history of the atomic model
By hibaby, Updated
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and thus an atom
His mentor, Leucippus, originally came up with the atomic theory, but it was then adopted by Democritus. The atomic theory stated that “The universe is composed of two elements: the atoms and the void in which they exist and move.” According to Democritus atoms were miniscule quantities of matter.
Democritus first suggested the existence of the atom but it took almost two millennia before the atom was placed on a solid foothold as a fundamental chemical object by John Dalton Although two centuries old, Dalton's atomic theory remains valid in modern chemical thought. All matter is made of atoms.
In 1897, J.J. Thomson discovered the electron by experimenting with a Crookes, or cathode ray, tube. He demonstrated that cathode rays were negatively charged. ...Thomson realized that the accepted model of an atom did not account for negatively or positively charged particles.
Electron Cloud Model
Rutherford overturned Thomson's model in 1911 with his well-known gold foil experiment in which he demonstrated that the atom has a tiny and heavy nucleus. Rutherforddesigned an experiment to use the alpha particles emitted by a radioactive element as probes to the unseen world of atomic structure.
In 1913, Niels Bohr proposed a theory for the hydrogen atombased on quantum theory that energy is transferred only in certain well defined quantities. Electrons should move around the nucleus but only in prescribed orbits. When jumping from one orbit to another with lower energy, a light quantum is emitted.
Atomic Theory. Austrian physicist Erwin Schrödinger (1887-1961) developed an “Electron Cloud Model” in 1926. It consisted of a dense nucleus surrounded by a cloud of electrons at various levels in orbitals.
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