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CHEMISTRY
Matter and Change
Chapter 4: The Structure of the Atom
CHAPTER
4
Table Of Contents
Intro-CFQ and Seeds Activity
Section 4.1
Early Ideas About Matter
Section 4.2
Defining the Atom
Section 4.3
How Atoms Differ
Section 4.4
Unstable Nuclei and Radioactive
Decay
Click a hyperlink to view the corresponding slides.
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SECTION
4.1
Early Ideas About Matter
• Compare and contrast the atomic models of Democritus,
Aristotle, and Dalton.
• Understand how Dalton's theory explains the conservation
of mass.
theory: an explanation supported by many experiments; is
still subject to new experimental data, can be modified, and
is considered successful if it can be used to make
predictions that are true
SECTION
4.1
Early Ideas About Matter
Dalton's atomic theory
The ancient Greeks tried to explain matter,
but the scientific study of the atom began
with John Dalton in the early 1800's.
Standards and CFQ
• Standards- highlight in your packet.
• Sc1a
• Sc3 a, c, d
• CFQ- Is nuclear power right for Social
Circle?
Pre – thoughts?
•
•
•
•
•
•
Write on a piece of paper
What do you know about nuclear power?
How could you find information about it?
What do expect to learn about it?
How could you apply what you learn?
CFQ Handout
What effect radiation have?
• Seeds lab
SECTION
4.1
Early Ideas About Matter
Greek Philosophers
• Many ancient scholars believed matter was
composed of such things as earth, water, air, and
fire.
• Many believed matter could be endlessly divided
into smaller and smaller pieces.
SECTION
4.1
Early Ideas About Matter
Greek Philosophers (cont.)
• Democritus (460–370 B.C.) was the first person to
propose the idea that matter was not infinitely divisible,
but made up of individual particles called atomos, from
which the English word atom is derived.
• Aristotle (484–322 B.C.) disagreed with Democritus
because he did not believe empty space could exist.
• Aristotle’s views went unchallenged for 2,000 years until
science developed methods to test the validity of his
ideas.
SECTION
4.1
Early Ideas About Matter
Greek Philosophers (cont.)
SECTION
4.1
Early Ideas About Matter
Greek Philosophers (cont.)
• John Dalton revived the idea of the atom in
the early 1800s based on numerous
chemical reactions.
• Dalton’s atomic theory easily explained
conservation of mass in a reaction as the
result of the combination, separation, or
rearrangement of atoms.
SECTION
4.1
Early Ideas About Matter
Greek Philosophers (cont.)
SECTION
4.1
Section Check
Who was the first person to propose
the idea that matter was not infinitely
divisible?
A. Aristotle
B. Plato
C. Dalton
D. Democritus
SECTION
4.1
Section Check
Dalton’s theory also conveniently
explained what?
A. the electron
B. the nucleus
C. law of conservation of mass
D. law of Democritus
SECTION
4.2
Defining the Atom
• Define atom.
• Distinguish between the subatomic particles in
terms of relative charge and mass.
• Describe the structure of the atom, including the
locations of the subatomic particles.
model: a visual, verbal, and/or mathematical
explanation of data collected from many
experiments
Vocab
• Use the words on the next slide to draw a
model of what you think an atom looks
like.
• What word is not a part of an atom?
SECTION
4.2
Defining the Atom
Atom
cathode ray
electron
nucleus
proton
neutron
An atom is made of a nucleus containing
protons and neutrons; electrons move
around the nucleus.
SECTION
4.2
Defining the Atom
The Atom
• The smallest particle of an element that
retains the properties of the element is
called an atom.
• An instrument called the scanning tunneling
microscope (STM) allows individual atoms to
be seen.
SECTION
4.2
Defining the Atom
The Electron
• When an electric charge is applied, a ray of
radiation travels from the cathode to the
anode, called a cathode ray.
• Cathode rays are a stream of particles
carrying a negative charge.
