Download Chapter 4: The Structure of the Atom

Chapter 4: The Structure of the
Atom
Early Theories of Matter
 Development of Atomic Theory
 Early Philosophers thought
matter could be divided into
smaller pieces.
Democritus:
 Matter was made of atomos
 Matter is composed of
empty space
 Different kinds of atoms
have different shapes and
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sizes and therefore,
properties.
Aristotle:
Criticized Democritus
He did not believe in empty
space concept.


Dalton:
 Began modern atomic theory
based on Democritus’s ideas
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 All matter is made of
atoms
 All atoms of a given
element are identical
 Atoms cannot be created,
divided, or destroyed
 Atoms combine in whole
number ratios to form
compounds
 In a chemical reaction,
atoms are separated,
combined, or rearranged
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Chapter 4 Guided Reading
pp. 106-110 Defining the Atom
1. Describe a typical cathode ray tube.
2. What did Sir William Crookes conclude?
3. What did JJ Thompson find?
4. What did Millikan discover?
5. If an electron has a negative charge and such little mass, how is
matter neutral? Also, how does an atom have mass?
6. Describe the plum pudding model.
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pp.111-113 The Nucleus
1. Explain Rutherford’s gold foil experiment using the text and the
following illustrations.
2. What is an alpha particle?
3. What did Rutherford mean when he said an atom is mostly
empty space?
4. How did Rutherford’s nuclear model help to explain that matter
is neutral?
5. What part of the atom is Rutherford credited with finding?
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p.114 Completing the Model of the Atom
1. Who was credited with defining the proton?
2. Who was credited with defining the neutron?
3. Copy Table 4-3 here from page 114. It is CRITICAL that you
MEMORIZE this information.
4. Where is the majority (99.97%) of an atom’s mass?
5. Why do you think that Rutherford said an atom is composed
mostly of empty space?
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The Modern Atom:
Atom: The smallest particle of an
element that retains properties
of that element.
Ex: Gold and Gold dust
How small is an atom?
World population
6,000,000,000
Atoms in a penny
29,000,000,000,000,000,000,00
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STM (Scanning Tunneling
Microscope) Images @
http://www.almaden.ibm.com/vis/
stm/hexagone.html
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What should you know about an
atom?
This represents a block from
your periodic table.
12.0111
Mass #
C
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Atomic #
http://www.chemicool.com/
Mass # = protons + neutrons
Atomic # = protons AND
electrons
In a neutral atom, the number of
protons = the number of
electrons.
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How do you find the number of
neutrons?
Sample:
Element Bromine Calcium Manganese Tin
Atomic
#
Mass #
# p+
# n0
#e-
Nuclear notation: Another way of
displaying element information.
Ex: 39
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p =
K
e =
n =
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Elements with the same atomic
#, but with different mass
numbers.
So, what does that tell you?
Example:
C-14
C-12
C-13
More examples:
Isotope
Atomic #
Mass #
43
92
96
Molybdenum
Nuclear
notation
Mn-55
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Isotopes and Weighted Averages:
All elements have isotopes.
Different isotopes are
found in varying amounts as
indicated by % abundance.
The atomic mass on the
periodic table is an average
based on the % abundance of
all isotopes/element.
There are radioactive
isotopes=radioisotopes. Ex:
Polonium Po
Formula for calculating
weighted average = (%
abundance * mass of isotope
1) + (% abundance * mass of
isotope 2)…
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Example problem:
Calculate the average
atomic mass of naturally
occurring Copper given the
following data.
Cu-63 mass= 62.929598amu
Occurs 69.17%
Cu-65 mass= 64.927793amu
Occurs 30.83%
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A positively (CATION) or
negatively (ANION) charged
particle.
How does this happen?
Examples:
1) F-1 p=
2) Mg2+
e=
p=
n=
e=
n=
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3) Fill in the missing blanks.
Symbol Na
As
Ion
1+
3charge
# p+
4
#e2
10
#n0
12
42
10
Atomic
9
#
Mass
9
#
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Radioactivity and Nuclear
Chemistry:
 Nuclear reaction: involve a
change in the atom’s nucleus.
 Radioactivity: The process
where some substances
spontaneously emit radiation.
 When radioactive
substances emit radiation,
they can transmutate: change
into a different element.
 Why do atoms emit
radiation?
 Because their nuclei are
unstable, so they emit energy
and undergo radioactive decay.
 Types of Radiation:
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 Use Tables N: What mode
of decay select radioisotopes
undergo.
 Use Table O: Symbols for
decay modes
 Alpha α = He
 Example of nuclear
equation:
 Beta β = beta negative = e
 Example:
Beta positive = positron = e
 Example:
 Gamma Υ = Υ
 Example:
 Experiment for detecting
type of radiation:
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 Nuclear Stability: To
determine an atom’s stability,
you must find the neutron to
proton ratio. Too many or too
few neutrons make an atom
unstable. A 1:1 ratio is most
stable.
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