Atomic Structure

Dalton

Oct 16, 1803

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

JJ. Thompson

Oct 16, 1897

Used a CRT to experimentally determine the charge to mass ratio (e/m) of an electron =1.759 x 10 8 coulombs/gram.
Studied "canal rays" and found they were associated with the proton H +

Rutherford

Oct 16, 1911

Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0.00006 cm) gold foil . He established that the nucleus was: very dense,very small and positively charged. He also assumed that the electrons were located outside the nucleus.

Bhor

Oct 16, 1922

Developed an explanation of atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up of sucessive orbital shells of electrons.

Chadwick

Oct 16, 1932

Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron.

The Modern Model

Oct 16, 2012

Electrons are in constant motion around the nucleus, protons and neutrons jiggle within the nucleus, and quarks jiggle within the protons and neutrons.