Chapter Menu

1
Chapter Menu
Chapter Introduction Lesson 1 Discovering Parts
of an Atom Lesson 2 Protons, Neutrons, and
Electrons How Atoms Differ Chapter Wrap-Up
2
Chapter Introduction

• What are atoms, and what are they made of?

3
Chapter Introduction

• What do you think?

Before you begin, decide if you agree or disagree
with each of these statements. As you view this
presentation, see if you change your mind about
any of the statements.
4
Chapter Introduction
Do you agree or disagree?

• 1. The earliest model of an atom contained only
  protons and electrons.
• 2. Air fills most of an atom.
• 3. In the present-day model of the atom, the
  nucleus of the atom is at the center of an
  electron cloud.

5
Chapter Introduction
Do you agree or disagree?

• 4. All atoms of the same element have the same
  number of protons.
• 5. Atoms of one element cannot be changed into
  atoms of another element.
• 6. Ions form when atoms lose or gain electrons.

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Lesson 1 Reading Guide - KC
Discovering Part of an Atom

• What is an atom?
• How would you describe the size of an atom?
• How has the atomic model changed over time?

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Lesson 1 Reading Guide - Vocab
Discovering Part of an Atom

• atom
• electron
• nucleus
• proton

• neutron
• electron cloud

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Lesson 1-1
Early Ideas About Matter

• Democritus (460370 BC) believed that matter is
  made of small, solid objects called atomos, from
  which the English word atom is derived.

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Lesson 1-1
Early Ideas About Matter (cont.)

• Aristotle (384322 BC) did not believe that empty
  space exists, but instead believed that all
  matter is made of fire, water, air, and earth.
• Because Aristotle was so influential, his ideas
  were accepted and Democrituss ideas about atoms
  were not studied again for more than 2,000 years.

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Lesson 1-2
Daltons Atomic Model

• John Dalton combined data from his own scientific
  research with data from the research of other
  scientists to propose a new atomic theory.

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Lesson 1-3
The Atom

• An atom is the smallest piece of an element that
  still represents that element.

What is a copper atom?
12
Lesson 1-3
The Atom (cont.)

• Atoms of different elements are different sizes,
  but all are very, very small.
• You cannot see atoms with just your eyes or even
  with most microscopes.

How would you describe the size of an atom?
13
Lesson 1-3
The Atom (cont.)

• The 1981 invention of a high-powered microscope,
  called a scanning tunneling microscope (STM),
  enabled scientists to see individual atoms for
  the first time.
• Scientists have learned that atoms are not the
  smallest particles of matter.

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Lesson 1-4

• Following his experiments with cathode ray tubes,
  scientist J.J. Thomson concluded that cathode
  rays were made of small, negatively charged
  particles which he called electrons.

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Lesson 1-4
ThomsonDiscovering Electrons

• An electron is a particle with one negative
  charge (1).

electron from Greek electron, means amber, the
physical force so called because it first was
generated by rubbing amber. Amber is a fossilized
substance produced by trees.
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Lesson 1-4
ThomsonDiscovering Electrons (cont.)

• Because atoms are neutral, or not electrically
  charged, Thomson proposed that atoms also must
  contain a positive charge that balances the
  negatively charged electrons.
• Thomsons proposed atom was a sphere with a
  positive charge evenly spread throughout and
  negatively charged electrons within it.

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Lesson 1-4

• Thomsons model of the atom contained a sphere of
  positive charge with negatively charged electrons
  within it.

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Lesson 1-5
RutherfordDiscovering the Nucleus

• Scientist Ernest Rutherford set up experiments to
  test Thomsons atomic model and to learn more
  about what atoms contain.

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Lesson 1-5

• Rutherford expected the positive alpha particles
  to travel straight through the foil without
  changing direction.

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Lesson 1-5

• Some alpha particles traveled in a straight path,
  as expected. But some changed direction, and some
  bounced straight back.

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Lesson 1-5
RutherfordDiscovering the Nucleus (cont.)
Given the results of the gold foil experiment,
how do you think an actual atom differs from
Thomsons model?
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Lesson 1-5
RutherfordDiscovering the Nucleus (cont.)

• Rutherford concluded that most of an atoms mass
  and positive charge is concentrated in a small
  area in the center of the atom called the
  nucleus.
• Additional research showed that the positive
  charge in the nucleus was made of positively
  charged particles called protons.

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Lesson 1-5
RutherfordDiscovering the Nucleus (cont.)

• A proton is an atomic particle that has one
  positive charge (1).
• Negatively charged electrons move in the empty
  space surrounding the nucleus.

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Lesson 1-5

• Rutherfords model contains a small, dense,
  positive nucleus. Tiny, negatively charged
  electrons travel in empty space around the
  nucleus.

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Lesson 1-6
Discovering Neutrons

• James Chadwick discovered that, in addition to
  protons, the nucleus also contained neutrons.
• A neutron is a neutral particle that exists in
  the nucleus of an atom.

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Lesson 1-6
Bohrs Atomic Model

• Niels Bohr proposed that electrons move in
  circular orbits, or energy levels, around the
  nucleus.
• Electrons closer to the nucleus have less energy
  than electrons farther away from the nucleus.

