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440 BCE
Democritus
Atoms are "uncuttable".
All substances are made of atoms.
Atoms are small, hard particles.
Atoms constantly move. -
440 BCE
Democritus
Atomic Model -
Period: 440 BCE to
Atomic Theory Timeline
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John Dalton
Atoms of different elements are different.
Atoms of the same element are exactly alike.
Elements combine in specific proportions.
He conducted experiment in combining elements. -
John Dalton
Atomic Model -
J.J. Thomson
He conducted the cathode-ray tube experiment.
His theory of the atomic structure lead to the "Plum-Pudding" model.
There are small, negatively charged particles inside an atom. -
J.J Thomson
Atomic Model -
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
Atomic Model -
Niels Bohr
Elements jump between levels from path to path.
Electrons travel in definite paths. -
Niels Bohr
Atomic Model -
Erwin Schrodinger and Werner Heisenberg
Electrons are found in electron clouds, not paths.
Electron paths cannot be predicted. -
Erwin Schrodinger and Werner Heisenberg
Atomic Model
