History Of the Atom

Aristotle(384-322BC)

322

he believed in the four elements of air, earth, fire, and water. He felt that regardless of the number of times you cut a form of matter in half, you would always have a smaller piece of that atom.

John Dalton

Dec 12, 1803

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

Henri Becquerel

Dec 12, 1896

He discovered that some chemicals spontaneously decompose and give off very pentrating rays while he was studying the effect of x rays.

JJ Thomson

Dec 12, 1897

he identified the negatively charged electron in the cathode ray tube in 1897. He deduced that the electron was a component of all matter and calculated the charge to mass ratio for the electron.Thomson proposed the "plum pudding" model of the atom.

Marie and Perrie

Dec 12, 1898

She Studied uranium and thorium and called their spontaneous decay process "radioactivity". She and her husband Pierre also discovered the radioactive elements polonium and radium.

Max Planck

Dec 12, 1900

used the idea of quanta (discrete units of energy) to explain hot glowing matter.

Robert Millikan

Dec 12, 1909

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.

Ernest Rutherford

Dec 12, 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.

Henry Mosely

Dec 12, 1914

Using x-ray tubes, her 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

Dec 12, 1922

His atomic model had atoms built up of succesive orbital shells of electrons. He developed an explanation of atomic structure that underlies regularities of the periodic table.

Werner Heisenberg(1927)

Dec 12, 1927

He Proposed Principle of Indeterminancy - you can not know both the position and velocity of a particle.

James Chadwick

Dec 12, 1932

James Chadwick discovered the neutron in 1932. Chadwick was a collaborator of Rutherford's. The discovery of the neutron led to the discovery of fission and ultimately to the atomic bomb

Democritus(Greek era)

Dec 12, 2013

First proposed the existence of an ultimate particle. Used the word "atoms" to describe this particle.

Antoine Lavoiser(late 18th century)

Dec 13, 2013

Antoine Lavoisier formulated the theory of conservation of mass. This showed that matter (atoms) couldn’t be created or destroyed, which supported the theory of Democritus.

Erwin Schrodinger

Dec 13, 2013