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400
Democritus - 4000BCE
Democritus’ atomic theory has multiple parts to it. He concluded that there is empty space between atoms, atoms will always be in motion and atoms are not all the same size. He also theorised that atoms cannot be destroyed and there is an infinite number of atoms. http://plato.stanford.edu/entries/democritus/
https://www.emaze.com/@AOCRIIFR/atomic-theory -
Period: 400 to
Time Span
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John Dalton - 1803-1810
John Dalton had many elements to his atomic theory. Dalton concluded that all atoms of the same element are the same size and mass. He also concluded that atoms can combine to form compounds and that atoms of two different elements can combine to form multiple compounds, when in different rations, such as Water (H2O) and Hydrogen Peroxide (H2O2). http://www.columbia.edu/itc/chemistry/s0001/presentations/5-6.pdf
http://www.everythingmaths.co.za/science/grade-10/04-the-atom/04-the-atom-02.cnxml -
Period: to
John Dalton
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Joseph John (J.J.) Thomson - 1897
JJ Thomson conducted experiments resulting in a conclusion that Cathode rays contain electrons, which have electrical charges. This allowed him to conclude that atoms contain electrons. http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-bio.html
http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-facts.html -
Marie Curie - 1902
While Marie Curie was investigating the radioactivity of uranium, she was able to conclude that the ability to be radioactive depends on the interior of the atom. Curie also discovered that the amount of radiation that could be emitted depends on the total Uranium or Thorium contained in the atom. http://www.nobelprize.org/nobel_prizes/themes/physics/curie/ http://chem.arch.ug.edu.pl/kars/ABC-MSCurie.pdf -
Ernest Rutherford - 1910
While conducting research into how Alpha particles scatter, Ernest Rutherford was able to assume that there is a nucleus inside an atom. Rutherford has also concluded that all of the positive charges of an atom are concentrated in the centre. http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html
http://www.britannica.com/science/Rutherford-atomic-model -
Niels Bohr - 1913
Niels Bohr theorised that electrons move around the nucleus in prescribed orbits. He also theorised that when electrons move to another orbit that has a lower amount of energy, a light with a fixed wavelength is emitted. Bohr concluded that radioactivity depends on the structure of the nucleus. http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html
http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-lecture.pdf
