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Period: 370 to
History of the Atom Timeline
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400
Aristotle
Aristotle- believed matter was created by 4 elements: fire, earth, water, and air. He thought that however many times you cut a form of matter, you'll always have a smaller piece. Aristotle's theory was used for almost 2000 years, until after the scientific revolution.The scientific method was developed to explain Aristotles theories and experiments he came up with. -
400
Democritus
Democritus (460-370 BC) believed that matter was created by indivisible particles called atoms. Color, taste, and other intangible things were also thought to be made up of atoms. -
John Dalton
John Dalton came up with the Law of Multiple Proportions. This was to help better understant his theories. He is known for the development on the atomic theory in 1803. Dalton did experiments with different temperatures, gasses and vapors. -
Henri Becquerel
In 1896, Henri Becquerel discovered radioactivity while studying the effect of x-rays on photographic film. He won the nobel prize in 1903 for his discovery. -
J.J.Thomson
Joseph John, or J.J. Thomson, identified the negatively charged electron in the cathode ray tube. Thomson created the "plum pudding" model of the atom. He also said that rays were made up of very light and negatively charged particles that were blocking the atoms. -
Ernest Rutherford
In 1909, Rutherford found that all of the positive charge and mass of of an atom was located at the center of an atom. He used the Gold Foil Experiment where he shot particles at gold foil expecting them to go through but instead, they bounced back. This proved the existence of the nucleus. -
Marie and Pierre Curie
The Curie's spent much of their careers studying radioactivity and examining the particles and energy produced. In the process they discovered matter.They knew that the element thorium was radioactive and found two new elements, polonium and radium. They developed the idea of radioactivity due to their research -
Robert Millikan
Millikan determined the charge of the electron with his oil drop experiment at the University of Chicago. It allowed for him to calculate the mass of the electron and the mass of the positively charged atoms.This proved the mass of an electron is 1000 times smaller than the smallest atom. Harvey Fletcher helped him with this experiment. -
Niels Bohr
In 1922, Bohr came up with the planetary model. He believed that electrons orbited the nucleus just like planets orbit the sun. He also developed an explanation of how the atomic structure effects the regularities of the periodic table of elements. -
Quantum Model
The Quantum model is the most up to date theory on atomic structure. It explains the stability of the electrons surrounding a nucleus. It includes the nucleus, electon, neutron, and the proton in the atom. All past experiments and theories have proved or lead up to the Quantum Theory. This theory was developed by C.J. Davisson and I.H Germer. -
James Chadwick
In 1932, Chadwick discovered an unknown particle by the lack of electric charge in the atomic nucleus. The idea of the neutron had earlier been proposed by Rutherford. Chadwick, however, tested this theory and experimented by using a sample of Berrylium with alpha-particles, which emits radiation. The electrons and protons cancelled each other out.