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Lesson 1-6
Bohrs Atomic Model (cont.)

• More research showed that, although electrons
  have specific amounts of energy, energy levels
  are not arranged in circular orbits.
• When an electron moves from a higher energy level
  to a lower energy level, energy is
  releasedsometimes as visible light.

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Lesson 1-6

• In Bohrs model of the atom, electrons move in
  circular orbits around the atom.

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Lesson 1-6
Bohrs Atomic Model (cont.)
How did Bohrs model of the atom differ from
Rutherfords?
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Lesson 1-6
The Modern Atomic Model

• In the modern atomic model, electrons form an
  electron cloud.
• An electron cloud is an area around an atomic
  nucleus where an electron is most likely to be.

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Lesson 1-6

• In this atom, electrons are more likely to be
  found closer to the nucleus than farther away.

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Lesson 1-6
The Modern Atomic Model (cont.)
How has the model of the atom changed over time?
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Lesson 1-6
Quarks

• Protons and neutrons are made of smaller
  particles called quarks.
• Scientists theorize that there are six types of
  quarks up, down, charm, strange, top, and
  bottom.
• Protons are made of two up quarks and one down
  quark.

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Lesson 1-6
Quarks (cont.)

• Neutrons are made of two down quarks and one up
  quark.
• The current atomic model might change with the
  invention of new technology that aids the
  discovery of new information.

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Lesson 1 - VS

• If you were to divide an element into smaller and
  smaller pieces, the smallest piece would be an
  atom.
• Atoms are so small that they can be seen only by
  using very powerful microscopes.

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Lesson 1 - VS

• Scientists now know that atoms contain a dense,
  positive nucleus surrounded by an electron cloud.

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Lesson 1 LR1
Which term describes a particle with one negative
charge?
A. atom B. electron C. nucleus D. proton
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Lesson 1 LR2
Whose model of the atom contained a sphere of
positive charge with negatively charged electrons
within it?
A. Dalton B. Democritus C. Rutherford D. Thomson
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Lesson 1 LR3
Which term refers to an area around an atomic
nucleus where an electron is most likely to be?
A. electron cloud B. neutron C. nucleus
D. proton
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Lesson 1 - Now
Do you agree or disagree?

• 1. The earliest model of an atom contained only
  protons and electrons.
• 2. Air fills most of an atom.
• 3. In the present-day model of the atom, the
  nucleus of the atom is at the center of an
  electron cloud.

41
Lesson 2 Reading Guide - KC
Protons, Neutrons, and ElectronsHow Atoms Differ

• What happens during nuclear decay?
• How does a neutral atom change when its number of
  protons, electrons, or neutrons changes?

42
Lesson 2 Reading Guide - Vocab
Protons, Neutrons, and ElectronsHow Atoms Differ

• atomic number
• isotope
• mass number
• average atomic mass

• radioactive
• nuclear decay
• ion

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Lesson 2-1
The Parts of the Atom

• The mass of electrons is much smaller than the
  mass of protons or neutrons.
• Most of the mass of an atom is found in the
  nucleus.

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Lesson 2-1
Different ElementsDifferent Numbers of Protons

• The number of protons in an atom of an element is
  the elements atomic number.
• The atomic number is the whole number listed with
  each element on the periodic table.
• Atoms of different elements contain different
  numbers of protons.

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Lesson 2-1

• Different elements have different atomic numbers.

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Lesson 2-1
Different ElementsDifferent Numbers of Protons
(cont.)

• Neutral atoms of different elements also have
  different numbers of electrons.
• In a neutral atom, the number of electrons equals
  the number of protons therefore, the number of
  positive charges equals the number of negative
  charges.

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Lesson 2-2
Neutrons and Isotopes

• Atoms of the same element can have different
  numbers of neutrons.
• Isotopes are atoms of the same element that have
  different numbers of neutrons.
• Most elements have several isotopes.

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Lesson 2-2
Neutrons and Isotopes (cont.)
isotope from Greek isos, means equal and
topos, means place
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Lesson 2-2
Neutrons and Isotopes (cont.)

• The mass number of an atom is the sum of the
  number of protons and neutrons in an atom.
• Mass number number of protons number of
  neutrons
• An isotope is often written with the element name
  followed by the mass number.

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Lesson 2-2
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Lesson 2-2
Neutrons and Isotopes (cont.)

• The average atomic mass of an element is the
  average mass of the elements isotopes, weighted
  according to the abundance of each isotope.

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Lesson 2-4
Radioactivity

• Marie Curie called elements that spontaneously
  emit radiation radioactive.
• Henri Becquerel and Pierre and Marie Curie
  discovered that the radiation released by uranium
  was made of energy and particles.

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Lesson 2-4
Radioactivity (cont.)

• This radiation came from the nuclei of the
  uranium atoms.
• When uranium releases radiation, it changes to a
  different element.

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Lesson 2-4
Radioactivity (cont.)

• Nuclear decay is a process that occurs when an
  unstable atomic nucleus changes into another more
  stable nucleus by emitting radiation.
• Nuclear decay can produce three different types
  of radiationalpha particles, beta particles, and
  gamma rays.

