Atomic Timeline

Democritus

8 BCE

Democritus was a Greek philosopher who discovered that there was a void between atoms and that atoms are different sizes

Crookes

Dec 1, 1879

carried out a minute investigation of thallium and its properties once he discovered it

Dalton

Dec 1, 1891

law of constant composition, law of multiple proportions, developed first useful atomic theory, 1st to associate atoms with stoichiometry

Becquerel

Dec 1, 1896

studied canal rays, discovered that atoms were associated with the proton H+

JJ Thomas

Dec 1, 1904

showed there were small charged particles called electrons, "developed the picture of an atom as a sphere of positive charge, occupying the whole volume of the atom, with electrons embedded in it.”

Rutherford

Dec 1, 1911

"Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm)gold foil .” and “Using x-ray tubes, determined the charges on the nuclei of most atoms.”, assumed electrons were outside the nucleus, discovered nucleus was small dense and positively charged

Bohr

Dec 1, 1913

Bohr proposed tha the hydrogen atom was one heavy proton with a lighter electron orbiting it, discovered that only certain orbits are permitted, electrons would not create radio waves, changing the orbit of an electron could change the color

Electron Cloud Model

Dec 1, 1926

”Schrödinger and Werner Heisenburg (1901-1976) mathematically determined regions in which electrons would be most likely found"

Chadwick

Dec 1, 1932

used alpha particles to discovered a neutron atomic particle with a mass close to the proton, discovered neutron

currently used

Dec 1, 2016

The currently used atomic model is the electron cloud model however the Bohr model may be used when it is convenient