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