the discovery of isotopes disproved
Dalton’s assumption that every atom of an element had
the same mass. Subsequently, the atomic theory was
revised to state that every atom of an element has the
same number of protons, but not necessarily the same
number of neutrons.
Forces and Motion The idea that oppositely
charged particles attract and that similarly charged
particles repel is a fundamental concept in science. The
attraction of particles to a positive plate in Thomson’s
experiment demonstrated the negative charge of these
particles (electrons). The repulsion of positively charged
alpha particles in the gold foil experiment demonstrated
that the nucleus of an atom has a positive charge.
98C Chapter 4
Chemistry Refresher
Ancient Models of Atoms
4.1
Democritus of Abdera thought that the shapes and sizes of the
atoms in a material determined the properties of the material.
Atoms were seen as constantly moving in space, sometimes colliding and forming groups. Later, Aristotle gained authority for
his idea that all substances were built up from only four elements
because his proposals fit with the existing worldview throughout
the Middle Ages. Much of alchemy was based on the theory that
elements could be transformed into other elements through the
qualities they possessed in common.
Evidence for Dalton’s Theory
4.1
In 1802, John Dalton proposed the law of partial pressures of
gases: A gas in a mixture of gases contributes the same pressure
it would produce if it were the only gas in a container. In 1803,
Dalton proposed the law of definite proportions, which states
that elements form compounds in certain fixed ratios. Dalton’s
work with gas pressure and with the composition of compounds
led him to consider the fundamental nature of matter. He presented his atomic theory in a series of lectures in 1807.
Dalton’s Symbols for Some Elements
Symbol
Chemical Name
Symbol
Chemical Name
Hydrogen
Carbon
Azote (Nitrogen)
Oxygen
Subatomic Particles
J.J. Thomson studied the flow
of current through gases in a
sealed tube. He used a magnet
to deflect the cathode rays. He
could not use an electric field
because the passage of the rays
through the tube caused the
gas to become a conductor.
The conducting gas screened
the particles in the rays from
the effect of the external electric field. When Thomson
removed almost all the gas
from the tube, the effect of the
field could be seen.
4.1 and 4.2
Many students think that
isotopes are different from
“ordinary” or “regular”
atoms. However, isotopes
are atoms of an element
that have differing nuclear
compositions. For a
strategy to overcome this
misconception, see
Address Misconceptions
on page 112.
For: Teaching methods for atomic structure
Visit: www.SciLinks.org/PDLinks
Web Code: ccn-0499
In 1909, Ernest Rutherford (who had worked with Thomson)
asked Ernest Marsden (an undergraduate student from New
Zealand) to find out whether any alpha particles were scattered by
more than a few degrees as they passed through foil. Marsden used
a sheet of gold foil that was only 0.00004 (4 ⫻ 10⫺5) cm thick.
After World War I, Rutherford experimented with bombarding
nitrogen atoms with alpha particles. Some of the nitrogen atoms
released hydrogen nuclei and transmuted into oxygen atoms. He
concluded that these nuclei were released from the nitrogen nuclei
and that they were fundamental particles. He is usually credited
with naming these particles protons, after the Greek word protos,
meaning “first.” Although Rutherford predicted the existence of
neutrons in 1920, it was his research assistant, James Chadwick,
who provided the supporting evidence.
Electrons and Energy Levels
Students may think that
electrons travel around
the nucleus in fixed orbits,
like planets orbiting
the sun. However, the
exact path or location
of an electron cannot
be determined. For a
strategy to overcome
this misconception, see
Address Misconceptions
on page 114.
4.3
In a staircase, the distance
between steps is (ideally) constant from step to step. In an
atom, the difference in energy
between energy levels is not
constant. It decreases as the
quantum number of the energy
level (n) increases. The specific
amount of energy that is
absorbed or released when an
electron moves between energy
levels is called a quantum of
energy. When the energy
absorbed or released by an atom
is light energy, the quanta are
called photons.
