-
400 BCE
Democritus
Father of modern atomic theory; five parts of his atomic theory including that elements are composed of atoms and that element’s atoms are identical in mass. -
300 BCE
Aristotle
Dismissed Democritus’ atom as “worthless.” Said that the four elements were earth, fire, air and water. -
John Dalton
He was the first person to identify the possibility of an atom. -
John Dalton's Indivisible, Solid Sphere Model
-
J.J. Thomson
Discovered the electron. -
J.J. Thomson's Plum Pudding Model
-
R.A. Millikan
Determined the charge and mass of an electron through the oil drop experiment. -
Ernest Rutherford
Said that an atom has a small positive nucleus and the remainder is empty space through the gold foil experiment. -
Ernest Rutherford's Nuclear Model
-
Niels Bohr
Predicted that electrons travel in specified energy levels. -
Niels Bohr's Planetary Model
-
Henry Moesley
He stated that the atomic number of an element is equal to the number of protons in the nucleus. -
Louis de Broglie
Worked with Einstein to determine that electrons were similar to particles and waves. -
Werner Heisenberg
Came up with the “uncertainty principle”, which stated that it is impossible to determine the position and momentum of a particle at the same time. -
Erwin Schrodinger
Viewed electrons as a cloud and introduced wave mechanics as a model for the atom. -
Erwin Schrodinger's Quantum Mechanical Model
-
James Chadwick
Discovered the neutron.