• The particles carrying a negative charge are
known as electrons.
SECTION
4.2
Defining the Atom
The Electron (Cont.)
• This figure shows a typical cathode ray
tube.
SECTION
4.2
Defining the Atom
The Electron (Cont.)
• J.J. Thomson measured the effects of both
magnetic and electric fields on the cathode ray to
determine the charge-to-mass ratio of a charged
particle, then compared it to known values.
• The mass of the charged particle was much less than
a hydrogen atom, then the lightest known atom.
• Thomson received the Nobel Prize in 1906 for
identifying the first subatomic particle—the electron
SECTION
4.2
Defining the Atom
The Electron (Cont.)
• In the early 1910s, Robert Millikan used the
oil-drop apparatus shown below to
determine the charge of an electron.
SECTION
4.2
Defining the Atom
The Electron (Cont.)
• Charges change in discrete amounts—
1.602  10–19 coulombs, the charge of one
electron (now equated to a single unit, 1–).
• With the electron’s charge and charge-tomass ratio known, Millikan calculated the
mass of a single electron.
the mass of
a hydrogen
atom
SECTION
4.2
Defining the Atom
The Electron (Cont.)
• Matter is neutral. You know that matter is neutral
from everyday experiences. You do not receive
an electric shock (except under certain
conditions) when you touch an object.
• If electrons are negative, then how is matter,
which is made up of electrons, neutral?
• J.J. Thomson proposed a model of the atom to
answer this question.
SECTION
4.2
Defining the Atom
The Electron (Cont.)
• J.J. Thomson's plum pudding model of the atom
states that the atom is a uniform, positively
charged sphere containing electrons.
The Shape of Things
• How can the shape of an object be
determined without actually seeing it with
your eyes?
• Shape of things activity
SECTION
4.2
Defining the Atom
The Nucleus
• In 1911, Ernest Rutherford studied how
positively charged alpha particles
interacted with solid matter.
• By aiming the particles at
a thin sheet of gold foil,
Rutherford expected the
paths of the alpha
particles to be only
slightly altered by a
collision with an electron.
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• Although most of the alpha particles went
through the gold foil, a few of them
bounced back, some at large angles.
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• Rutherford concluded that atoms are
mostly empty space.
• Almost all of the atom's positive charge and
almost all of its mass is contained in a dense
region in the center of the atom called the
nucleus.
• Electrons are held within the atom by their
attraction to the positively charged nucleus.
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• The repulsive force between the positively
charged nucleus and positive alpha
particles caused the deflections.
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• Rutherford refined the model to include
positively charged particles in the nucleus
called protons.
• James Chadwick received the Nobel Prize in
1935 for discovering the existence of
neutrons, neutral particles in the nucleus
which accounts for the remainder of an
atom’s mass.
History of the atom
• Timeline worksheet!
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• All atoms are made of three
fundamental subatomic
particles: the electron, the
proton, and the neutron.
• Atoms are spherically shaped.
• Atoms are mostly empty space,
and electrons travel around the
nucleus held by an attraction to
the positively charged nucleus.
Summarize!
• Summarize the last slide in your own
words. Does it match your original
thoughts of what you thought it looked
like?
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• Scientists have determined that protons
and neutrons are composed of subatomic
particles called quarks.
SECTION
4.2
Defining the Atom
The Nucleus (cont.)
• Scientists do not yet understand if or how
quarks affect chemical behavior.
• Chemical behavior can be explained by
considering only an atom's electrons.
SECTION
4.2
Section Check
Atoms are mostly ____.
A. positive
B. negative
C. solid spheres
D. empty space
SECTION
4.2
Section Check
What are the two fundamental subatomic
particles found in the nucleus?
A. proton and electron
B. proton and neutron
C. neutron and electron
D. neutron and positron
Practice Worksheet!
• Fill in what you know!
SECTION
4.3
How Atoms Differ
• Explain the role of atomic number in determining the
identity of an atom.
• Define an isotope.