Build Reading Literacy
Identify Main Idea/Details
Locating Topic Sentences in Paragraphs
Strategy Help students understand and remember the most
important information about a topic. This strategy can be
applied to short segments of text, such as a single paragraph or
a subsection, to find the main idea and details that support the
topic. Assign students a short passage to read, such as The Gold
Foil Experiment on p. 104.
Example
1. Tell students that many paragraphs have a topic sentence that
expresses the paragraph’s main idea. Topic sentences are often
the first or second sentence in the paragraph. Sometimes,
however, they are the last sentence, or even a sentence in the
middle of the paragraph.
2. Then, explain that the rest of the paragraph contains details,
or additional facts and examples about the main idea.
3. Direct students’ attention to a paragraph with a clearly stated
topic sentence, and ask students which sentence best states the
main idea of the paragraph.
4. Next, help students find sentences with details that explain
more about the main idea.
5. Have students organize the main idea and details visually in a
web format.
6. Have students work in pairs to identify the main idea and
details in another passage and organize them in a web.
See p. 110 for a script on how to use the identify main
ideas/details strategy with students. For additional Build
Reading Literacy strategies, see pp. 103 and 113.
Photon Emission as a Result
of Energy Level Transitions
ΔE 4
ΔE 3
ΔE 2
n=4
n=3
n=2
Energy level
Increasing energy
n=5
n=1
Decreasing photon wavelength
Atomic Structure 98D
Chapter 4
CHAPTER
4
Study Guide
Study Guide
4.1
Study Tip
Organize New Information
Tell students to organize the key
information from the chapter into one
comprehensive document. They should
consider creating an outline, a chart, a
set of flashcards, a time line, or a concept
map to help them visualize the relationships. For example, they might wish to
organize all of the information in this
chapter on an annotated time line. They
could include drawings that illustrate
each atomic model. They could also label
the drawings with vocabulary terms and
their definitions.
Thinking Visually
a. p
b. 1
c. 0
d. 1
e. 1
Studying Atoms
Key Concepts
• Dalton proposed the theory that all matter is made
up of individual particles called atoms, which
cannot be divided.
• Thomson’s experiments provided the first evidence
that atoms are made of even smaller particles.
• According to Rutherford’s model, all of an atom’s
positive charge is concentrated in its nucleus.
Vocabulary
nucleus, p. 105
4.2
The Structure of an Atom
Key Concepts
• Protons, electrons. and neutrons are
subatomic particles.
• Protons, electrons, and neutrons can be
distinguished by mass, charge, and location
in an atom.
• Atoms of different elements have different
numbers of protons.
• Isotopes of an element have the same atomic
number but different mass numbers because
they have different numbers of neutrons.
Vocabulary
proton, p. 108
electron, p. 108
neutron, p. 109
atomic number, p. 110
mass number, p. 110
isotopes, p. 112
120
4.3
Modern Atomic Theory
Key Concepts
• An electron in an atom can move from one
energy level to another when the atom gains
or loses energy.
• Scientists use the electron cloud model to
describe the possible locations of electrons
around the nucleus.
• An electron cloud is a good approximation of how
electrons behave in their orbitals.
• The most stable electron configuration is the one
in which the electrons are in orbitals with the
lowest possible energies.
Vocabulary
energy levels, p. 114
electron cloud, p. 116
orbital, p. 117
electron configuration, p. 118
ground state, p. 118
Thinking Visually
Table of Properties Use information from the
chapter to complete the table below.
Particle
Proton
Symbol
a.
Relative charge
Relative mass
1ⴙ
d.
Electron
?
b.
?
1
1836
Chapter 4
Chapter Resources
Print
• Chapter and Unit Tests, Chapter 4
Test A and Test B
• Test Prep Resources, Chapter 4
120 Chapter 4
Neutron
eⴚ
?
Technology
• Computer Test Bank, Chapter Test 4
• Interactive Textbook, Chapter 4
• Go Online, PHSchool.com, Chapter 4
n
c.
