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CHAPTER 5
Early Atomic Theory and Structure
5.1 EARLY THOUGHTS
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The early Greek Philosophers
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Earth, Air, Water, Fire
Democritus
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All matter made of atoms
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Atomos, Greek – indivisible
Tiny indivisible particles
5.2 DALTON’S MODEL OF THE ATOM
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Page 82 – What are the 6 big ideas of Dalton’s
theory?
What ideas are still valid? Not valid?
Which ideas could be made valid with a little
modification?
5.3 COMPOSITION OF COMPOUNDS
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Law of Definite Composition
Compounds always contains two or more elements
chemically combined in a definite proportion by mass
 Examples:
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Law of Multiple Proportions
Atoms of two or more elements may combine in
different ratios to produce more than one compound
 Examples:
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See pg 84, Table 5.1 for more examples
5.4 THE NATURE OF ELECTRIC CHARGE
Charges are of two types: Positive and Negative
 Unlike charges attract and like charges repel
 Charges may be transferred by contact or
induction
 The closer two object are, the greater the force of
attraction
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F = (kq1q2)/r2
q are the charges, r is distance between charges, k is a
constant
 DO NOT have to know the formula
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5.5 DISCOVERY OF IONS
Michael Faraday – some substances conduct
electricity in solution, others decompose when
electricity was passed through compounds
 Also noticed some atoms of elements are
attracted to positive end of electrode, while
others were attracted to negative end
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Called these “ions” for the Greek for “wanderer”
Svante Arrhenius – extended Faraday’s work
Positive ions  positive terminal (cathode)  cation
 Negative ions  negative terminal (anode)  anion
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G. J. Stoney – predicted the existence of the
electron but couldn’t prove it… who did?
5.6 SUBATOMIC PARTICLES OF THE ATOM
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Electrons
Crookes and JJ Thomson
 Millikan
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Protons
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Rutherford and Goldstein
Thomson Model replaces Dalton Model
 Neutron
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Chadwick
Know the relative size, location, symbol, and
charge of the subatomic particles
5.7 THE NUCLEAR ATOM
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Henri Becquerel – discovered radioactivity
Rutherford used Becquerel’s work to generate the
alpha particle stream in his “gold foil experiment”
 Led to Chadwick’s work which discovered the
neutron
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How do you determine the number of protons and
electrons in a neutral atom?
5.8 ISOTOPES OF THE ELEMENTS
Isotopes – atoms of an element that have the
same number of protons and a differing number
of neutrons
 Mass number = protons + neutrons
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How many protons, neutrons, and electrons are
in each of Hydrogen’s isotopes?
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Refer to page 90, Figure 5.8
How do you read isotope notation?
5.8 PRACTICE PROBLEMS
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5.3 How many protons, neutrons, and electrons
are in each of the isotopes?
16 O
80
235
64
8
35 Br
92 U
29 Cu
5.4 What are the atomic number, mass number,
and name of the following elements?
 9 electrons
 24 protons and 28 neutrons
 197 79 X
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5.9 ATOMIC MASS
Atomic Mass Unit (amu) – exactly 1/12 the mass
of a Carbon-12 atom.
 Atomic Mass – average relative mass of the
isotopes of an element
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Atomic Mass = Σ(mass of isotope x % abundance)
5.9 PRACTICE PROBLEMS
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5.5 Silver occurs as two isotopes with atomic
masses 106.9041 amu and 108.9047 amu,
respectively. The first isotope represents 51.82%
and the second represents 48.18%. Determine the
average atomic mass of silver.
CHAPTER 5 HOMEWORK
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Required
Paired and Additional Exercises
 1-42 (even)
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Optional
Same as above
 Odd
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