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460
Democritus
Democritus was basically the first person to discover and name small particles called atoms. His dicovery led to many more contributions on the atomic theory -
Period: 460 to
History timeline of an Atom
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Antoine Lavoisier
He proposed the Combustion Theory which was used by sound mass measurements, he also proposed the Law of Conservation of Mass which was the begginning of modern chemistry. These discoveries led to the weighings of atoms. -
John Dalton
Proposed an atomic theory with spherical solid atoms based upon measureable properties of mass. He also proposed the Law of Multiple Proportions, which led directly to the proposal of the atomic theory. -
Henri Becquerel
He studied the x-rays on photographic film, he discovered some spontaneously decompose and give off very pentrating rays. he and the Curies discovered radioactivity. -
J.J. Thomson
He identified the negatively charged electron in the cathode ray tube. He deduced that the electron was a component of all matter, that calculated the charge to mass ratio for the electron -
Marie and Pierre Curie
The couple discovered the element polonium and radium. they won peace prizes in chemistry and physics. they were inspired by Becquerel's discovery of radioactivity and flourished on from there. -
Max Planck
Stated that energy is radiated into small discrete units, which he called quanta. He was able to deduce the relationship between the energy and the frequency of radiation -
Robert Millikan
Did an oil drop experiment determined the charge (e= 1.602*10-19 cloumb)and the mass (m=9.11*10-28 gram) of an electron. He also studied about forces that exert on one another, and the results produced by these forces. -
Henry Mosely
Using x-ray tubes, he determined the charges on the nuclei of most atoms. He stated that the atomic number of an element is equal to the number of protons in the nucleus. His work caused the periodic table to be reorganized, so that element can be based upon atomic number, not atomic mass. -
Ernest Rutherford
By using alpha particles as atomic bullets, probed the atoms in a piece of thin gold foil. He established that the nucleus was very dense, very small, and positively charged. He also assumed that electrons were located on the outside of the nucleus. -
Niels Bohr
He developed an explanation of the atomic structure that underlies regularities of the periodic table of elements. His atomic model had atoms built up succesive orbital shells of electrons. -
Werner Heisenberg
He proposed the Principle of Indeterminancy- you can not know the both the position and the velocity of a particle. -
Erwin Schrodinger
He explained movement of an electron in an atom as a wave. He also viewed electrons as continous clouds and introduced wave mechanics as a mathmatical model of the atom. -
James Chadwick
He measured the energy of the protons emerging from the hydrogen atoms. By using alpha particles, he discovered a neutral atomic particle with a mass close to a protons. This discovery became known as a neutron. -
Period: to
History of a Atom
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Aristotle
From 384-322, Aristotle stated that no matter how many times you cut a form of matter in half, you will always have a smaller piece of that matter left. Aristotle also discovered the four elements water, earth, air, and fire. using these elements he was able to cut down their forms of matter too.
