History of the Atom

Democritus

442

Greek philosopher, who developed the atomic theory of the universe,His atomic theory anticipated the modern principles of the conservation of energy and the irreducibility of matter.

John Dalton

Oct 29, 1803

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

E. Goldstein

Oct 31, 1886

Used a CRT to study "canal rays" which had electrical and magnetic properties opposite of an electron. 1895 Wilhelm Roentgen

J.J Thompson

Oct 29, 1897

Heused a CRT to experimentally determine the charge to mass ratio (e/m) of an electron=1.759*108 colombus/gram studied "canal rays" and the found they were associated with the Proton Ht.

Robert Millikan

Oct 31, 1909

American physicist, best known for his work in atomic physics and major science, dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces.

Ernest Rutherford

Oct 31, 1911

British physicist, who became a Nobel laureate for his pioneering work in nuclear physics and for his theory of the structure of the atom. 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.

Neils Bohr

Oct 31, 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.

Erwin Schrodinger

Oct 31, 1930

Viewed electrons as continuous clouds and introduced "wave mechanics" as a mathematical model of the atom.

James Chadwick

Oct 31, 1932

Using alpha particles discovered a neutral atomic particle with a mass close to a proton. Thus was discovered the neutron. British physicist James Chadwick measured the energy of the protons emerging from the hydrogen atoms.