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450
Democritus
said that everything was composed of atoms. Claimed that all atoms are physically but not geometrically indivisible. Between every atom is an empty space. All atoms are always in motion -
Antoine Lavoiser
Studied the burning process. Proposed the combustion theory which was based on the sound mass measurements. He nemed Oxygen. -
Joeph Louise proust
Proposed the law of constant compostition. This was very radical at this time and was hotly contested by Claude Berthollet. -
John Dalton
proposed the law of multiple proportions. this llaw led directly to the proposal of the atomic theory. also developed the concept of the mole and proposed a system of symbols to represent atoms of different elements. He came up with a formula for water HO. Assignd a relative atomic weight of one to hydrogen and eveloped a relative atomic weight scale from percent composition data and assumed atomic ratios -
Dmitri Mendeleev
Proposed the peroidic law and developed the first peroidic table. his table was arranged according to the increasing atomic weight and left holes for elements that were not yet to be discovered. -
Eugene Goldstein
He named the cathode ray. the cathode ray later discovered to be composed of electrons and the canel ray: positive hydrogen ions that had been stripped of their electrons in a cathode ray tube. Those would later be named protons. -
J.J. Thomsen
Identified the negatively charged electron. He deduced that the eletron was a component of all matter and calcuated the charge to mass ratio for the electron. e/m= -1.76 x 10 ^ 8 coulobs/g -
Marie Curie
studied uranium and thorium and called their spontaneous decay proves " Radioactivity." Her husband and her discovered the radioactive elements polonium and radium. -
Robert Millikan
He determined the unit charge of the electron. Found the unit charge of the electron with ihis oil drop exeriment at the University of Cicago. this allowing for the calculation of the mass of the election and positively charged atoms. E= 1.60 x 10 ^ -19 -
Ernest Rutherford
Proposed the nuclear atom as the result of the gold-foil experiment. Also proposed that all of the positive charged and all the mass of the atoms occupied a small volume at the center o the atom and that most of the volume of the atom was empty space occupied b the electrons. -
Henry Moseley
proposed that the relationship was a function of the positive charge on the nucleus. Discovered that the enery of x-rays emitted by the elements increased in a inear fashion with ach successive element in the periodic table. -
Niels Bohr
Incorrecty modified the earlier Rutherford model's of the atom. His is important because of the accepted features of atomic theory without all of the high-level math of the modern version. -
erwin Schrodinger
Developed the equation which is used today to understand atoms and molecules. Took the ideas developed by De Brodlie. heisenberg and others put them together in a single equation. Solving this equation can principle predict the properties and reactivitivies of all atoms and molecules. Its extremely difficult to sole for any but the most simple atoms and milecules. -
James Chadwick
The existence of neurons, a non-charged paricle within the atom's nucleus. found out the atomic number was less than the mass. Found out what was in the atoms and the mass of the atoms. -
Lise Meitner
Conducted xperiment varifing that heave elements capture neutrons and form unstable products which undergo fission. This process ejects more neutrons continuing the fission chain reaction.