Transcript Development of Atomic Theory

Development of Atomic
Theory
In 440 BC, Democritus, a Greek
Philosopher theorized that if you cut
an object in half, then cut that one in
half, you would eventually end up with
a particle that could not be cut.
He called this an atom. From the Greek word
Atomos, meaning “not able to be divided.”
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In 1803 British chemist John Dalton published
his atomic theory.
All substances made of atoms, which are small,
cannot be created or divided or destroyed.
Atoms of same element are alike; different
elements made of different atoms.
Atoms join with different atoms to form new
substances.
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In 1897, the British scientist J.J. Thomson
discovered small particles inside of atom.
Negatively charged particles he called
corpuscles (electrons).
Cathode ray tube experiment.
Plum-pudding model: Positive particles mixed
with negative particles.
Development of Atomic Theory
J J Thomson: Cathode ray tube experiment
Development of Atomic Theory
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In 1909, Earnest Rutherford, a former student
of Thomson performed “gold foil experiment.”
http://www.mhhe.com/physsci/chemistry/esse
ntialchemistry/flash/ruther14.swf
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1911 published revised atomic theory.
Nucleus: tiny, dense, positively charged center of
atom where most of the mass is located.
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1913 Neils Bohr, Danish scientist, who worked
with Rutherford.
Electrons traveled in definite paths at specific
distances from the nucleus.
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Austrian physicist Erwin Schrödinger &
German physicist Werner Heisenberg
Electrons do not move in definite paths.
Electron paths cannot be predicted.
“Electron cloud” related to the paths described
in Bohr’s model.
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Parts of an atom
Nucleus
Proton
Neutron
Electron