Atomic Timeline

Democritus Model

460 BCE

Experiment- Theory
Discovery- All matter consists of invisible particles called atoms

John Dalton

Nov 30, 1803

Experiment- Mixtures of gases to determine the effect the individual gases had on a whole
Discovery- Developed first useful atomic theory

Crookes Model

Nov 30, 1879

Experiment- Studied the effects of sending an electric current through a gas in a sealed tube
Discovery- Cathodes; electrodes at either end and electrically charged particles

Becquerel Model

Nov 30, 1896

Experiment- Studying fluorescent properties in uranium salts, placed uranium salts on top of a photographic plate wrapped in black paper
Discovery- Radioactivity

Thomson model

Dec 1, 1897

Experiment- Developed the picture of an atom as a sphere of positive charge, occupying the whole volume of the atom, with electrons embedded in it
Discovery- Able to explain some chemical properties of the many kinds of atoms known at this time

Rutherford

Dec 1, 1911

Experiment- Developed a solar system-like model of an atom
Discovery- Positive charge of the atom was concentrated in a very small volume

Niels Bohr

Dec 1, 1922

Experiment- Creating the model of an atom
Discovery- That electrons move in circular orbits around the atomic nucleus.
(currently used to represent the atom)

Electron Cloud model

Dec 1, 1926

Experiment- Developed an equation to calculate chances of electron being in any given place
Discovery- Orbitals
(accepted model)

Chadwick Model

Dec 1, 1932

Experiment- Beryllium atoms with alpha particles
Discovery- Neutron