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440 BCE
Democritus
Atoms are small, hard particles.
Atoms constantly move. -
440 BCE
Democritus
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Period: 440 BCE to
Atomic Theory
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John Dalton
All substances are made of atoms.
Atoms are "uncuttable."
Atoms of different elements are different.
Atoms of the same element are exactly alike.
Elements combine in specific proportions.
He conducted the cathode-ray tube experiment. -
John Dalton
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J.J. Thomson
He conducted the cathode-ray tube experiment.
His theory of the atomic structure lead to "plum-pudding" model.
There are small, negatively charged particles inside an atom. -
J.J. Thomson
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Ernest Rutherford
Atoms contain mostly empty space.
Electrons move in empty space in the atom.
He conducted the gold foil experiment.
Most of an atom's mass is in the nucleus.
There is a small, dense, positively charged nucleus. -
Ernest Rutherford
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Niels Bohr
Electrons jump between levels from path to path.
Electrons travel in definite paths. -
Niels Bohr
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Erwin Schrodinger and Werner Heisenberg
Electron paths cannot be predicted.
Electrons are found in electron clouds, not paths. -
Erwin Schrodinger and Werner Heisenberg
