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Chemistry: Matter and Change

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Title: Chemistry: Matter and Change


1
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2
Chapter Menu
The Structure of the Atom
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 or folder tab to view the
corresponding slides.
Exit
3
Section 4-1
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
4
Section 4-1
Section 4.1 Early Ideas About Matter (cont.)
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.
5
Section 4-1
Greek Philosophers (cont.)
  • 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.

6
Section 4-1
Greek Philosophers (cont.)
  • Democritus (460370 B.C.) was the first person to
    propose the idea that matter was not infinitely
    divisible, but made up of individual particles
    called atomos.
  • Aristotle (484322 B.C.) disagreed with
    Democritus because he did not believe empty space
    could exist.
  • Aristotles views went unchallenged for 2,000
    years until science developed methods to test the
    validity of his ideas.

7
Section 4-1
Greek Philosophers (cont.)
8
Section 4-1
Greek Philosophers (cont.)
  • John Dalton revived the idea of the atom in the
    early 1800s based on numerous chemical reactions.
  • Daltons atomic theory easily explained
    conservation of mass in a reaction as the result
    of the combination, separation, or rearrangement
    of atoms.

9
Section 4-1
Greek Philosophers (cont.)
10
Section 4-1
Section 4.1 Assessment
Who was the first person to propose the idea that
matter was not infinitely divisible?
A. Aristotle B. Plato C. Dalton D. Democritus
  1. A
  2. B
  3. C
  4. D

11
Section 4-1
Section 4.1 Assessment
Daltons theory also conveniently explained what?
A. the electron B. the nucleus C. law of
conservation of mass D. law of Democritus
  1. A
  2. B
  3. C
  4. D

12
End of Section 4-1
13
Section 4-2
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
14
Section 4-2
Section 4.2 Defining the Atom (cont.)
atom cathode ray electron nucleus proton neutron
An atom is made of a nucleus containing protons
and neutrons electrons move around the nucleus.
15
Section 4-2
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.

16
Section 4-2
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.

17
Section 4-2
The Electron (cont.)
  • This figure shows a typical cathode ray tube.

18
Section 4-2
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 particlethe
    electron

19
Section 4-2
The Electron (cont.)
  • In the early 1910s, Robert Millikan used the
    oil-drop apparatus shown below to determine the
    charge of an electron.

20
Section 4-2
The Electron (cont.)
  • Charges change in discrete amounts1.602 ? 1019
    coulombs, the charge of one electron (now
    equated to a single unit, 1).
  • With the electrons charge and charge-to-mass
    ratio known, Millikan calculated the mass of a
    single electron.

21
Section 4-2
The Electron (cont.)
  • Matter is neutral.
  • J.J. Thomson's plum pudding model of the atom
    states that the atom is a uniform, positively
    changed sphere containing electrons.

22
Section 4-2
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.

23
Section 4-2
The Nucleus (cont.)
  • Although most of the alpha particles went through
    the gold foil, a few of them bounced back, some
    at large angles.

24
Section 4-2
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.

25
Section 4-2
The Nucleus (cont.)
  • The repulsive force between the positively
    charged nucleus and positive alpha particles
    caused the deflections.

26
Section 4-2
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 atoms mass.

27
Section 4-2
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.

28
Section 4-2
The Nucleus (cont.)
  • Scientists have determined that protons and
    neutrons are composed of subatomic particles
    called quarks.

29
Section 4-2
The Nucleus (cont.)
  • Chemical behavior can be explained by considering
    only an atom's electrons.

30
Section 4-2
Section 4.2 Assessment
Atoms are mostly ____. A. positive B. negative
C. solid spheres D. empty space
  1. A
  2. B
  3. C
  4. D

31
Section 4-2
Section 4.2 Assessment
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
  1. A
  2. B
  3. C
  4. D

32
End of Section 4-2
33
Section 4-3
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.

34
Section 4-3
Section 4.3 How Atoms Differ (cont.)
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 isotopes mass number
atomic mass unit (amu) atomic mass
The number of protons and the mass number define
the type of atom.
35
Section 4-3
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
    elements atomic number.

36
Section 4-3
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.

37
Section 4-3
Isotopes and Mass Number (cont.)
  • The relative abundance of each isotope is usually
    constant.
  • Isotopes containing more neutrons have a greater
    mass.
  • Isotopes have the same chemical behavior.
  • The mass number is the sum of the protons and
    neutrons in the nucleus.

