Atomic Theory

Aristotle

350

*Disagreed with Democritus's model of the atom.
*Felt that there was no smallest part of matter and that different substances were made of earth, fire, air, and water

Democritus of Adbera

400

First person discover that all matter is made up of invisible particles called atoms.
Created the name "atom"

John Dalton

Jan 1, 1803

Created the Atomic Theory of Matter
Believed atoms of different elements combine in whole ratios to form chemical compunds

Joseph John Thomson

Jan 1, 1897

Discovered the electron Created the "Plum Pudding" atomic model

Max Planck

Jan 1, 1900

Created the Quantum Theory which led to the understanding of energy levels in atoms

Robert Millikan

Jan 1, 1908

Proved J.J. Thompson hypothesis that the electron is 1000x smaller than the atom

Ernest Rutherford

Jan 1, 1909

Created the nucleus Believed that only the Nucleus was positive

Niels Bohr

Jan 1, 1913

Created energy levels in the atom, where only a certain amount of electrons could fit on one energy level of a atom

Erwin Schrodinger

Jan 1, 1926

Believed that the only way to find the location and energy of an electron in an atom was to calculate its probability of being a certain distance from the nucleus.

Werner Heisenberg

Jan 1, 1927

Believed that you can't know the exact velocity and momentum of the electron at the same time, which means you can't know the exact location of the electron

Lous deBroglie

Aug 19, 1929

discovered of wave nature of electrons

James Chadwick

Jan 1, 1932

Discovered the neutron Believed that the atom was neutral because the negative electrons and the positive protons cancelled out