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440 BCE
Democritus
Atoms are "uncuttable"
Atoms are small, hard particles
Atoms constantly move -
440 BCE
Democritus
Atomic Model -
Period: 440 BCE to
Atomic Theory
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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 alike
Elements combine in specific proportions
He conducted experiments in combining elements -
John Dalton
Atomic Model -
J.J. Thomas
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
Electrons travel in definite paths
Electrons jump between levels from path to path -
Niels Bohr
Atomic Model -
Erwin Schrodinger and Werner Heisenberg
Electron paths cannot be predicted
Electrons are found in electron clouds, not paths -
Erwin schrodinger and Werner Heisenberg
Atomic Model
