History of Atmomic Theory

Democritus
Proposed the idea of indivisible particles called atomos
Joseph Priestley
Discovered Oxygen
Antoine Lavoiser
Law of Conservation of Matter, Mass of Reactants = Mass of Products
Joseph Proust
Law of Definite Proportions, The proportion by mass of the elements in a given compound is always the same.
John Dalton
Atomic Theory
Jakob Berzelius
System of symbols for elements
Heinrich Giessler
Made the first vacuum tube.
Sir William Crookes
Used a vacuum tube to discover what are now called cathode rays
Eugene Goldstein
Discovered the existence of charges particles
Willhelm Roentgen
Discovered the existence of X-Rays
Henri Becquerel
Discovered the existence of radioactivity
J.J. Thomson
Discovered cathode rays to be electrons. Measured charge to mass ratio of electrons. Plan-pudding model of atom. Electrons implanted in sphere of solid charge. Atom is neutral. Mass of atom is evenly distributed.
Robert Millikan
Famous oil drop experiment in which he measured the charge of an electron to be 1.6×10^(-19) coulombs. Used the charge to mass ratio found by Thomson to find the mass of the electron to be 9.1×10^(-28)g.
Ernest Rutherford
Gold Foil Experiment in which he discovered the nucleus of the Atom. He attributed the deflection of alpha particles to the concentration of positive charge and mass at the center of the atom. Planetary Atomic Model. Positively Charges nucleus containing the mass of the atom with electrons orbiting the nucleus at high speeds. The Electrons are equal in number to the positive charge of the nucleus.
Henry Moseley
Developed atomic number concept
F.W. Aston
Discovered the existence of isotopes
James Chadwick
Discovered the electrons. It was named and predicted by Rutherford.
Max Planck
Quantum theory of light-Light exists in small energy packets called quanta or photons.
Louis DeBroglie
Particles(like electrons) can have a wave-like character
George P. Thomson
Confirmed DeBroglie’s ideas experimentally. He found that when directing a stream of electrons at a diffraction grating the same results were obtained as were obtained with light.
Werner Heisenberg
Heisenburg Uncertainty Principle. It is impossible to know both the location and velocity of an electron at the same time
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