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360
Democritus
Democritus' theory was that all matter consists of invisible particles called atoms, atoms are indestructible, atoms are solid but invisible, atoms are homogenous, and atoms differ in size, shape, mass, position, and arrangement. He proved this model was accurate by providing accurate evidence. -
400
Aristotle
Aristotle provided the theory that water, Earth, air, and fire are the four basic elements of life. There was no experiment to prove this but many people agreed with the theory. -
John Dalton
John Dalton's atomic theory included that all matter is made of atoms, atoms are indivisible and indestructible, all atoms of a given element are identical in mass and properties, compounds are formed by a combination of two or more different kinds of atoms, and chemical reactions are a rearrangement of atoms. Dalton composed a table listing the atomic weights of all the known elements and his atomic theories were then soon adopted by the scientific community with few objections. -
Henri Becquerel
Henri Becquerel is known for his discovery of radioactivity. His evidence was shown when he was studying the effect of x-rays on photographic film. -
Robert Millikan
Robert determined the unit charge of the electron with his oil drop experiment. This allowed for the calculation of the mass of the electron and the positively charged atoms. -
J.J Thomson
Thomson identified the negatively charged electron in the cathode ray tube experiment. He concluded that the electron was a component of all matter and calculated the charge to mass ratio for the electron. -
Ernest Rutherford
Rutherford proposed the nuclear atom as the result of the gold-foil experiment he enacted. He proposed that all of the positive charge and all of the mass of the atom occupied a small volume at the center of the atom and that most of the volume of the atom was empty space occupied by the electrons. -
Neils Bohr
Bohr displayed an atom which was 1/10,000 the size of the atoms proposed by other scientists. He also described the nucleus as a compound structure. -
Quantum Model
The quantum mechanical model is based on mathematics and can be used to explain observations made on complex atoms. The quantum mechanical model is based on the quantum theory, which states that matter also has properties associated with waves. The Quantum Theory shows that it is impossible to know the exact position and momentum of an electron at the same time. This theory is not proven to be true. -
James Chadwick
James Chadwick proved the existence of neutrons. He proved that neutrons play a key part in nuclear fission, or the splitting of atoms by putting a piece of beryllium in a vacuum chamber with some polonium.The polonium then emitted alpha rays which struck the beryllium, which caused the beryllium to emit the mysterious neutral rays. -
Marie and Pierre Curie
Marie and Pierre helped Henri Becquerel with the discovery of radioactivity. The experiments they did proved that the radiation of Uranium compounds can be measured with precision under determined conditions, and that this radiation is an atomic property of the element of Uranium.
