-
Democritus' Theory
Democritus proposed that there was a limit to how much matter could be subdivided and that there existed an ultimate, indivisible particle called an atom. No experiments were done at this stage. -
Newtown's Theory
Isaac Newton proposed a mechanical universe with small solid masses in motion. He also produced the three laws of motion. -
Dalton's discovery
Dalton did many experiments and found that elements always combined in fixed ratios. He also proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
G.J Stoney's Theory
G.J. Stoney proposed that electricity was made of discrete negative particles he called electrons. -
J.J. Thomson's experiments
Thomson and other scientists all experimented with passing electricity through gases at low pressures in sealed glass tubes, -
Plank's explanation
Max Planck used the idea of quanta (discrete units of energy) to explain hot glowing matter. -
Nagaoka's theory
Nagaoka postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. -
Milikan's experiment
Milikan's oil drop experiment determined the charge and mass of an electron. -
E. Rutherford's Theory
He established that the nucleus was: very dense, very small and positively charged. He also assumed that the electrons were located outside the nucleus. -
H.G.J Mosely's theory
He wrote “The atomic number of an element is equal to the number of protons in the nucleus". -
James Chadwick's experiment
The neutron was discovered. -
Bohr's discovery
Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of successive orbital shells of electrons.