History of the Atom

Democritus

450

Experiment- cut an apple into many different smaller pieces to determine there was a point where matter could no longer be cut into smaller pieces
Dicovered- "atomos" , introduced the idea of the atom

John Dalton

Sep 14, 1800

Experiment- studied the pressure of gases, the properties of compounds, performed a series of different experiments on a mixture of gases
Discovery- atoms do exist, gases must consist of tiny particles in constant motion, a compound always consists of he same elements in the same ratio, theory of the atom, Daltons Atomic Theory

J.J. Thomson

Sep 14, 1897

Experiment- vacuum tube experiment, he was interested in electricity, he passed an electric current through a vacuum tube, Thomsons plum pudding model, shows the atom as a sphere of positive charge with negative electrons scattered through it
Discovery- electrons, first subatomic particles to be identified,

Ernest Rutherford

Sep 14, 1911

Experiment- used alpha particles to study atoms, he aimed a beam at a very thin sheet of gold foil, outside the foil he placed a screen of material that flowed when alpha particles struck it,
Discovery- the nucleus, all positive charge of an atom is concentrated in a small area (nucleus) , later discovered it contains positively charged particles (protons)
Also predicted the existence of neutrons.

Bohr

Sep 14, 1913

Experiment- passed onto a study of the structure of the atom,
Discovery- worked out and presented a picture of the atomic structure, which still serves as clarification on the physical and chemical properties, (has been improved)