• Explain why atomic masses are not whole numbers.
• Calculate the number of electrons, protons, and
neutrons in an atom given its mass number and
atomic number.
Fill in the following chart
• Use the diagram for each vocab word in
the next section
Your
def
Relate
to
atom
word
Book
def
picture
SECTION
How Atoms Differ
4.3
periodic table: a chart that organizes all known
elements into a grid of horizontal rows (periods)
and vertical columns (groups or families) arranged
by increasing atomic number
atomic number
atomic mass unit (amu)
isotopes
atomic mass
mass number
The number of protons and the mass
number define the type of atom.
SECTION
4.3
How Atoms Differ
Atomic Number
• Each element contains a unique positive
charge in their nucleus.
• The number of protons in the nucleus of an
atom identifies the element and is known as
the element’s atomic number.
SECTION
4.3
How Atoms Differ
Isotopes and Mass Number
• All atoms of a particular element have the
same number of protons and electrons but
the number of neutrons in the nucleus can
differ.
• Atoms with the same number of protons but
different numbers of neutrons are called
isotopes.
• Notation: Name- mass or _______ top
number is ______ ______ bottom is
__________ ___________ which is _______
Practice Problems
• Use the worksheet to practice your
notation!!!
SECTION
4.3
How Atoms Differ
Isotopes and Mass Number (Cont.)
• In nature, most elements are found as mixtures of
isotopes. Usually, the relative abundance of each
isotope is constant.
–Ex. In a banana, 93.26% is potassium-39,
6.73% is potassium-41 and 0.01% is potassium40. In another banana or in a different source of
potassium, the percentage composition of the
potassium isotopes will still be the same.
• Isotopes containing more neutrons have a greater mass.
• Isotopes of an atom have the same chemical behavior.
SECTION
4.3
How Atoms Differ
Isotopes and Mass Number (Cont.)
• The mass number is the sum of the protons
and neutrons in the nucleus.
More on that practice sheet
• What else can you fill in?????
SECTION
4.3
How Atoms Differ
Mass of Atoms
• One atomic mass unit (amu) is defined as
1/12th the mass of a carbon-12 atom.
• One amu is nearly, but not exactly, equal to
one proton and one neutron.
SECTION
4.3
How Atoms Differ
Mass of Atoms (cont.)
• The atomic mass of an element is the
weighted average mass of the isotopes of
that element.
What’s in the Bag?
• Isotope in a bag activity
SECTION
4.3
Section Check
An unknown element has 19 protons, 19
electrons, and 3 isotopes with 20, 21 and
22 neutrons. What is the element’s
atomic number? How do you know?
A. 38
B. 40
C. 19
D. unable to determine
SECTION
4.3
Section Check
Elements with the same number of
protons and differing numbers of
neutrons are known as what?
A. isotopes
B. radioactive
C. abundant
D. ions
SECTION
4.4
Unstable Nuclei and Radioactive Decay
• Explain the relationship between unstable nuclei and
radioactive decay.
• Characterize alpha, beta, and gamma radiation in
terms of mass and charge.
element: a pure substance that cannot be broken
down into simpler substances by physical or chemical
means
Kahoot!
• Find the definition of the following words
and get ready to Kahoot it up!
SECTION
4.4
Unstable Nuclei and Radioactive Decay
radioactivity
alpha particle
half life
radiation
nuclear equation
nuclear reaction
beta radiation
radioactive decay
beta particle
fusion
alpha radiation
gamma rays
fission
Unstable atoms emit radiation to gain
stability.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactivity
• Nuclear reactions can change one element into
another element.
• In the late 1890s, scientists noticed some
substances spontaneously emitted radiation,
a process they called radioactivity.
• The rays and particles emitted are called
radiation.
• A reaction that involves a change in an atom's
nucleus is called a nuclear reaction.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay
• Unstable nuclei lose energy by emitting
radiation in a spontaneous process called
radioactive decay.
