Atomic Theory
Let’s Take a Trip Through Time!
Atomic Theories Timeline
Name
Time
Frame
Key
Points
Democritus
Dalton
Thompson
Rutherford
Bohr
Schrödinger
Heisenberg
Copy all notes in red on
your graphic organizer
through slide 17!
Democritus
400 B.C.
• There are various basic
elements from which all
matter is made
• Everything is composed
of small atoms
• Some atoms are round,
pointy, oily, have hooks,
etc. to account for their
properties
Democritus’s Model
John Dalton
• 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
Dalton’s Model
J.J. Thompson
1904
• Discovered electron
(negative particle) in
the Cathode Ray
Experiment
• Plum Pudding model
1904
– Electrons in a soup of
protons (positive charges)
– There is an equal number
of positive and negative
charges because the atom
is neutral
Cathode Ray Tube Experiment
Thompson’s Model
Electrons
Protons
Ernest Rutherford
1910
• Nucleus Theory 1910
– alpha particle gold foil
experiment
• An atom’s mass is mostly
in the nucleus
• The nucleus has a
positive charge because
it contains the protons
and because it is so large
in mass it contains
another particle called the
neutrons(neutral)
• Electrons in fixed orbit
Alpha Particle Experiment
Rutherford Model
Niels Bohr
1913
• Planetary Model 1913
– Nucleus surrounded by
orbiting electrons at
different energy levels
– Electrons have definite
orbits
• Worked on the Manhattan
Project (US atomic bomb)
Bohr’s Model
Neutrons
(No charge)
Electrons
(negative
charge)
Protons (positive charge)
Ernst Schrödinger
Werner Heisenberg
• Quantum Mechanical
Model 1926
– Electrons are in probability
zones called “orbitals”, not
orbits and the location
cannot be pinpointed and
they are constantly moving
(they are not moving in
circular orbits)
– Schrödinger and
Heisenburg’s Model of the
Atom is the Model still
accepted today.
Schrödinger and Heisenburg’s
Model of the Atom
Atomic Theory
JJ
Thomson
Democratus
400 BC
1803
John
Dalton
1904
Niels
Bohr
1910
Ernest
Rutherford
1913
1926
Schroedinger
/ Heisenberg
Timeline Activity
• You are going to construct a timeline of
the development of the atom. It must
include:
– Dates (5 points)
– Scientists (5 points)
– A description of the discovery (20 points)
– A drawing of the atom (10 points)
– Appearance/Colorful (10 points)