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400 BCE
Democritus
Born around 460 BCE. Died around 370 BCE. Thought that atoms are tiny, uncuttable, solid objects that move around at random. Broke a seashell in half until he had a fine powder, and took the smallest piece of the powder and tried to break it and failed. Democritus also worked on the void hypothesis, made popular by Parmenides. Developed Democitus's model. -
John Dalton
Born on September 6, 1766. Died on July 27, 1844. He discovered that all matter was composed of atoms, invisible and indestructible building blocks. He experimented with gases to make this discovery. Dalton started working as a teacher at the age of 12. The first part of Dalton's theory states that all matter is made up of indivisible atoms. The second part of his theory states that all atoms of a given element are identical in mass and properties. -
JJ Thomson
Born on December 18, 1856. Died on August 30, 1940. He discovered the electron. Experimented with a Crookes, or cathode ray, tube, which proved that cathode rays are negatively charged, proving the existence of the electron. Thomson won a Nobel Prize for physics in 1906 because of his work with the atom. Thomson developed the plum pudding model of the atom -
Robert Millikan
Born- 03/22/1868
Died- 12/19/1953
Lived in Maquoketa, Iowa
Discovered the value of electrons
Experiment-oil drop experiment; charged drops of oil balanced between two plates
Interesting fact- Millikan was the first to receive a P.h.D from the physics department at Colombia University
No particular change to the atomic model -
Robert Millikan
Born on March 22, 1868. Died on December 19, 1953. Lived in Maquoketa, Iowa. He discovered the value of electrons. He performed the oil drop experiment where charged oil drops are put into the electric field and were balanced between two plates. Millikan was the first to receive a Ph. D from the physics department at Colombia University. His discovery did not change the atomic model at the time. -
Ernest Rutherford
Born- 08/30/1871
Died- 10/19/1937
Lived in Montreal, Canada
Discovered that atoms have a nucleus that is circled by electrons
Experiment- gold foil experiment: shot minute particles through a thin layer of gold foil
Interesting fact- He was the first person from Oceania to win a Nobel Prize
Developed the Rutherford Model or planetary model -
Ernest Rutherford
Born on August 30, 1871. Died on October 19, 1937. He lived in Montreal, Canada. Discovered that atoms have a positively charged nucleus surrounded by empty space and electrons. Used the gold foil experiment, which is an experiment where alpha particles are shot at a thin layer of gold foil. Ernest Rutherford was the first person from Oceania to win a Nobel Prize. He developed the Rutherford model, or the planetary model. -
Neils Bohr
Born on October 7, 1885. Died on November 18, 1962. Bohr discovered that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element. Bohr propsed a theory based on quantum theory that energy is transferred only in certain quantities. A fun fact about Bohr is that he set off an explosion in his university laboratory. He develped the Bohr model. -
Erwin Schrodinger
Born on August 12, 1887. Died on January 4, 1961. He discovered new, productive forms of the atomic theory. He developed a number of fundamental results in the field of quantum theory. He is still referred to as the father of quantum physics. Schrodinger did not make any particular changes to the atomic model. -
James Chadwick
Born on October 20, 1891. Died on July 24, 1974. Chadwick discovered the neutron. He put a piece of beryllium in a vacuum chamber with some polonium. The polonium emitted alpha rays, which struck the beryllium. When struck, the beryllium emitted neutral rays. He received the Hughes Medal of the Royal Society in 1932. He did not change the atomic model.
