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400 BCE
Democritus
He was a central figure in the development of the atomic theory
Had a theory that material bodies are made up of small atoms -
Period: 400 BCE to
Chapter 4 timeline
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John Dalton
Developed methods to calculate atomic weights and structures and formulated the law of partial pressures
Contributed to the atomic theory by hypothesizing that the law of conservation of mass and the law of definite proportions could be explained using the idea of atoms -
Eugen Goldstein
Discovered that protons have an equal and opposite charge as an electron
Known for his work on electrical phenomena in gases and on cathode rays; he is also credited with discovering canal rays -
J.J Thomson
Discovered the electron
Demonstrated that cathode rays were negatively charged
Proposed the plum pudding model of the atom, which had negatively-charged electrons embedded within a positively-charged "soup. -
Ernest Ruthford
Discovered the nucleus of the atom
Designed an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure(Rutherford gold foil experiment) -
Robert Millikan
Millikan conducted the oil drop experiment The experiment helped to quantify the charge of an electron, which contributed to the understanding of the structure of the atom and atomic theory -
James Chadwick
Proved that it consisted of a neutral particle with about the same mass as a proton
Chadwick measured its mass
