The document presents a detailed overview of the history and development of atomic theory, highlighting key figures such as Democritus, Dalton, Thomson, Rutherford, Bohr, and Schrödinger. It outlines significant experiments and models that contributed to our understanding of atomic structure, including the cathode ray experiment, the gold foil experiment, and the evolution from the plum pudding model to the quantum mechanical model. The goals of the lesson include constructing models based on these theories and understanding the contemporary view of atomic structure.

1. 9/26/2024
1. What are the 3 subatomic particles?
The 3 subatomic particles are ……..
1. What is the charge for each particle?
For the ________ the charge is ________.
For the ________ the charge is ________.
For the ________ the charge is ________.
1. What does the period number tell you about
an atom?
From the period number I can determine the
…………
Do Now Agenda
• Do Now
• History of the Atom
• Cathode Ray experiment
• DOL
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TEKS
Chem 6.A. Construct models using Dalton's Postulates, Thomson's
discovery of electron properties, Rutherford's nuclear atom, Bohr's
nuclear atom, and Heisenberg's Uncertainty Principle to show the
development of modern atomic theory over time;
Chem 6.B. describe the structure of atoms and ions, including the
masses, electrical charges, and locations of protons and neutrons
in the nucleus and electrons in the electron cloud;
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Learning Objective
• Students will be able to construct models using Dalton's
Postulates, Thomson's discovery of electron properties,
Rutherford's nuclear atom, Bohr's nuclear atom, and Heisenberg's
Uncertainty Principle to show the development of modern atomic
theory over time;
• Students will be able to describe the structure of atoms and ions,
including the masses, electrical charges, and locations of protons
and neutrons in the nucleus and electrons in the electron cloud;
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2. 9/26/2024
Who are these men?
In this lesson, we’ll learn
about the men whose
quests for knowledge
about the fundamental
nature of the universe
helped define our views.
Schrödinger
Heisenberg
Bohr
Rutherford
Thomson
Dalton
Democritus
Name
Time
Frame
Key
Points
describe
Model
Be ready to
write
relevant
information
on your
content
frame
table. Keep
up and stay
alert!
Democritus
460 – 370 B.C.
• There are various basic elements
from which all matter is made
• Everything is composed of small
atoms moving in a void
• Some atoms are round, pointy,
oily, have hooks, etc. to account
for their properties
• Ideas rejected by leading
philosophers because void = no
existence
Atomos
• His theory: Matter
could not be divided
into smaller and smaller
pieces forever,
eventually the smallest
possible piece would be
obtained.
• This piece would be
indivisible.
• He named the smallest
piece of matter
“atomos,” meaning “not
to be cut.”
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3. 9/26/2024
First Concept of an Atom
Draw a visual representation of
how Democritus’ concept of
atoms differs from what we
know today. Label the
‘Democritus atom’ and the
‘Modern atom’ and explain the
difference.”
Dalton’s Model
• In the early
1800s, the
English Chemist
John Dalton
performed a
number of
experiments that
eventually led to
the acceptance of
the idea of atoms.
John Dalton
1766-1844
• Introduced his ideas in 1803
• Each element is composed of extremely
small particles called atoms
• All the atoms of a given element are
identical, but they differ from those of
any other element
• Atoms are neither created nor
destroyed in any chemical reaction
• A given compound always has the same
relative numbers and kinds of atoms
Dalton’s Theory
• He deduced that all
elements are composed of
atoms. Atoms are
indivisible and
indestructible particles.
• Atoms of the same
element are exactly alike.
• Atoms of different
elements are different.
• Compounds are formed by
the joining of atoms of two
or more elements.
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4. 9/26/2024
HOT: Why is Dalton’s Model important in understanding
chemical compounds?
The red
and blue
solid
circles
represent
atoms or
elements.
Combined
they are
called
compound.
Thomson’s Plum Pudding
Model
• In 1897, the
English scientist
J.J. Thomson
provided the
first hint that
an atom is made
of even smaller
particles.
J.J. Thomson
1856-1940
• Discovered electron
1897 – Cathode Ray
Experiment
• Plum Pudding model
1904
– Electrons in a soup of
positive charges
• Discovered isotopes
1913
Thomson Model
• He proposed a model
of the atom that is
sometimes called the
“Plum Pudding” model.
