History of an atom

Democritus

Oct 29, 1000

Proposed that everything id msde up of small particles and called them "Atoms".
"By convention bitter, by cinvention sweet, but in reality atoms and void."

John Dalton

Oct 29, 1803

Proposed an "atomic theory" with spherical solid atoms based upon measurable properties of mass.

Eugen Goldstein

Oct 29, 1886

Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron

J.J Thomson

Oct 29, 1897

Used a CRT to experiment determine the charge to mass ratio (e/m) of an electron=1.759*10^8 columbs/gram. Studied "canal rays"
Model called "plum pudding"

Ernest Rutherford

Oct 29, 1909

Proposed that the atom has a central positive nucleus surrounded by negative orbiting electrons, that most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space that has enough positive charge to account for the great deflection of some of the alpha particles

Niels Bohr

Oct 29, 1915

Proposed that electrons travel in specific circular paths, or orbit, orbits around the nucleus defined by their angular momentum

Robert Millikan

Oct 29, 1917

From 1908-1917 He carried out experiments (oil-drop experiment) to find the quantity of charge carried by an electron. Using that value and the charge-to-mass ratio (Thomson), he calculated the mass of the eletron.
Mass= 1/1840 the mass of a hydrogen atom.

James Chadwick

Oct 29, 1932

Confirmed the existence of neutrons which have no charge. Atomic nulei contain neutrons and positively charged protons

Erwin Schrodinger

Oct 29, 1933

Developed mathematical equations to describe the motion of electrons in atoms. Also, he stated that electrons behave in a wave-like manner rather than just as particles and that their exact location within an orbit could not be precisely calculated.