-
Jun 29, 1450
Democritus
(450 B.C) Created 1st atomic theory: proposed that all matter is made up of particles called atoms, meaning indivisible. -
Issac Newton
Used small solid masses in motion to propose a mechanical universe -
John Dalton
Created 1st useful Atomic theory: Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass. -
G. J. Stoney
Proposed that electricity was made of discrete negative particles he called electrons -
J. J. Thomson
Discovered the first electron. Determined the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.
found ‘canal rays’ were associated with the proton H + . -
Max Planck
Inventor of Quantum theory: explained hot glowing matter. -
Nagaoka
Postulated a "Saturnian" model of the atom with flat rings of electrons revolving around a positively charged particle. -
R. A. Millikan
Oil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and the mass (m = 9.11 x 10 -28 gram) of an electron. -
Sir Ernest Rutherford
Father of nuclear physics: discovered that the atom's nucleus is very small in relation to the entire atom. He proposed that the negatively charged electrons were revolving around a heavier, charged nucleus. -
H. G. J. Mosely
Determined the charges on the nuclei of most atoms. He wrote "The atomic number of an element is equal to the number of protons in the nucleus". This work was used to reorganize the periodic table based upon atomic number instead of atomic mass. -
Niels Bohr
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. -
James Chadwick
Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.
