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Jan 1, 1000
Democritus
Democritus was the first person to suggest that matter could not be divided infinietly. Made the term atomos, which later became atom, to describe the tiny particles that make up matter and that move through empty space. He couldn't figure out what holds atoms together. He also said atoms cannot be destoryed, further divded, or created. -
Jan 1, 1001
Aristotle
Disagreed with Democritus' idea that atoms move through empty space. Denied the exsistence of atoms due to personal ideas about nature. His ideas took over those of Democritus - back to square one. -
John Dalton
Revived the "atom". He said that atoms are the smallest part of matter, and that they are indivisible and indestructable. His theory was widely accepted upon it's ability to explain the convservation of mass. -
Sir William Crookes
While working in a dark labortary he noticed a green flashing of light within a cathode ray tube. He discovered that some type of radiation was striking a zinc-sulfide coating inside the tube. He later found that the radition went completely throught the tube and not only on the Zn-S coating. He called these "cathode rays". This led to the discovery of the television. -
J.J. Thomson
He determined the ratio of the particles change to its mass. He concluded that the mass of the particle was much less than of the hydrogen atom. This disapproved Dalton's theory that atoms were indivisible. -
Ernest Rutherford
He concluded that Thomson's plum pudding model of the atom was incorrect. He calculated that the atom was mostly just empty space for electrons to move around in. He claimed it was contained in the centor of an atom and called that place the nucleus. His theory explained that negatively-charged electrons were held within the atom by their attraction to the positivley-charged nucleus. He determined that if the nucleus were the size of the ball of a fine-point pen it would weigh more than 70 cars. -
Robert MIllikian
He determined the charge of the electron by designing an oil drop appartus. He determined that the magnitude of the charge of the electron. He also discovered the mass of an electron by using the known charge/ mass ratio. -
James Chadwick
He demonstrated that the nucleus had another nuetral subatomic particle, this particle is the nuetron. He found out that the particle had no electric charge and weighs the same as a proton.