?
e.
?
0098_hsps09te_Ch04.qxp
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Page 121
Assessment
CHAPTER
4
Assessment
Reviewing Content
Interactive Textbook with
assessment at PHSchool.com
Understanding Concepts
Choose the letter that best answers the question or
completes the statement.
11. Why must indirect evidence be used to study the
structure of atoms?
1. One of the first people to state that matter is
made up of atoms was
a. Democritus.
b. Aristotle.
c. Dalton.
d. Rutherford.
12. What evidence convinced Dalton that elements
must be made of individual particles called atoms?
2. Dalton’s model of an atom is best described as
a. a solar system.
b. a solid sphere.
c. a plum pudding. d. an electron cloud.
3. Who provided the first evidence that atoms
contain subatomic particles?
a. Dalton
b. Rutherford
c. Thomson
d. Bohr
4. Almost all the mass of an atom is located in its
a. protons.
b. electrons.
c. electron cloud.
d. nucleus.
13. In Thomson’s experiment, why was the glowing
beam repelled by a negatively charged plate?
14. What evidence supported Thomson’s hypothesis
that the negative particles he observed came
from inside atoms?
15. Compare the mass and volume of the nucleus to
the total mass and volume of an atom.
16. Compare the relative masses of protons,
neutrons, and electrons in an atom.
17. What is the difference between the atomic
number of an atom and its mass number?
5. An electron is a particle with
a. a negative charge, found in the nucleus.
b. a positive charge, found in the nucleus.
c. no charge, found outside the nucleus.
d. a negative charge, found outside
the nucleus.
18. If the atomic number of an atom is 11, how
many electrons does the atom have? Explain.
6. Which particle is the least massive?
a. proton
b. electron
c. neutron
d. nucleus
20. What part of Dalton’s theory was modified after
the discovery of isotopes?
7. All atoms of an element have the same
a. mass number.
b. number of isotopes.
c. atomic number. d. number of neutrons.
8. The number of neutrons in an atom equals the
a. mass number minus atomic number.
b. atomic number plus number of electrons.
c. mass number plus atomic number.
d. atomic number minus mass number.
9. The atomic number of sulfur is 16. How many
electrons are there in an atom of sulfur-34?
a. 16
b. 34
c. 18
d. 50
10. Atoms emit energy as light when
a. electrons move to a higher energy level.
b. electrons move to a lower energy level.
c. protons move to a higher energy level.
d. protons move to a lower energy level.
19. If an atom has an atomic number of 6 and a
mass number of 14, how many protons,
electrons, and neutrons are in the atom?
21. Which isotope of oxygen is represented by the
drawing—oxygen-16, oxygen-17, or oxygen-18?
Assume that all the protons and neutrons in the
nucleus are visible in the drawing. Give a reason
for your answer.
Electron cloud
Nucleus
Proton
Neutron
22. What is the main difference between Bohr’s
model of the atom and the atomic theory that is
currently accepted?
23. What does it mean to say that an atom is in an
excited state?
Atomic Structure
Homework Guide
Section
4.1
4.2
4.3
121
If your class subscribes
to the Interactive Textbook, your
students can go online to access an
interactive version of the Student
Edition and a self-test.
Reviewing Content
1.
4.
7.
10.
a
d
c
b
2. b
5. d
8. a
3. c
6. b
9. a
Understanding Concepts
11. Atoms are too small to observe
directly.
12. The ratio of the mass of elements in
a compound is always the same.
13. The beam contained negatively
charged particles, and like charges repel.
14. The particles were much less massive
than the lightest known atom. The same
particles were produced no matter
which metal was used as the origin of
the particles.
15. Almost all of the mass of an atom is
located in the nucleus. The volume of
the nucleus is much smaller than the
volume of the atom as a whole.
16. Protons and neutrons have almost the
same mass, which is about 2000 times
greater than the mass of an electron.
