History of the Atom

Democritus

Jan 1, 1000

Democritius discoadeverd matter is made of small indiviual paricles which have different forms postions and arrangements, which he named atoms.

John Dalton

Jan 1, 1803

Dalton developed the atom theory, stating that spherial atom have measured propertied of mass. He also develped the concept of moles.

Goldstein

Jan 1, 1886

Goldstein discoverd canal rays which are postively charged equal to an atom.

J.J Thompson

Jan 1, 1897

Thompson discoverd the negatively charged electron in the cathode ray tube. He datermined that the electron was a component of all matter and calculated the charge to mass ratio for the electron. It is e/m= 1.76 x 10^8 coulombs/grams. He also discover protons are too associated with canal rays.

Robert Millikan

Jan 1, 1909

Millikan determined the unit charge of an electron by performing an oil-drop experiment. The formula is e+ 1.60 x 10^-19 coulombs.

Ernest Rutherford

Jan 1, 1911

Rutherford found that an atom has a small, dense, postively charged nucleus, and that the electrons move around the nucleus.

Neils Bohr

Jan 1, 1913

Bohr discovered how electrons move in a circular orbit at a fixed distance from the nucleus.

Erwin Schrodinger

Jan 1, 1926

Schrodinger developed a mathematical equation to describe the motion of electrons in atoms. His work leads to the electron cloud model.

James Chadwick

Jan 1, 1932

Chadwick confirmed the extistance of neutrons which have no charge Atomic nucluei contain neutrons and postively chraged protons.