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Democritus: about 460-370 B.C.E.(should be before this date)
Democritus had the idea that there were tiny particles called atoms that made up everything in existance. Democritus believed that atoms could not be split. He also believed that the aomunt of atoms were infinite. His overall theory led to the idea of atoms that was developed upon, yet some areas were also quite wrong. Aristotle didn't agree with this theory and beleived it to be wrong. The exact date it was adopted was unknown, yet it was believed to have been around 400 B.C.E. -
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Aristotle Picture (384-322 BCE)
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Democritus Picure (about 460-370 BCE)
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Aristotle 384- 322 B.C.E. (should be before this date)
Aristotle believed that everything in the world consisted of and was made from fire, air, earth, and water. He considered these the elements of the world. There were also the forces of hotness, dryness, coldness, and wetness in his theory. This began the thought that everything was made of something smaller, eventually developing into the idea of the atom and element. Aristotle did not agree with Democritus, and their idea conflicted. His idea was adopted somewhere around 360 B.C.E. -
Antoine Lavoisier
As well as discovering the law of conservation of mass, supporting Democritus' idea of atoms not being created or destroyed. He also played a big part in the atomic theory. He was one of the first to create a table of elements, and classified elements based on they're properties. His periodic table was adopted in the late 18th century. -
Antoine Lavoisier Picture
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John Dalton
He beleived that atoms could not be seperated and were indestructable. He beilved that every atom had its own individual properties. He also theorized that compounds were a combination of atoms, and that chemical reactions were rearrangements of atoms. He contradicted Aristole because he thought there were more than 4 elements. He used Laviosier and Democritus' ideas to create his theory. The year that this was belived to have been adopted was 1803. -
John Dalton Picture
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Henri Becqerel
He was a chemist that was interested in x rays, and used infa-red in many of his discoveries. Upon experimenting, he accidentally discovered radiation. This was important due to radiation being the changing the sub atomic particles, leading to further discovery of them. This also showed the results of affecting an atom. He accepted the Nobel Prize with Marie and Pierre Cuire. His theories were adopted in 1896. -
Henri Becqerel Picture
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J.J. Thomson
J.J., the teacher of Rutherford, was credited with the discovery of the eletron, using a cathode ray tube and a positively charged plate, watching them bend towards the plate. This discovery of the negatively charged electrons further develeoped the structure of the atom. The model was called the plum pudding model with the "plum" neutrons in the positive "pudding". His theory was adopted in 1898. -
J.J.Thomson Picture
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Max Planck
Max discovered that on such a small level, energy was found in bundles or packets of energy, An example of this is when an eletron jumps between levels, it needs a certain amount or bundle of energy to instantly jump, or else it won't. He also discovered that light was emitted from this descent in jumping, resulting in the further development of light. This helped to eventually develop the Bohr's model. It was adopted about 1900. -
Max Planck Picture
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Marie and Pierre Curie
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Marie and Pierre Curie
Marie and Pierre Curie were in the development of the understanding of radiation, and even discovered polonium and radium. They discovered that the radation level depended on the amount of material. Theydiscovered that if, in an atom, the particles were changed, the atom would change and potentially enter a radioactive state. This showed what what happened when you messed with the sub atomic particles in the atom. They shared a Nobel Prize with Henri Becquerel. Thier idea was adopted in 1898. -
Robert Millikan
Milikan conducted an experiment by puttting a very tiny drop of oil between two plates that were charged. He used the time taken for the oil to drop and subtracted out gravity in order to get the mass to charge ratio for electrons. This was significant becuase it developed upon J.J. Thomson's ideas to lead to more information about electrons. The year this was adopted was approximately 1908. -
Robert Millikan Picture
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Ernest Rutherford
Ernest Rutherford, a student of J.J. Thomson, discovered that there were negatively charged particles (electrons). He beleived that much of the atom was just space, and the nucleus was what was responsible for almost all the mass. He used a gold sheet, finding much of it pass through, proving that the atom mainly consisted of space. The model was used in 1909. This discovery was important because it showed that the nucleus was an obvious part of the atom. -
Ernest Rutherford Picture
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Niels Bohr Picture
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Niels Bohr
He created the model of the atom that is still is used today (Bohr's model). The diagram consists of a small center made of various cicles (nucleus) which was surrounded by rings that had electrons on them. The rings represented the orbit or path of the electrons on that level. The orbit was the same distance around the nucleus the entire time. He used Planck's quantized energy theory to help develop his model. He looked up to Rutherford throughout his studies. His model was adopted around 1913. -
Erwin Schrodinger
Erwin created a new model called the quantum mechanical model. In comparison to the previous models, it didn't define the location of the electron, but suggested that the nucleus was surrounded by an "electron cloud", affecting the Bohr model. This model predicted the odds of the electron going to that specific area as shown. Erwin created equtions to find the area that the electrons could be. This theory was adopted in 1926. -
Erwin Schrodinger Picture
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Henry Moseley
He discovered that all the elements had atomic numbers based on the number protons and neutrons in the element. He arranged the periodic table based upon the atomic numbers of the elements, which made it much clearer and understantable, as well as being more logical. He also created Moseley's law, saying that the atomic number and energy are directly related. His theory was adopted about 1915. -
Henry Moseley Picture
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James Chadwick
James, a student of Rutherford, was credited with the discovery of the neutron in an atom. Unlike the pervious belief that there were only protons and electrons that cancelled each other out, he believed that there was more to the atom; especially due to the atomic mass and atomic number not matching up. The neurtrally charged particles he discovered were called neutrons. His discovery made Bohr's model more accurate. His idea was adopted about 1931. -
James Chadwick Picture
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Werner Heisenberg
Werner, in comparison to other belief at that time, thought that elctrons didn't travel in oribts, instead they were found in clouds that were relative to where they were. It was called a cluod because the location of the electrons in that area was constantly changing, so it is just considered a cloud. He still believed that quantized energy theory was possible, just it was not that direct. His theory was adopted about 1927. -
Werner Heisenburg Picture