• Atoms were made from
a positively charged
substance with
negatively charged
electrons scattered
about, like raisins in a
pudding.
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5. 9/26/2024
JJ Thomson’s Ideas
“What are the
‘positive and
negative forces’
Thomson
referred to in his
research?” Hint:
How does something
stick to a whiteboard?
Cathode Ray Tube Experiment
• Based on
the
experiment,
how do we
know that
electrons
are
negatively
charged?
Cathode Ray Tube Experiment
HOT: Explain
the cathode ray
tube experiment
in at least 2
complete
sentences.
Thomson Model
• Thomson studied the
passage of an electric
current through a
gas.
• As the current
passed through the
gas, it gave off rays
of negatively charged
particles.
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6. 9/26/2024
Thomson Model
• This surprised
Thomson,
because the
atoms of the gas
were uncharged.
Where had the
negative charges
come from?
Where did
they come
from?
Thomson concluded that the
negative charges came from
within the atom.
A particle smaller than an atom
had to exist.
The atom was divisible!
Thomson called the negatively
charged “corpuscles,” today known
as electrons.
Since the gas was known to be
neutral, having no charge, he
reasoned that there must be
positively charged particles in the
atom.
But he could never find them.
Plum Pudding Model
Draw the Plum
Pudding Model and
label the positive and
negative parts.
Compare this model
to a modern
understanding of the
atom. What key
feature is missing?
DOL
• Given a set of 5 questions, construct
models using Dalton's Postulates,
Thomson's discovery of electron
properties, Rutherford's nuclear atom,
Bohr's nuclear atom, and Heisenberg's
Uncertainty Principle to show the
development of modern atomic theory
over time;
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7. 9/26/2024
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Closing Procedure
Closing Procedure
❑ Make your area neat
❑ Wipe down desk
❑ Stack binders neatly [Notebook person
collects them]
❑ Return pencils in bin
❑ Grab Backpack & Phone
❑ Leave the classroom C1W5L2
Atomic History
&
Gold Foil Experiment
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MRS Icons
MRS Icons
36
5 Minutes
Opening Procedure
Opening Procedure
❑ Find your seat (front first)
❑ Make your area neat
❑ Get your Binder[Notebook person]
❑ Sharpen your pencils
❑ Take out your computer
❑ Prepare for Do Now (graded)
❑ Put your phone in your pouch
❑ Backpacks in the front of the classroom
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8. 9/26/2024
Agenda
• Do Now
• History of the Atom
• Gold Foil Experiment
• DOL
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Do Now
Based on your prior knowledge, draw a
modern model of an atom and label its parts.
After drawing, answer: Where do you think
most of the mass of the atom is located, and
why?
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• Ok, lets talk
about the next
scientist!
• Rutherford’s
experiment
Involved firing
a stream of
tiny positively
charged
particles at a
thin sheet of
gold foil (2000
atoms thick)
Schrödinger
Heisenberg
Bohr
Rutherford
Thomson
Dalton
Democritus
Name
Time
Frame
Key
Points
describe
Model
Gold Foil Experiment
How did the
deflection patterns
observed in the
gold foil
experiment lead
to the conclusion
that the atom has
a small, dense
nucleus
surrounded by
mostly empty
space?
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9. 9/26/2024
Rutherford Model
Based on
Rutherford’s model,
why do most alpha
particles pass
through the atom
without deflection,
while a few are
deflected at large
angles?
Gold Foil Experiment
– Most of the positively
charged “bullets”
passed right through
the gold atoms in the
sheet of gold foil
without changing course
at all.
– Some of the positively
charged “bullets,”
however, did bounce
away from the gold
sheet as if they had hit
something solid. He
knew that positive
charges repel positive
charges.
Alpha Particle Experiment
What conclusions
about the structure of
the atom were drawn
from the results of the
alpha particle
experiment, and how
did this experiment
challenge the
previous plum
pudding model?
Alpha Particle Experiment
• This could only mean that the gold atoms in the sheet
were mostly open space. Atoms were not a pudding
filled with a positively charged material.
• Rutherford concluded that an atom had a small, dense,
positively charged center that repelled his positively
charged “bullets.”
• He called the center of the atom the “nucleus”
• The nucleus is tiny compared to the atom as a whole.
