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Period: 300 to
atomic theory timeline
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360
Democritus
Democritus's theory was that all matter consists of invisible particles called atoms, atoms are indestructable, atoms are solid but invisible, atoms are homogenous, and atoms differ in size, shape, position, arrangement. He proved this model was accurate by providing accurate evidence. -
400
Aristotle
Aristotle provided the theory that wind, water, fire, and air are the four basic elements of life. There were no tests done his theory just prevailed because people understood his philosiphy and liked it better than Democritus's. -
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 worked with the properties of the atom, like radioactivity. His biggest achievements were in the field of radioactivity. He experimented with light and the absorption of light by crystals. When experimenting with an Uranium ore he accidently found that leaving the ore on a photographic place without any light that the ore left an image. Henri discovered that this occured because Uranium is radioactive. This discovery of radioactivity allowed later scientists to perfect the atomic model. -
Marie & 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. -
Robert Millikan
Robert Millikan has a theory with electrons. He proved electrical charge, which is carried by an electron.Millikan performed an experiment based on an Thomson's earlier attempt, but used charged oil drops instead of charged water drops. -
Ernest Rutherford
Rutherford shot alpha particles at gold foil, thinking they were going to go right through the foil. Most of them did go right through the but some others were reflected meaning that there was a small, dense positive charged area which he called the nucleus of an atom. This experiment was called the goil foil experiment which was done in 1908 -
J.J. Thompson
He discovered the electron and his expeirement was called "Plum Pudding". Thomson attempted an experiment where he observed the behavior of falling charged water drops. This experiment, was inaccurate because the water drops evaporated during the experiment, and Thomson could only estimate how fast they evaporated in order to interpret the results. Robert Millikan changed Thomson's throury by using oil doprs instead of water so it didn't evaporate as quickly. -
Niels Bohr
Bohr's model was known as the "plantetary model"In the Bohr Model the neutrons and protons occupy a dense central region called the nucleus, and the electrons orbit the nucleus much like planets orbiting the Sun. -
Quantam 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
Chadwick proved the existence of nuetrons. This resulted in the solution for the hidden mass in the atoms which led to the investigation of the nature of the nucleus and its forces. This made Chadwick recieve the Nobel Prize for Physics in 1935.
