-
400
Aristotle
-Democritus first discovered the existemce of a particle and called it "atomos"
-400 B.C
-proposed that all matter is made up of combinations of the 4 elements (air, earth, water and fire)
-Aristotle's atomic model differs from Democritus by having the 5 elements
-Aristotle's model has sections for each of the elements -
460
Democritus
-first person to discover the atom
-460 B.C
-proposed that all matter is made up of small particles that he called atoms
-first model, thought that it was a spherical marble shape
-marble shaped -
Antoine Lavoisier
-Isaac Newton
-1777
-proposed combustion, discovered the law of converting mass, discovered oxygen and hydrogen, and helped construct the metric system
-model is same as previous
-worked with Isaac Newton on discovering the law of the conversion of mass -
John Dalton
-Antoine Lavoisier
-1803
-Invented the atomic theory
-Dalton believed in Democritus' theory that the atom looked like a marble
-marble-shaped, spherical -
Henri Becquerel
-In 1895 Wilhelm Roentgen discovered that certain chemicals glow and set off penetrating rays that he called x-rays
-1896
-While studying the effect of x-rays on photographic film, he discovered some chemicals that were giving off those same penetrating rays which he later called identified as uranium which led to discovering radioactivity
-Becquerel's model has more details and information than Dalton's model
-Becqurel worked along side Marie & Pierre Curie
-has two nuclei -
J.J. Thomson
-Henri Becquerel
-1897
-discovered electrons
-got a spherical form, has layers
-has layers like an onion and electrons spread around the most outer layer -
Marie & Pierre Curie
-Ernest Rutherford
-1898
-discovered polonium and radium
-the model didn't change from Rutherford's time, the two elements just got added to the group of known elements at that time -
Max Plank
-Marie & Pierre Curie
-1900
-originated quantum theory
-didn't make a new model, just invented quantum theory -
Robert Millikan
-Hans Geiger
-1909
-discovered that electrons are negatively charged
-this model is more spherical than the last
-round and marble like with electrons spread around the surface -
Ernest Rutherford
-Robert Millikan
-1911
-Established that the nucleus is very dense, small and positvely charged, and that electrons are located outside the nucleus
-Rutherford's model has electrons around the outside of the nucleus
-has positive nucleus in center and negative electrons around the outside -
Henry Mosely
-Ernest Rutherford
-1914
-proposed that the atomic number of an element is equal to the number of protons in the nucleus which led him to discover that the periodic table is based upon the atomic number of an element instead of the atomic mass
-model is same as previous -
Niels Bohr
-Henry Mosely proposed that the atomic number of an element is equal to the number of protons in the nucleus and based the periodic table on atomic number instead of atomic mass
-1922
-discovered atomic structure
-Bohr's model has a more accurate amount of protons and electrons
-has a nucleus in the middle with protons in it and electrons on the rings in orbit around the nucleus
-Bohr studied under J. J. Thomson and Ernest Rutherford -
Werner Heisenburg
-de Broglie
-1927
-proposed Principle of Indeterminancy (you can not know both the position and velocity of a particle)
-model is same as previous -
Erwin Schrodinger
-Cockcroft/Walton
-1930
-combined the equations of behavior of waves with the de Broglie equation to generate a new and improved equation for the distribution of electrons in the atom
-previous model remained the same, Schrodinger's equation improved future models -
James Chadwick
-Erwin Schrodinger
-1932
-discovered existence of neutrons
-improved Bohr's model because of neutrons
--has a nucleus in the middle with protons and neutrons in it and electrons on the rings in orbit around the nucleus
-studied under Ernest Rutherford