38
Section 4-3
Isotopes and Mass Number (cont.)
39
Section 4-3
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.

40
Section 4-3
Mass of Atoms (cont.)
  • The atomic mass of an element is the weighted
    average mass of the isotopes of that element.

41
Section 4-3
Section 4.3 Assessment
An unknown element has 19 protons, 19 electrons,
and 3 isotopes with 20, 21 and 22 neutrons. What
is the elements atomic number? A. 38 B. 40
C. 19 D. unable to determine
  1. A
  2. B
  3. C
  4. D

42
Section 4-3
Section 4.3 Assessment
Elements with the same number of protons and
differing numbers of neutrons are known as what?
A. isotopes B. radioactive C. abundant
D. ions
  1. A
  2. B
  3. C
  4. D

43
End of Section 4-3
44
Section 4-4
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
45
Section 4-4
Section 4.4 Unstable Nuclei and Radioactive
Decay (cont.)
radioactivity radiation nuclear
reaction radioactive decay alpha radiation
alpha particle nuclear equation beta
radiation beta particle gamma rays
Unstable atoms emit radiation to gain stability.
46
Section 4-4
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.

47
Section 4-4
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.

48
Section 4-4
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.

49
Section 4-4
Radioactive Decay (cont.)
  • The figure shown below is a nuclear equation
    showing the radioactive decay of radium-226 to
    radon-222.
  • The mass is conserved in nuclear equations.

50
Section 4-4
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.

51
Section 4-4
Radioactive Decay (cont.)
52
Section 4-4
Radioactive Decay (cont.)
  • Gamma rays are high-energy radiation with no mass
    and are neutral.
  • Gamma rays account for most of the energy lost
    during radioactive decay.

53
Section 4-4
Radioactive Decay (cont.)
  • 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 naturemost have already decayed to
    stable forms.

54
Section 4-4
Section 4.4 Assessment
A reaction that changes one element into another
is called what? A. chemical reaction B. beta
radiation C. nuclear reaction D. physical
reaction
  1. A
  2. B
  3. C
  4. D

55
Section 4-4
Section 4.4 Assessment
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.
  1. A
  2. B
  3. C
  4. D

56
End of Section 4-4
57
Resources Menu
Chemistry Online Study Guide Chapter
Assessment Standardized Test Practice Image
Bank Concepts in Motion
58
Study Guide 1
Section 4.1 Early Ideas About Matter
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 Daltons atomic theory is based on numerous
    scientific experiments.

59
Study Guide 2
Section 4.2 Defining the Atom
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.

60
Study Guide 3
Section 4.3 How Atoms Differ
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.

61
Study Guide 4
Section 4.4 Unstable Nuclei and Radioactive
Decay
Key Concepts
  • Chemical reactions involve changes in the
    electrons surrounding 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 atoms nucleus
    determines its stability.

62
Chapter Assessment 1
Whose work led to the modern atomic theory?
A. Dalton B. Rutherford C. Einstein
D. Aristotle
  1. A
  2. B
  3. C
  4. D

63
Chapter Assessment 2
Which particle is not found in the nucleus of an
atom? A. neutron B. proton C. gamma ray
D. electron
  1. A
  2. B
  3. C
  4. D

64
Chapter Assessment 3
Two isotopes of an unknown element have the same
number of A. protons B. neutrons
C. electrons D. both A and C
  1. A
  2. B
  3. C
  4. D

65
Chapter Assessment 4
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
  1. A
  2. B
  3. C
  4. D

66
Chapter Assessment 5
What happens when an element emits radioactive
particles? A. It gains energy. B. It gains
neutrons. C. It loses stability. D. It loses
energy.
  1. A
  2. B
  3. C
  4. D

67
STP 1
What is the smallest particle of an element that
still retains the properties of that element?
A. proton B. atom C. electron D. neutron
  1. A
  2. B
  3. C
  4. D

68
STP 2
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
  1. A
  2. B
  3. C
  4. D

69
STP 3
The primary factor in determining an atom's
stability is its ratio of neutrons to ____.
A. protons B. electrons C. alpha
particles D. isotopes
  1. A
  2. B
  3. C
  4. D

70
STP 4
What is the densest region of an atom?
A. electron cloud B. nucleus C. isotopes
D. atomic mass
  1. A
  2. B
  3. C
  4. D

71
STP 5
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.
  1. A
  2. B
  3. C
  4. D

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CIM
Table 4.3 Properties of Subatomic
Particles Figure 4.12 Rutherford's
Experiment Figure 4.14 Features of an
Atom Figure 4.21 Types of Radiation
91
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