17. The atomic number represents the
number of protons or electrons in the
atom. The mass number represents the
number of protons and neutrons.
18. Because an atom must be neutral, it
has 11 electrons to balance the charge
on the 11 protons.
19. Six protons, six electrons,
eight neutrons
20. All atoms of an element are identical.
21. Oxygen-17 because there are
eight protons and nine neutrons
22. Bohr assumed that electrons
traveled in orbits around the nucleus.
Current atomic theory assumes that
electrons do not travel in fixed paths.
23. One or more of the electrons in an
atom have moved from the ground
state to an orbital with a higher energy.
Questions
1–2, 11–14, 24–25, 34
3–9, 15–21, 26–33, 37
10, 22–23, 35–36
Atomic Structure 121
PPLS
Chapter 4
CHAPTER
4
Critical Thinking
24. There are no external charged plates
in setup A.
25. Because neutrons have no charge,
the charged plates would not deflect
the beam.
26. Carbon-14
27. A neutral particle is more difficult to
detect than a charged particle because
charged plates do not deflect its path.
28. The atom would have a negative
charge, and atoms are neutral.
29. They are atoms of different elements
because they have different numbers of
protons. All atoms of a given element
have the same number of protons.
Assessment (continued)
Critical Thinking
Concepts in Action
24. Controlling Variables Look at the drawing of
the experimental setup in Figure 5A. Explain how
the setup is a control for the setup in Figure 5B.
25. Predicting How would the results of Thomson’s
experiment change if the beam were a stream of
neutrons instead of a stream of electrons?
26. Interpreting Diagrams The atomic number of
carbon is 6. The atomic number of nitrogen is 7.
The atomic number of oxygen is 8. Name the
isotope represented by the drawing.
Electron cloud
Nucleus
Concepts in Action
33. Iron-59 is different from other
isotopes of iron because it contains
33 neutrons. It is the same as other
isotopes because they all contain
26 protons.
34. Possible choices for the top-down
analogy include a stone sculpture, a clay
pot, or a carved wooden object, such as
a totem pole. Choices for the bottom-up
analogy include a brick wall, a bead
necklace, a tile floor, or a patchwork quilt.
35. You cannot be certain because
elements other than barium also may
produce a green color.
36. Each element used in neon lights
produces a distinctive color when
its atoms are excited. If there are
multiple colors, there must be multiple
elements present.
37. With a scanning tunneling
microscope, scientists can gather
previously unavailable data about atoms,
such as how atoms are arranged on
the surface of materials. An electron
microscope could not be developed until
scientists knew that electrons existed.
Proton
Neutron
27. Hypothesizing Why were the proton and
electron discovered before the neutron?
28. Applying Concepts Explain why a neutral
atom cannot have one proton, one neutron,
and two electrons.
29. Classifying The nucleus of an atom contains six
neutrons and six protons. The nucleus of a second
atom contains six neutrons and five protons. Are
they atoms of different elements or isotopes of the
same element? Explain your answer.
Math Skills
30. Calculating The atomic number for iron is 26.
How many neutrons are in the nucleus of an iron
atom with a mass number of 57? How many
electrons does the iron atom have?
32. Applying Concepts A helium-4 atom has twice
as many protons as a hydrogen atom. How many
protons and how many neutrons are in the
nucleus of a helium-4 atom?
122
Chapter 4
Students should ask at least one question about
the overall structure of an atom, the properties of
subatomic particles, and the behavior of
electrons. Students should be able to explain the
order they have chosen.
122 Chapter 4
36. Relating Cause and Effect Brightly colored
neon lights consist of tubes filled with a gas.
When an electric current passes through the
tubes, different colors are emitted. Why might
you conclude that the tubes in a multicolored
display contain more than one element?
37. Writing in Science Better technology leads to
an increase in scientific knowledge. An increase in
knowledge allows for the invention of new
technology. Write a paragraph discussing these
statements. Use a scanning tunneling microscope
as your example.