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Lesson 2-4

• An alpha particle is made of two protons and two
  neutrons. When an atom releases an alpha
  particle, its atomic number decreases by two.

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Lesson 2-4

• When beta decay occurs, a neutron changes into a
  proton and a high-energy electron called a beta
  particle. The atomic number of an atom increases
  by one because it has gained a proton.

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Lesson 2-4

• Because gamma rays do not contain particles, the
  release of gamma rays does not change one element
  into another element.

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Lesson 2-4
Radioactivity (cont.)
What happens during radioactive decay?
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Lesson 2-4
Radioactivity (cont.)

• The energy released by radioactive decay can be
  both harmful and beneficial to humans.
• Radiation therapy can be beneficial to humans by
  destroying harmful cells such as cancer cells.

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Lesson 2-5
IonsGaining or Losing Electrons

• An ion is an atom that is no longer neutral
  because it has gained or lost electrons.
• An ion can be positively or negatively charged
  depending on whether it has lost or gained
  electrons.

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Lesson 2-5

• When a neutral atom loses one or more electrons,
  it has more protons than electrons and as a
  result, has a positive charge.
• An atom with a positive charge is called a
  positive ion.

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Lesson 2-5

• When a neutral atom gains one or more electrons,
  it now has more electrons than protons and as a
  result, has a negative charge.
• An atom with a negative charge is called a
  negative ion.

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Lesson 2-4
IonsGaining or Losing Electrons (cont.)
How does a neutral atom change when its number
of protons or electrons changes?
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Lesson 2 - VS

• Different elements contain different numbers of
  protons.

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Lesson 2 - VS

• Two isotopes of a given element contain
  different numbers of neutrons.

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Lesson 2 - VS

• When a neutral atom gains or loses an electron,
  it becomes an ion.

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Lesson 2 LR1
Where is most of the mass of an atom found?
A. electrons B. neutrons C. nucleus D. protons
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Lesson 2 LR2
Which term refers to the sum of the number of
protons and neutrons in an atom?
A. atomic number B. average atomic mass
C. isotope D. mass number
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Lesson 2 LR3
What term did Marie Curie use to describe
elements that spontaneously emit radiation?
A. ion B. isotopes C. nuclear decay
D. radioactive
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Lesson 2 - Now
Do you agree or disagree?
4. All atoms of the same element have the same
number of protons. 5. Atoms of one element cannot
be changed into atoms of another element. 6. Ions
form when atoms lose or gain electrons.
71
Chapter Review Menu
Key Concept Summary Interactive Concept
Map Chapter Review Standardized Test Practice
72
The BIG Idea

• An atom is the smallest unit of an element and is
  made mostly of empty space. It contains a tiny
  nucleus surrounded by an electron cloud.

73
Key Concepts 1
Lesson 1 Discovering Parts of the Atom

• If you were to divide an element into smaller and
  smaller pieces, the smallest piece would be an
  atom.
• Atoms are so small that they can be seen only by
  powerful scanning microscopes.
• The first model of the atom was a solid sphere.
  Now, scientists know that an atom contains a
  dense positive nucleus surrounded by an
  electron cloud.

74
Key Concepts 2
Lesson 2 Protons, Neutrons, and ElectronsHow
Atoms Differ

• Nuclear decay occurs when an unstable atomic
  nucleus changes into another more stable
  nucleus by emitting radiation.
• Different elements contain different numbers of
  protons. Two isotopes of the same element
  contain different numbers of neutrons. When a
  neutral atom gains or loses an electron, it
  becomes an ion.

75
Chapter Review MC1
Which term describes a neutral particle that
exists in the nucleus of an atom?
A. atom B. electron C. neutron D. proton
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Chapter Review MC2
Who discovered that, in addition to protons, the
nucleus also contained neutrons?
A. Thomson B. Rutherford C. Chadwick D. Bohr
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Chapter Review MC3
Protons and neutrons are made of smaller
particles called what?
A. electron cloud B. isotope C. nucleus
D. quarks
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Chapter Review MC4
Which term refers to the process that occurs when
an unstable atomic nucleus changes into another
more stable nucleus by emitting radiation?
A. radiation B. radioactivity C. nuclear decay
D. radiation therapy
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Chapter Review MC5
Which describes an atom with a positive charge?
A. positive ion B. negative ion C. isotope D. quar
ks
80
Chapter Review STP1
Which term refers to the smallest piece of an
element that still represents that element?
A. quark B. nucleus C. electron D. atom
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Chapter Review STP2
Who concluded that most of an atoms mass and
positive charge is concentrated in the nucleus?
A. Aristotle B. Bohr C. Chadwick D. Rutherford
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Chapter Review STP3
Which is an atomic particle that has one positive
charge?
A. proton B. nucleus C. neutron D. electron
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Chapter Review STP4
Which term refers to an atom that is no longer
neutral because it has gained or lost electrons?
A. ion B. isotope C. neutron D. proton
84
Chapter Review STP5
Which refers to the average mass of an elements
isotopes, weighted according to the abundance of
each isotope?
A. atomic number B. mass number C. relative
mass D. average atomic mass