History of the Atom Timeline by (Mercedes Harris)

Democritus

400

Found the atom.
All atoms are invisible
http://www.universetoday.com/60058/democritus-atom/

Aristotle

450

Discovered Matter
Defining the subject of matter
http://scienceblogs.com/dotphysics/2009/09/04/the-development-of-the-atomic-model/

Dalton

Mar 5, 1803

Proposed the atomic theory with the microscope method.
All matter is made of atoms.
Atoms are indivisible and indestructible.
http://scienceblogs.com/dotphysics/2009/09/04/the-development-of-the-atomic-model/

Thomson

Mar 5, 1897

Discovered electrons called "Plum Pudding" model
Used the method of designing to study the nature of electric discharge in a high- vaccum cathode- ray tude
http://scienceblogs.com/dotphysics/2009/09/04/the-development-of-the-atomic-model/

Bohr

Mar 5, 1922

Niel's Bohr discovered the Bohr model which proves that the atom has small positively charged nucleus.
http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html

Heisenberg

Mar 5, 1925

Werner Heisenberg discovered allotropic forms of hydrogen and developed a theory of quantum physics.
Discovered Electron Cloud Theory
http://scienceblogs.com/dotphysics/2009/09/04/the-development-of-the-atomic-model/

Rutherford

Mar 5, 1926

He developed "The Gold Foil Experiment" and determined the nucleus of an atom is dense.
http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html

Schrodinger

Mar 5, 1926

Erwin Schrodinger proposed the modern atomic model, known as the "Wave- Mechanical" model.
Both Schrodinger and Heisenberg discovered the Electron Cloud Theory