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Oct 7, 1000
Aristotle 300 B.C
300 B.C - He made a theory that stated there are only four types of matter; fire, water, Earth, and air. He also believed there were four qualities to these: dryness, hotness, coldness and moistness.This was used for nearly 2000 years until scientists ruled this theory out. -
Oct 7, 1000
Democritus 430 B.C
(460B.C-370B.C) hH suggested that the universe is composed into two elements: both atoms and the void in which they exist and move. His theory re-emerged in the early 19th century in order to explain many laws that had been made in the previous century, when scientists had begun to measure the mass of reactants and products. -
John Dalton
(1766-1804) He made the Atomic Theory that says all matter is composed of atoms and that they are all small and indivisible. He also thought that a reaction was a rearrangement of the atoms. His theory was a little less involved than the modern atomic theory. -
Henri Becquerel
(1852-1908) He discovered radioactivity because he realized the chemicals decompose and give off pentrating rays. He also discovered that uranium containing minerals produced x-ray radiation. -
J.J. (Joseph John) Thomson
(1856-1940) He did an experiment with glass tubes and electricity causing him to discover the electron. J.J Thomson's experiments and hypotheses were re made by experimental work by many other scientists in the United Kingdom, Germany, France aswell as other places. -
Marie & Pierre Curie
Marie-(1867-1934) Pierre-(1859-1906), They discovered the radioactive elements polonium and radium. Marie made up the term radio activity. Marie won Nobel Prizes in both physics and chemistry for their work. Pierre couldn't accept the prize with her because he had passed away. One piece of their work has been in the treatment of cancer with radiation. -
Period: to
atoms
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Robert Millikan
(1868-1953) He discovered the mass of electrons by putting oil droplets in a magnetically charged field. He tested many ideas because he was an American Physist Professor. -
Ernest Rutherford
(1871-1937) He showed that the atom consisted of a positive nucleus and he also stated that negative electrons were in orbit around the nucleus. "Plum Pudding" -
Niels Bohr
(1885-1962)He proposed the Bohr Model. This created the symbol for atomic theory. "planetary model". He applied quantum theory to Rutherford's atomic structure by assuming that electrons travel in orbits defined by their momentum. This led to the calculations of possible energy levels for these orbits and the showing of light when an electron moves into a lower energy orbit. -
Quantum model
The Quantum model includes a nucleus containing neutral particles known as neutrons and positive particles called protons. -
James Chadwick
(1891-1974) He proved Rutherford's theory and discovered a third type of subatomic particle, which he named the neutron.
