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Period: to
Atomic Theory Years
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John Dalton's Solid Sphere Model
"1) All matter is made of atoms. Atoms are indivisible and indestructible."
"2) All atoms of a given element are identical in mass and properties."
"3) Compounds are formed by a combination of two or more different kinds of atoms."
"4) A chemical reaction is a rearrangement of atoms." -
Joseph John Thomson's Plum Pudding Model
Thomson "discovered the electron" while performing "experiments designed to study the nature of electric discharge in a high-vacuum cathode-ray tube." He "estimated the value of the charge" ("very large value for the charge-to-mass ratio") of these bodies that are "much smaller than atoms". -
J.J. Thomson continued
Thomson also decided upon "a model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces." -
Ernest Rutherford's Nuclear Atomic Model
Rutherford performed the Gold Foil Experiment, in which he attempted to have alpha particles go through a piece of thin gold foil. Although most particles went through, some did not. This finding pushed him to decide that an atom has "a central positive nucleus surrounded by negative orbiting electrons." "Most of the mass of the atom was contained in the small nucleus, and that the rest of the atom was mostly empty space." -
Neils Bohr's Solar System Atomic Model
Bohr found out that "only certatin colors of light are given off" "when electrons are exposed to flame or electric fields." Electrons are in orbits of differing distances from the nucleus (comparable to "planets orbiting the Sun"), and light is emitted when electrons move from an outer orbit to an inner orbit. -
Ernest Rutherford's Proton Atomic Model
Rutherford continued his experimentation with alpha particles and found that "small positively charged particles" could be knocked off of an atom by the alpha particles. He called these particles protons. -
Erwin Schrodinger's Equation
Schrodinger said that you can "predict the properties and reactivities of all atoms and molecules" using his equation: (Hamiltonian X Orbital = Energy). -
Werner Heisenberg's Uncertainty Principle
Heisenberg concluded that "observation requires light, and light has momentum", so "the location and velocity of small particles such as electrons" can not be precisely specified. -
James Chadwick's Atomic Theory
Chadwick discovered that protons were not the only particles in the nucleus of an atom. He found that neutral particles, neutrons, hold "positively charged protons together." -
Modern Atomic Model: The Electron Cloud
The Modern Atomic Model, or the Electron Cloud Model, uses mostly the experiments and conclusions conducted by Erwin Schrodinger, Werner Heisenberg, and James Chadwick. This model shows that electrons can not be located specifically. Rather, "the electron cloud indicates where you will most likely find a single electron."
