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By: Emily Landers & Alex Strickland
Aristotelian Atomic Theory
Ancient Greeks believed that there were
only four elements that everything was
made up of:
More of Aristotle…
All earthly substances originate from these four
elements. When comparing a tree to a rock,
different amounts of the four elementals exist
in each to create the differences we see or
The elements were “pure” but could not be
found in the state on earth. Every visible thing
was made up of combinations of earth, water,
air, and fire.
&& some more
While we do know now that theses
previous theories are false, in a way the
four elements do align with the four
states of matter that modern science has
agreed on: solid (earth), liquid (water),
gas (air), and plasma (fire).
Cathode Ray Experiment
Cathode-ray tubes supplied evidence of the
existence of electrons, which are
negatively charged subatomic particles
that have relatively little mass.
This then lead to the Plum Pudding Model…
Plum Pudding Model
In J.J. Thomson’s Plum Pudding Model each atom was a
sphere filled with a positively charged fluid. The fluid was
called “pudding”. Scattered in this fluid were electrons
known as the “plums”.
Plum Pudding continued
The plums pudding model was proposed in 1904 before the
discovery of the atomic nucleus.
It has also been called the 'chocolate chip cookie model or
"Blueberry Muffin Model"
Dalton’s Solid Sphere Model
Also known as the Billiard Ball Model
He described atoms as indivisible spheres
with constant density throughout. Dalton
also said that all atoms of the same element
were identical and different from those
atoms composing another element.
This was not accurate. J.J. Thomson conducted a new
That didn’t prove it wrong, but added on information to it.
Rutherford’s Nucleus Model
 Rutherford took a piece of gold foil. The gold foil was
secured so that particles from a radioactive source
(Polonium) could be directed at the gold foil. A
fluorescent screen was used to detect where the
radioactive particles ended up.
Most of the alpha particle went right through the gold foil unaffected. A
few were deflected and even fewer were reflected off the gold foil.
These astounding discoveries led to Rutherford's Model of the atom:
Atoms are not solid masses.
Most of the atom is made up of space as indicated by the fact that
most of the radioactive particles went right through the foil unaffected.
The atom has a central, small, solid, and positively charged part that
Rutherford called the nucleus.
Gold Foil Experiment
If J.J. Thomson’s theory was correct then the alpha
particles should have gone straight through the atom, but
as shown in the model below…that did not happen.
The Atomic Model
Bohr solar system model
This model was proposed by Niels Bohr in 1915 .
In the Bohr Model the neutrons and protons
(symbolized by red and blue balls in the adjacent
image) occupy a dense central region called the
nucleus, and the electrons orbit the nucleus much
like planets orbiting the Sun.
Electron Cloud
Electron Cloud Model (1920's)- an atom consists of a dense
nucleus composed of protons and neutrons surrounded by
electrons that exist in different clouds at the various energy
levels. Erwin Schrodinger and Werner Heisenburg
developed probability functions to determine the regions or
clouds in which electrons would most likely be found.