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450
Aristotle
Ancient greek theorist from 450 B.C stated that all substances were made of earth, fire, wind, and water. He said that that matter is continuous and not made of smaller paticles. He did not have any evidence that the atom was accurate. -
450
Democritus
Democritus was an anceint greek theorist from 450 B.C. He came up with the notion of atoms. He said the world consists of a piece of matter that is the smallest part of "Atoms" and empt space. The atom was adopted because chemists provided a basis for this idea by showing that certain substances could not be further broken down by chemical methods. -
Period: 500 to
Atomic Theory Timeline
From 500 B.C till present. -
John Dalton
John Dalton was an englsh theorist from the 1780's and was consdered the "Father of Atomic Theory". He first stated that atoms make up elements, then atoms of the same element are identical, atoms of different elements are different. Then he said atoms of different elements react to form compounds and that atoms cannot be created of destroyed, only changed. -
J.J Thompson
J.J Thompson is a British theorist that discovered electrons and isotopes. He invented the mass specrtomere. He used the Plum Pudding Model to discover the electron and said that they move like planets around the nucleus. He performed the Cathode Ray tube experiment to prove hi model. -
Marie and Pierre Curie
Marie and Pierre Curie both discovered two elements by radioactivity in 1896. This proved a better understanding in radioactivity and the atoms and their unique properties. -
Henri Becquerel
Henri Becquerel was experimenting with an ore containing uranrium and found a accident that he left on a photographic plate without any light. Uranium was radioactive. -
Robert Millikan
Robert Millikan was born in 1868 and and determined the unit charge of the electron in 1909. He used the oil drop experiment at the University of Chicaco. He found out that the mass of the electron is equal to 1.60 x 10^-19 and that theey are positively charged atoms. -
Ernest Rutherford
Ernest Rutherford was born in 1871 and in 1911 he propsed the nuclear atom as a result of the Gold Foil Experment. He said that all of the positive charge atoms and mass is occupied by a small volume at the center of the atom and that most of the volume was empty space occupied by electrons. In 1920, he proposed the existence of the third atomic particle, the neutron. Bohr stated that Rutherfords idea of the electrons stays in clouds and the father you get the more electrons. He died in 1937. -
Quantum Model
The Quantum Model shows where one of the electrons are found. In 1923 Lous de Broglie suggested that oncethe electron moves with wavelength that will complete a circle which would exlpain the different energy levels as Bohrs model. It includes the nucleus as neutral particles and the protons as positive particles. -
James Chadwick
James Chadwick was a British phycisits that came up with the neutrons in 1932. He said that he neutron is a particle found in all nuclei of mass number greater than 1 and pocesses spin. He said that they help stabalize the nucleus. The discovery of the neutron led to the discovery of fision and ultimately to the atomic bomb. He died in 1974.
