History of the Atom


Democritus’s Atomic Philosophy

460 BC - 370 BC

Born in Abdera, Greece 460 BC
Died in 370 BC
All matter consists of invisible particles called atoms
Atoms are indestructible
Atoms are solid but invisible
Atoms are homogenous
Atoms differ in size shape, mass, position, and arrangement
Solids are made of small, pointy atoms
Liquids are made of large, round atoms
Oils are made of very fine, small atoms that can easily slide past each other

Dalton’s Atomic theory

1766 - 1844

Elements are made of extremely small particles called atoms.
Atoms of a given element are identical in size, mass, and other properties; atoms of different elements differ in size, mass, and other properties.
Atoms cannot be subdivided, created, or destroyed.
Atoms of different elements combine in simple whole-number ratios to form chemical compounds.

Eugen Goldstein

September 5, 1850 - December 25, 1930

September 5, 1850 in Gleiwitz, Prussia
December 25, 1930 in Berlin, Germany
He discovered canal rays, the positively-charged particles formed when electrons are removed from the gas particles in a cathode-ray tube
Goldstein’s work suggested the presence of the proton

J.J. Thomas

December 18, 1856 - August 30, 1940

Joseph John Thomas
Cheetham Hill, a suburb of Manchester on December 18, 1856
In Cambridge on August 30, 1940
Owens College, Manchester
Trinity College, Cambridge as a minor scholar
Discovered that all matter is made up of tiny particles that are much smaller than atoms
Originally called ‘corpuscles’
Now called electrons
Proved the existence of isotopes

Max Planck

April 23, 1858 - October 4, 1947

April 23, 1858, Kiel, Germany
October 4, 1947, Göttingen, Germany
Contributions to the Atom
Discovered that hot objects do not radiate continuous ranges of energy
Heated objects radiate specific energy values
Started the development of “The Quantum Theory”

Marie Curie

November 7, 1867 - July 4, 1934

In Warsaw on November 7, 1867
In Savoy, France on July 4, 1934
Contributions to Atom Structure
Discovered and coined the word radioactivity
Discovered radioactive elements polonium and radium
With polonium and radium her and her husband further developed xrays

Robert A. Milikan

March 22, 1868 - December 19, 1953

Robert Andrews Millikan
March 22, 1868
Morrison. IL
December 19, 1953
San Marino, California
Contributions to Atom structure
Proved the electrical charge.
Created the famous ‘Oil drop experiment’
Dropped small electronically charged drops of oil suspended between two metal plates. They were then subjected to gravity and the attraction of an electrical field. He measured how the drops of oil moved around and then proved the electrical charge.

Ernest Rutherford

August 30, 1871 - October 19, 1937

August 30, 1871 in Spring Grove, New Zealand
October 19, 1937 in Cambridge, Cambridgeshire
Contributions to the Atom
Rutherford was the central figure in the study of radioactivity, and with his concept of the nuclear atom he led the exploration of nuclear physics.

Niels Bohr

October 7, 1885 - November 18, 1962

October 7, 1885 in Copenhagen Denmark
November 18, 1962 in Copenhagen Denmark
Contribution to the Atom
He was the first to apply the quantum concept, which restricts the energy of a system to certain discrete values, to the problem of atomic and molecular structure

Erwin Schrodinger

August 12, 1887 - January 4, 1961

August 12, 1887 in Vienna, Austria
January 4, 1961 in Vienna, Austria
Contribution to the Atom
Developed a powerful model of the atom
He combined equations for the behavior of waves with the De Broglie equation to generate a mathematical model for the distribution of electrons in an atom

James Chadwick

Oct 20, 1891 - July 24,1974

Sir James Chadwick
Oct 20, 1891
July 24,1974
Contributions to Atom structure
James discovered the particle in the nucleus of an atom that is the neutron because it has no electrical charge.
He led the British team in the Manhattan Project, in which the UK and Canada supported the USA’s World War 2 effort to build the world’s first nuclear bomb.

Louis De Broglie

August 15, 1892 - March 19, 1987

August 15, 1892, Dieppe, France
March 19, 1987, Louveciennes, France
Contributions to the Atom
Performed further research on the Quantum Theory
Discovered the wave movement of electrons

Werner Heisenberg

December 5, 1901 - February 1, 1976

December 5, 1901, Würzburg, Germany
February 1, 1976, Munich, Germany
Contributions to the Atom
He invented matrix mechanics which was the first formalization of quantum mechanics
Determined the speed and location of a particle has errors and are not constant
Developed the uncertainty principle - behavior of particles can only be determined through probability and are not constant or consistent in nature