Models of Atoms
atom
The Electron
JJ Thomson used the
cathode ray tube to
prove that the atom
was made up of
electrons
Click here to listen
to him talk about it
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But, what was that green light?
Was it a light?
Was it a particle?
To test this, he brought a magnet close to
the cathode ray tube to see what would
happen.
• So, the magnet caused the cathode ray to
move. What does that tell us?
• Would a magnet affect a light from a
flashlight? (you could try this at home)
• Probably not.
• Therefore, the cathode ray must be a
particle!
1897 - J.J. Thompson
• Negatively charged
electrons stuck into a
lump of positively
charged material.
• Explained some
electrical properties
• It did not explain
number of protons
and electrons.
Plum-Pudding model
Plum Pudding is an English dish sort of like bread
pudding with raisins in it.
An American analogy to his atom
would be…
…Is like…
But we’ll still refer to it as the “Plum Pudding” model in class
Bohr’s Model
• “Planetary Model”
• Electrons are
arranged in circular
paths or orbits,
around the nucleus.
• Electrons move have
fixed energy so they
don’t fall into the
nucleus.
Ernest Rutherford
In 1908, Rutherford performed the Gold
Foil Experiment. Proposed a nuclear
atom in which electrons surround a
dense nucleus. Thought of the rest of
the atom as mostly empty space.
(1871-1937)
In the experiment, he shot
alpha particles (very small,
very dense, very fast
particles) at a thin layer of
gold foil.
• He expected all of the alpha particles to go
straight through
• It would be like if you were shooting bullets
at a cake…all of the bullets (or alpha
particles) would go straight through the
cake (or gold foil atoms)
Gold foil
Detector
screen
Alpha
particles
source
Alpha
particles
Thomson’s
Atom
Alpha
particles
Or…
Quantum Mechanical Model
• Erwin Schrodinger used a
mathematical approach to
describe an atom.
• It estimates the probability
of finding an electron. The
fuzzy cloud represents an
area that there is 90%
probability of finding an
electron.