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Period: 500 to 550
Democritus
First person suggest that matter could not be infinitely divided. He made the term atomos to describe the tiny particles that make up matter and that move through empty space." Atoms can not be created destroyed or further divided. -
Period: Aug 24, 600 to Aug 24, 650
Aristotle
Disagreed with Democritus idea that atoms move threw empty space. Completely denied the existence of atoms due to personal idea about nature. His idea about matter took over those of Democritus back to square one. -
Period: to
John Dalton
School teacher that modern the atomic theory. He revises Democritus idea based on personal scientific research."Atoms are the smallest particales of matter and are indivisible and indestructible". -
Period: to
Sir William Crookes
noticed a green flash of light within a cathode ray tube while working in a dark laboratory. He noticed some type of radiation striking a zinc-sulfide coating inside the tube.Later discovered that the radiation went completely through and not only the Zn-s coating. Dobbed these "cathode rays" this discovery led to the TV. -
Period: to
Physicists J.J Thompson
He designed CRT experiments at Cambridge to determine the ratio of the particle's change to its mass. Concluded that mass of the particles was much less then that of the hydrogen atom which disproved Dalton's theory that atoms were indivisible. He revived the Nobel prize in 1906 for his research in the discovery of the electrons. -
Period: to
American Physicist Robert Millikan
He designed an oil drop apparatus to determine the charge of electrons. Determined that the magnitudes of the charge of the electrons was 1.602x10^-19 Coulomb's. The charge was equal to a negative charge, so the electron carries a charge of negative 1. He discovered the mass of the electron using the unknown charge/mass vatio : 9.1x10^-28g. -
Period: to
Ernest Rutherford
He studied positively charged a-particle's. He did an experiment that concluded that Thomson plum pudding model of the atom was incorrect. Rutherford calculated that an atom was mostly just empty space for electrons to move around and he came up with , that in the atom there is a tiny spot called the nucleus. His theory was that the negatively charged electrons were attracted to the positively charged nucleus.