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400
Democritus
Democritus dicovered that all matter is constructed of "invisible" particles called atoms, that these atoms are solid, they are homogeneous, and they differ in size, shape, mass, position, and arrangement. -
400
Democritus Atomic Model
Democritus believed that the atom was the absolute smallest piece of matter, no questions asked. -
John Dalton
John Dalton believed that all matter is composed of atoms, all elements of the same kind are identical (meaning they have the same mass), and that atoms are indestructible and retain their identity through chemmical reactions. -
John Dalton's Experiment
He performed a series of experiments on gases to determine what effect properties of the individual gases had on the properties. While explaining the results of those experiments, Dalton developed the idea that the sizes of the particles making up different gases are different. -
Robert Milliken
Robert Milliken determined the charge of an electron, and explored the photoelectric effect. -
Ernest Rutherford
Responsible for many discoveries in the fields of radioactivity and nuclear physics. -
Neils Bohr
Investigated the structure of the atom and the radiation emitting from it.
He also proposed that electrons are arranged in concentric circular orbits around the nucleus. -
JJ Thomson
He discovered the electron using a series of experiments designed to study the nature of electric discharge using the high-vacuum cathode ray tube. -
Geiger-Marsden Experiment
This was a series of experiments in which it was discovered that every atom contains a nucleus and most of its mass is concentrated. -
Oil Drop Experiment
Robert Milliken used a tiny submillimeter drop of oil suspended between capacitor plates to measure the incremental charge on an electron. -
Cathode Ray Tube Expirement
The Cathode Ray Tube was used by JJ Thomson when he discovered the electron. He interpreted the deflection of the rays by electrically charged plates and magnets and found “bodies much smaller than atoms” and later discovered the charge of these bodies. -
Bohr Experiement
He combined the atomic model of Rutherford with existing quantum theory Bohr Radius: (52.9 × 10 −12 m)
Bohr Magneton: (9.27 × 10 −24 J/T) -
James Chadwick
James discovered the neutron and helped develop an accurate atomic model for scientists to use. -
Beryllium Experiment
Bombarded beryllium atoms with alpha particles and produced unknown radiation. Chadwick saw this radiation was made of neutrally charged particles with the same madd of a proton. This particle became known as the neutron.
