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Oct 25, 1000
Democritus (450 BC)
Democritus discovered there was an existance of the atom. His theory was that if you cut down matter into smaller portions it would eventually get down to a size that could not be broken down anymore. The smallest piece that would be obtained and invisible to the eye would be the atom or the atomos as Democritus had called it. -
Oct 27, 1000
Aristotle (450 BC)
Aristotle's theory stated that "all matter is made up of four elements". The four elements would be earth, fire, water and wind. He also stated there was four qualities to the elements. The qualties were dryness, hotness, coldness, and moistness. -
Oct 26, 1234
Marie & Pierre Curie
They were a married couple who discovered Polonium and the famous element Radium. They contributed to the atomic theory by discorvering the mass of the atom. -
John Dalton
John Dalton was called "the father of the atomic theory". He thought the atom was a dense sphere. His atomic theory consisted of five parts. The five postulates are atoms make up elements, atoms of the same element are identical, atoms of different elements are different, atoms of different elements react to form compounds, and atoms can not be created or destroyed; they can olny be changed. -
J.J Thomson
J.J. Thomson discovered the existence of the electron. He used the cathode ray tube expirement. This expirement collected all of the positive particles. But there was still a charge passing through the tube. Seeing that the magnet collected all the positivly charged particles means it left a negatively charged particle. They later established this particle as the electron. -
Robert Millikan
Robert Millikan discovered the mass and charge of the electron. He discovered this by using the Oil Drop Expiriment. This expirement was set up so that the rate at which the oil droplets fell, Millikan was able to measure the mass of the oil droplets. The electrial charge on the droplets was aquired by collision with gaseous ions. By doing this he found out the mass and charge of the electron, -
Ernest Ruthoford
Ernest Ruthoford found out that the neculus existed. He found out by using the gold foil expirement. His theory was the e-cloud model. By all the electrons being around this very small, dense, positive center. Ruthoford called this the nucleas. -
Niels Bohr
Neils Bohr atomic theory was the planatary model. This model was that the protons and nuetrons were very dense in the middle. They make up the nulecus. The electrons surrond the nulecus almost like how the planets orbit the sun. -
Henri Becquerel
Henri Bacquerel discovered uraniam and its radioactive proporties. When x-rays were discovered, Henri noticed that the x-rays were giving off by uranimum salts. He set up an expirement to see if theyre was such thing as radioative properties and he was right. He was awarded a nobel prize for what he had discovered. -
James Chadwick
James Chadwick discvered the nuetron. He proved there was an existence of nuetrons by seeing that the nuetron plays a big part in the splitting of an atom. -
Quantum model
The quantum model of the atom is the one we use today. Neils Bohr's planatary model has led tp this one