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10. 9/26/2024
Ernest Rutherford
1871-1937
• Nucleus Theory 1910
– alpha particle gold foil
experiment
• An atom’s mass is
mostly in the nucleus
• The nucleus has a
positive charge
(Moseley)
• Electrons in fixed orbit
Rutherford Model
How did Rutherford’s
model change our
understanding of the
atom, particularly
regarding the
location of positive
charge and the role
of empty space?
Bohr Model
• In 1913, the
Danish scientist
Niels Bohr
proposed an
improvement. In
his model, he
placed each
electron in a
specific energy
level.
Bohr Model
• According to Bohr’s
atomic model, electrons
move in definite orbits
around the nucleus,
much like planets circle
the sun.
• These orbits, or energy
levels, are located at
certain distances from
the nucleus.
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11. 9/26/2024
Niels Bohr
1885-1962
• Planetary Model 1913
– Nucleus surrounded by
orbiting electrons at
different energy levels
– Electrons have definite
orbits
• Utilized Planck’s Quantum
Energy theory
• Worked on the
Manhattan Project (US
atomic bomb)
Bohr’s Model
Bohr Model for Nitrogen
HOT: How does the
Bohr model explain the
arrangement of
nitrogen’s electrons in
specific energy levels,
and why are only two
electrons placed in the
first energy level?
Rutherford v Bohr
Which model of the
atom—Rutherford’s or
Bohr’s—better explains
the behavior of
electrons in modern
chemistry, and why?
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12. 9/26/2024
Wave Model
Ernst Schrödinger 1887-1961
• Quantum Mechanical
Model 1926
– Electrons are in probability
zones called “orbitals”, not
orbits and the location
cannot be pinpointed
– Electrons are particles and
waves at the same time
– Developed quantum numbers
based on theories of
Einstein and Planck
Werner Heisenberg 1901-1976
Interference: Waves or Particles?
How does the double-slit
experiment show that
electrons behave like
waves?
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Draw the pattern you would expect to see if
electrons behaved only like particles when
passing through the two slits. Then explain it
to your group.
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13. 9/26/2024
The Wave Model
• Today’s atomic
model is based on
the principles of
wave mechanics.
• According to the
theory of wave
mechanics, electrons
do not move about
an atom in a definite
path, like the
planets around the
sun.
The Wave Model
• In fact, it is impossible to determine
the exact location of an electron. The
probable location of an electron is
based on how much energy the
electron has.
• According to the modern atomic
model, at atom has a small positively
charged nucleus surrounded by a large
region in which there are enough
electrons to make an atom neutral.
Electron Cloud:
• A space in which electrons are
likely to be found.
• Electrons whirl about the
nucleus billions of times in one
second
• They are not moving around in
random patterns.
• Location of electrons depends
upon how much energy the
electron has.
Electron Cloud:
Depending on their energy they are locked into a
certain area in the cloud.
Electrons with the lowest energy are found in
the energy level closest to the nucleus
Electrons with the highest energy are found in
the outermost energy levels, farther from the
nucleus.
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Orbital Size and Energy Levels:
Growing with Distance
How do the
sizes and
shapes of
orbitals change
as you move to
higher energy
levels in an
atom?
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Why do p orbitals have
different orientations (px,
py, pz), and how does this
relate to the way electrons
move in three dimensions?
Hint: Why
would it
be useful
for
electrons
to have
orbitals
oriented
along
each
axis?
Orbitals
How do the shapes
of different orbitals
(like s and p orbitals)
relate to the
probability of finding
an electron near the
nucleus?
Quantum Mechanical Theory
Electron in a Hydrogen atom
HOT: How does
quantum mechanical
theory describe the
behavior of electrons in
a hydrogen atom, and
how is this different
from previous atomic
models?
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15. 9/26/2024
Electron
Cloud
Orbit
Nucleus
Electron
Indivisible
X
Greek
X
Dalton
X
Thomson
X
X
Rutherford
X
X
X
Bohr
X
X
X
Wave
DOL
• Given a set of 5 questions, students will
be able to identify and predict the
properties of elements in the periodic
table, including their group and period,
atomic number, and various periodic
trends.
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Closing Procedure
Closing Procedure
❑ Make your area neat
❑ Wipe down desk
❑ Stack binders neatly [Notebook person
collects them]
❑ Return pencils in bin
❑ Grab Backpack & Phone
❑ Leave the classroom
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