• Unstable radioactive elements undergo
radioactive decay thus forming stable
nonradioactive elements.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
• Alpha radiation is made up of positively
charged particles called alpha particles.
• Each alpha particle contains two protons and
two neutrons and has a 2+ charge.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
• The figure shown below is a nuclear
equation showing the radioactive decay of
radium-226 to radon-222.
• Questions on notes.
2 a helium-4
• An alpha particle is equivalent to
nucleus and is represented by 4He or
.Thus, showing mass is conserved in a
nuclear equation.
Summary
• Summary of Alpha
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
• Beta radiation is radiation that has a
negative charge and emits beta particles.
• Each beta particle is an electron with a 1–
charge.
• During Beta decay, a neutron is converted to
a proton and an electron. The electron is
emitted and the proton stays in the nucleus.
Summary
• Where does this equation show the
conversion of a neutron into an electron
and proton?
• Prove it with numbers.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay – Explain this
picture!!!
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
• Gamma rays are high-energy radiation with no
mass and are neutral.
• They usually accompany alpha and beta
radiation.
• Gamma rays account for most of the energy lost
during radioactive decay.
Summary
• Explain all of the symbols and numbers for
the gamma equation.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay (cont.)
• Because gamma rays are massless, the emission
of gamma rays by themselves cannot result in the
formation of a new atom.
Did you know???
• Alpha particles are slow moving and big
and can be stopped by a piece of paper.
Alpha particles are used in smoke
detectors, treatment of tumors and a static
remover in paper mills.
• Beta particles are fast moving and can be
stopped by foil. They are used for
treatment of eye and bone cancer, tracers,
and used to test thickness of materials.
Did you Know????
• Gamma radiation is fast and strong. It can
be stopped by lead or concrete.
• Gamma rays are used to replace x-rays in
radiotherapy. They “zap” cancer cells.
They are also used to sterilize medical
instruments and prolong the life of foods
keeping them safe in packages longer.
Decay practice
• Practice worksheet on decay
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Radioactive Decay – WHY????/
• Atoms that contain too many or two few
neutrons are unstable and lose energy
through radioactive decay to form a stable
nucleus.
• Few exist in nature—most have already
decayed to stable forms.
Half Life
• Radioactive decay happens in certain
periods of time called half life.
• Half life is like shopping!
• Graph activity and twizzler lab.
Accelerated Chem
• www.Coolmath.com/algebra/17exponentials-logarithms/13-radioactivedecay-decibel-levels-01
Fusion
• Fusion is responsible for all elements
heavier than Hydrogen- Why?
• What is Hydrogen’s atomic number?
• What does this mean?
• How are elements heavier than that built?
• How?
Because….
• Fusion is the combination of nuclei in a
HIGH energy nuclear reaction.
• Fusion produces HUGE amounts of
energy
• Fusion happens on the sun
Draw it
What do you think?
What it really looks like
Fission
• Why would this word fit a nuclear bomb or
nuclear power plant?
Because…..
• Fission is a splitting of an atoms nucleus
• Fission releases large amounts of energy
but not as much as fusion
• Fission is used for bombs and nuclear
powerplants because it is controllable,
releases large amounts of energy and
doesn’t create air pollution in powerplants
CFQ Info
• Watch the two quick videos about nuclear
power. Rotate to the stations in the room
to fill out the chart about alternative fuel
sources. Fill out the chart to use some of
this info for your CFQ.
Info gathering
Main idea
Info to use to defend
and how will it be
used?
Cite source
SECTION
4.4
Section Check
A reaction that changes one element into
another in the nucleus of an atom is
called what?
A. chemical reaction
B. beta radiation
C. nuclear reaction
D. physical reaction
SECTION
4.4
Section Check
Why are radioactive elements rare in
nature?
A. They do no occur on Earth.
B. Most have already decayed to a
stable form.
