The History of Atomic Models
Sandy S. Bryan
Wagener-Salley High School
This lesson is for Mrs. Bryan's ninth grade physical science classes.
This lesson, The History of Atomic Models, corresponds to chapter
five section one from our text book. Specifically, this lesson is
about five scientists and their contributions to the atomic model, as well
as the currently accepted wave model. The scientists we will study
include Democritus, John Dalton, J.J. Thompson, Ernest Rutherford, and
Neils Bohr. The important concept here is that no one scientist created
the entire "picture" of the atomic model. Instead, each person added
a "piece" to the model, or puzzle if you will, using the scientific method.
Remember, the model is still in progress. You may be the next scientist
who adds another "piece" to the atomic model "puzzle." The scientific
method is a never-ending cycle.
Proposed that all objects had a smallest piece.
He named his smallest piece the atom.
John Dalton 1803
Atoms are indivisible. (This is what Democritus said!!)
Atoms are indestructible.
Atoms of the same kind are called elements.
Atoms of different kinds are called compounds.
J.J. Thomson 1897
Called his theory the Plum Pudding or Raisin Bun model.
Discovered the electron, which is the raisin in the bun of positive charges.
Ernest Rutherford 1908
Used a gold foil experiment.
Said that there is a center of an atom, or nucleus, that contains positive
Neils Bohr 1913
Said that the electrons go around the nucleus in orbitals or energy levels.
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This is the model accepted today.
We can not determine the exact location of an electron, but we can determine
a probable or likely location of an electron.
States that there are two electrons in the first energy level, or orbital,
closest to the nucleus.
There are eight electrons in the second energy level.
There are eight electrons in the third energy level.
There are sixteen electrons in the fourth energy level.
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