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Jan 1, 1000
Aristotle 400 BCE
Aristotle believed that everything was made of four elements and had four qualities. This contradicted with what was previously believed.This idea/model was used for close to 2000 years. -
Jan 1, 1000
Democritus 400 BCE
Democritus stated that all things are made up of atoms, which are indivisible and indestructable. They are also always in motion and always will be in motion. Also, they differ in size and shape. -
Period: Jan 1, 1000 to
The Atom
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Antoine Lavoisier
In 1774, Lavoisier began studying the burning process. He proposed the combustion theory and the law of conservation of mass. The only contribution to the atom he really had was that he discovered that water was made of hydrogen and oxygen and that a couple of other things were made of carbon. His work helped Dalton some to make his model. -
John Dalton
Dalton's theory was that every element was made up of different atoms, specifically with different masses. He also said that compounds are made of atoms of different elements combined. These ideas were revolutionary and many are still used today. His model was quite simple, it just looked like a marble. -
JJ Thomson
JJ Thomson conducted an experiment with a cathode ray tube, not uncommon at the time. He interpreted that the deflection of rays by magnets as evidence of particles much smaller than atoms. That particle being the electron. In 1904 he made the plum pudding model of the atom. -
Max Planck
Planck didn't have much to do directly with the model of the atom, but his idea of quantum mechanics, which he first came up with while studying Blackbody Radiation in 1897. The first model to use his quantum mechanics was Bohr's. -
Henri Bacquerel
Bacquerel discovered that rays emitted by uranium differ from X-Rays, in that they could not be detected by electric or magnetic fields. For the discovery of this spontaneous radioactivity he go half a nobel prize, to be shared with the Curies. -
Pierre and Marie Curie
Marie Curie was the main discoverer in this. They won a nobel prize for the discovery of radioactivity with Bacquerel. Marie during WWI devoted her time for the use of X-Rays in medicine. -
Robert Millikan
Millikan figured out how to get an electrons mass by doing a famous experiment with Thomson. It was call the "Oil Drop experiment" and was the first attempt to measure the effect of an indivisual subatomic particle. -
Ernest Rutherford
Rutherford tested Thomson's plum pudding model. To do so he shot alpha particles at gold foil. As expected most of them went through, but some bounce right back. This showed that the plum pudding model was not accurate. He then made the first version of the planetary model. -
Neils Bohr
Bohr applied the quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits. This led to the calculation of energy levels. -
Henry Moseley
Moseley studied under Rutherford and developed the application of X-Ray spectra to study atomic structure. This led to more accurate positions on the periodic table. In 1913 he discovered that there are different isotypes of certain atoms. -
Erwin Schrodinger
Schrodinger published four papers in 1926 that talked about his new theory for wave mechanics in electrons. The next year he took Max Planck's spot at the University of Berlin. -
Werner Heisenberg
Heisenberg is known for the uncertainty principle, which restricts the accuracy with some properties of atoms and particles that can be determined. He published these ideas in his book in 1928. -
James Chacdwick
Chadwick discovered the neutron. This was crucial to fission of Uranium-235, which led to the creation of the atomic bomb.
