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Period: 300 to
Timeline
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460
Democritus
460 - 371 B.C.
Democritus was an ancient Greek philosopher who believed that all matter consisted of extremely small particles that could not be divivded. He called the particles Atomos, meaning "indivisible" or "uncut" -
John Dalton
Late 1700's
John Dalton was a school teacher in England. He based his conclusion on experimentation and observations. He created the Atomic Theory. His theory states that: All elements are made of submicroscopic indivisible called atoms, Atoms of the same element are identical and atoms of different elements are different, atoms of different elements combine in whole number ratios to form compounds, chemical reactions involve the rearrangement of atoms and no new atoms are created or destroyed. -
Sir Joseph John Thomson
1856-1940
Thomson was conducting experiments with vacuum tubes. (CRT'S)
He modified his tube to contain a cathode (-) and an anode (+). Later, he added a paddle wheel and a phosphorus plate. -
Robert Milikan
1868-1953
Milikan was a nobel Laureate in physics because of his discovery of the mass of an electron. He was the president of Caltech for 24 years. In 1909, he conducted an experiment to determine the mass of the electron. -
Ernest Rutherford
1871-1937
Ernest Rutherford discovered the charge and mass of the proton. He conducted an experiment where he used a radioactive material to give off alpha particles to a piece of gold foil. He surrounded it with a phosphorus screen and noticed flashes of light every once and a while. He then noticed them going back to the source of the radioactive material. He then concluded that there must of been a positive particle that allowed it to reflect off of the gold nucleus. -Aerial view of the atom -
Niels Bohr
1885-1962
Bohr stated that electrons had orbits about the nucleus. This was the Planetary Theory. -
James Chadwick
1891-1974
Chadwick became an English Nobel laureate due to his discovery of the charge and mass of the electron. He concluded that the neutron was neutral and that it has a mass of 1. -
Aristotle
384 - 322 B.C. (300's B.C)
Aristotle was another Greek philosopher who was a pupil of Plato for twenty years. Aristotle believed that all matter came from only 4 main elements: earth, air, fire, and water. He also believed that everything else came from Aether. (planets, stars, and the Sun)
