History of the Atom

Particle Theory 400 bc

400

Greek philosiphers such as Democritus develope a theory that says that everything is made out of a basic partice that can't be divided, the atom.

Atomic Theory

Oct 21, 1808

John Dalton proposed an atomic theory that relates with the law of conservation of mass. Basically it says that all mass is made of atoms and can't be destroyed, only converted.

Discovery of Electrons

Oct 20, 1897

J J Thompson discovers the electron while working with cathode rays. This proves wrong the theory that atoms are the smallest paricles and creates the plum pudding model, which says that negatively charged electrons (plums) are floating in a positively charged field (pudding).

Measuring Electrons

Oct 21, 1909

Robert Millikan, an american scientist measured the charge of electrons, giving scientists a somewhat accurate measurement of its mass.

Discovery of the Nucleus

Oct 20, 1911

The nucleus of an atom is discovered by Ernest Rutherford. Up until this point in time, scientists had never had a correct idea of what atoms look like.

Atomic Structure

Oct 21, 1913

Niehls Bohr creates a successful theory of atomic structure based on current (for then) quantum ideas.

Nuclear Force

Oct 21, 1921

James Chadwick and E S Biehler agree with each other that some unknown, strong force holds atoms together.

Atomic Conservation

Apr 19, 1925

Hans Gieger alon with Walther Bothe demonstrates that both mass and energy of atoms are conserved in atomic processes.

Fundamental Particles

Oct 20, 1930

It is established by Paul Dirac and Max Born that there are three fundamental parts in quantum physics: protons, electrons and photons.

Neutrons

Oct 21, 1931

James Chadwick discovers a particle that lacks a charge, the neutron.

Nucleon

Oct 21, 1941

C. Moller and Abraham Pais propose the term nucleon for associated use with the group of protons and neutrons in the center of an atom.