C. They take a long time to form.
D. They are too hard to detect.
CHAPTER
The Structure of the Atom
4
Resources
Chemistry Online
Study Guide
Chapter Assessment
Standardized Test Practice
SECTION
Early Ideas About Matter
4.1
Study Guide
Key Concepts
• Democritus was the first person to propose the
existence of atoms.
• According to Democritus, atoms are solid,
homogeneous, and indivisible.
• Aristotle did not believe in the existence of atoms.
• John Dalton’s atomic theory is based on numerous
scientific experiments.
SECTION
Defining the Atom
4.2
Study Guide
Key Concepts
• An atom is the smallest particle of an element that
maintains the properties of that element.
• Electrons have a 1– charge, protons have a 1+ charge,
and neutrons have no charge.
• An atom consists mostly of empty space surrounding
the nucleus.
SECTION
How Atoms Differ
4.3
Study Guide
Key Concepts
• The atomic number of an atom is given by its
number of protons. The mass number of an atom is
the sum of its neutrons and protons.
atomic number = number of protons = number of electrons
mass number = atomic number + number of neutrons
• Atoms of the same element with different numbers of
neutrons are called isotopes.
• The atomic mass of an element is a weighted average of
the masses of all of its naturally occurring isotopes.
SECTION
4.4
Unstable Nuclei and Radioactive Decay
Study Guide
Key Concepts
• Chemical reactions involve changes in the electrons
surrounding the nucleus of an atom. Nuclear
reactions involve changes in the nucleus of an atom.
• There are three types of radiation: alpha (charge of 2+),
beta (charge of 1–), and gamma (no charge).
• The neutron-to-proton ratio of an atom’s nucleus
determines its stability.
CHAPTER
4
The Structure of the Atom
Chapter Assessment
Whose work led to the modern atomic theory?
A. Dalton
B. Rutherford
C. Einstein
D. Aristotle
CHAPTER
4
The Structure of the Atom
Chapter Assessment
Which particle is not found in the nucleus of an
atom?
A. neutron
B. proton
C. gamma ray
D. electron
CHAPTER
4
The Structure of the Atom
Chapter Assessment
Two isotopes of an unknown element have the
same number of:
A. protons
B. neutrons
C. electrons
D. both A and C
CHAPTER
4
The Structure of the Atom
Chapter Assessment
Lithium has an atomic mass of 6.941 and two
isotopes, one with 6 neutrons and one with 7
neutrons. Which isotope is more abundant?
A. 6Li
B. 7Li
C. Both isotopes occur equally.
D. unable to determine
CHAPTER
4
The Structure of the Atom
Chapter Assessment
What happens when an element emits
radioactive particles?
A. It gains energy.
B. It gains neutrons.
C. It loses stability.
D. It loses energy.
CHAPTER
4
The Structure of the Atom
Standardized Test Practice
What is the smallest particle of an element that
still retains the properties of that element?
A. proton
B. atom
C. electron
D. neutron
CHAPTER
4
The Structure of the Atom
Standardized Test Practice
How many neutrons, protons, and electrons
does 12454Xe have?
A. 124 neutrons, 54 protons, 54 electrons
B. 70 neutrons, 54 protons, 54 electrons
C. 124 neutrons, 70 protons, 54 electrons
D. 70 neutrons, 70 protons, 54 electrons
CHAPTER
4
The Structure of the Atom
Standardized Test Practice
The primary factor in determining an atom's
stability is its ratio of neutrons
to ____.
A. protons
B. electrons
C. alpha particles
D. isotopes
CHAPTER
4
The Structure of the Atom
Standardized Test Practice
What is the densest region of an atom?
A. electron cloud
B. nucleus
C. isotopes
D. atomic mass
CHAPTER
4
The Structure of the Atom
Standardized Test Practice
Why are electrons attracted to the cathode in a
cathode ray tube?
A. The cathode is more stable.
B. The cathode has a positive charge.
C. The cathode has a negative charge.
D. The cathode has no charge.
This slide is intentionally blank.