J.W.

Democritus

300

(460 BC-370 BC) Called particles of matter atoms.

John Dalton

Jan 1, 1803

John Dalton (1766 - 1844) developed the first useful atomic theory of matter. Dalton developed the hypothesis that the sizes of the particles making up different gases must be different then the particles found in liquids. His theory included that atoms were spherical solid masses in motion.

JJ Thomson

Jan 1, 1897

Joseph John Thomson (1856–1940) discovered the electron using a cathode-ray tube

Neils Bohr

Jan 1, 1903

Niels Bohr (1871-1937) applies his theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits, creating the "Bohr Planetary Model".

Ernest Rutherford

Jan 1, 1911

Ernest Rutherford's atomic theory described the atom as having a central positive nucleus surrounded by negative orbiting electrons. (atom is mostly empty space). He discovered the proton in his "gold foil" experiment.

Quantum Mechanics

Jan 1, 1913

Niels Bohr's discovery of electrons lead to the study of Quantum Mechanics.

Erwin Schrodinger

Jan 1, 1926

Erwin Schrodinger's most important contribution to the modern atomic theory was his development of the mathematical description that described the paths electrons would most likely follow in their orbits around nucleus. (electron cloud)

James Chadwick

Jan 1, 1932

James Chadwick (1891-1974) discovered a particle within the nuecleus that has mass simular to that of a proton, therefore the neutron was said to be found in 1932.

Cockroft and Walton

Jan 1, 1932

Found out how to split the atom.

Fission

Jan 1, 1932

The study of fission or spliting the atom came from the discovery of the neutron by Chadwick.

Atomic Bomb

Jan 1, 1945

After Cockroft and Walton found out how to split the atom it led to the atomic bomb. The atomic bomb was also used to end WWII after it was dropped on Hiroshima.