Performance-Based Assessment
Preparing a Survey Write ten questions you could
ask to find out what people know about the modern
model of an atom. Figure out the best order for the
questions to test someone’s knowledge fairly. Be
prepared to explain your choices.
31. Applying Concepts If a potassium atom has
an atomic number of 19 and a mass number of
39, how many protons, electrons, and neutrons
are in the atom?
Performance-Based Assessment
Your students can independently
test their knowledge of the chapter
and print out their test results for
your files.
34. Using Analogies Scientists working in the field
of nanotechnology use either a top-down or
bottom-up approach to construct tiny objects.
Give an example of a visible structure that was
made using the bottom-up approach and one
that was made using the top-down approach.
35. Inferring If you see a green color when
fireworks explode, can you be certain that the
fireworks contained a barium compound? Give
a reason for your answer.
Math Skills
30. 31 neutrons; 26 electrons
31. 19 protons, 19 electrons, 20 neutrons
32. Two protons and two neutrons
33. Comparing and Contrasting The compound
in blood that carries oxygen to cells throughout
the body contains iron. Iron has an atomic number
of 26. Iron-59 is used to diagnose disorders in the
blood. How is iron-59 different from all other
isotopes of iron? How is it the same?
For: Self-grading assessment
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Standardized Test Prep
Standardized Test Prep
Test-Taking Tip
Using Data Tables
When presented with a question that is related
to a data table, read the title of the table to see
what type of data it contains. Then look at the
headings of the columns and rows to see how
the data are organized. The table below lists
properties for subatomic particles. There is a row
for each particle and a column for each property.
Read the question to find out which data you
will need to answer the question. In this case,
you will need the data on relative charge.
Properties of Subatomic Particles
Particle
Symbol
Relative
Charge
Relative Mass
(proton = 1)
Electron
eⴚ
1ⴚ
1
_____
1836
Proton
pⴙ
1ⴙ
1
Neutron
n
0
1
1. A
4. E
2. C
5. D
3. B
6. C
2. According to Dalton’s atomic theory, an atom is
(A) made of smaller particles.
(B) a particle with a positive charge.
(C) the smallest particle of an element.
(D) in constant motion.
(E) a particle with a negative charge.
3. Electrons in the first energy level of an atom
(A) have no energy.
(B) have the lowest possible energy.
(C) have the highest possible energy.
(D) are in an excited state.
(E) are in an unstable state.
4. Most alpha particles pass through a thin layer of
gold without deflection because gold atoms
(A) are filled with positively charged matter.
(B) have no overall charge.
(C) have a negatively charged nucleus.
(D) do not have a nucleus.
(E) have a dense nucleus surrounded by space.
Use the data table to answer Question 5.
Comparison of Oxygen Isotopes
Which of the following statements is true?
(A) The charge on a proton is larger than the
charge on an electron.
(B) The charge on a proton is smaller than the
charge on an electron.
(C) The charge on a proton is identical to the
charge on an electron
(D) The charge on a proton is equal in size but
opposite to the charge on an electron.
(E) A proton is a neutral particle.
(Answer: D)
Choose the letter that best answers the question or
completes the statement.
1. J. J. Thomson demonstrated that electrons
(A) have a negative electric charge.
(B) have a positive electric charge.
(C) are repelled by a positively charged object.
(D) are attracted to a negatively charged object.
(E) do not have an electric charge.
Property
Oxygen-16
Oxygen-18
Protons
8
8
Neutrons
8
10
Electrons
8
8
Percentage
in nature
99.757
0.205
5. What is the mass number of oxygen-18?
(A) 8
(B) 10
(C) 16
(D) 18
(E) 0.205
6. An electron configuration describes
(A) regions of space around the nucleus of
an atom.
(B) possible energies that an electron can have.
(C) the arrangement of electrons in an atom.
(D) the emission of light from an excited atom.
(E) the number of possible orbitals in an atom.
Atomic Structure
123
Atomic Structure 123