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420 BCE
Democritus
Democritus developed the intial idea of an atom. He believed that matter was made up of small invisible particles called atoms. -
390 BCE
Aristotle
Aristotle thought that Democritus was wrong about his atomic theory that the world was composed of small particles. He believed that the world was made up of air, water, fire and earth. -
John Dalton
Dalton did multiple experiments to prove that matter consisted of small particles called atoms. This lead to Dalton's Atomic theory. His model shows the fixed relations that connect atoms, but it does not show the forces which hold the atoms together in compounds. This theory was later discarded after JJ Thomson discovered the electron. -
Michael Faraday
Michael Faradsay discovered that matter has an electrical nature that consists of fixed quantities of electricity. -
Dimitri Mendeleev
Mendeleev created the first version of the periodic table. -
James Clerk Maxwell
He proposed the theory of electromagnetism which also made a connection between light and electromagnetic waves in atoms. -
G.J. Stoney
Stoney proposed that electricity was made up of nagative particles. He prposed the name electrons for the unit of electrical charge. -
Eugen Goldstein
Goldstein helped contribute to the discovery of the proton. -
Henri Becquerel
Becquerel discovered that there are spontaneous emissions of radiation from the nucleus . There are three types of radiation being emitted- positive, negative and neutral. -
JJ Thomson
Thomson discovered the electrons in atoms. He produced the 'raisin cake' model which showed that the electrons all have the same mass and charge. He proved Democritus' theory wrong- atoms are not invisible but ratehr made up of small components. -
Hantaro Nagaoka
Nagaoka thought that Thomson's model of the atom was incorrect so he created his own model. His model resembled Saturn with its rings of electrons surrounding the sphere centre. This model was later proven to be inaccurate. -
Robert Millikan and Harvey Fletcher
Millikan experimented using oil to determine the charge of an electron. -
Ernest Rutherford
Rutherford created the first model of the atom that had a nucleus. He discovered that the atom has a poistively charged nucleus which is small but has a large mass. In his model, negatively charged particles surround the atom. -
Niels Bohr
Bohr proposed an explanation for the fact that atoms with moving particles do not collapse . He discovered that electrons with the same energy move in the same energy level. -
Federick Soddy
Soddy came up with the concept of isotopes. He discovered that some elements have different forms with different atomic weights. -
Louis De Brogile
Louis De Brogile discovered that small, moving particles have a wave nature. Each moving partticle has both particle and wave properties just like light. This was confirmed by Davisson and GP Thompson. -
Erwin Schrodinger
Erwin Schrodinger created a wave mechanical model where moving electrons formed a three dimensional wave that surrounds the nucleus. -
Werner Heisenberg
Heisenberg thought that it was impossible to know the position and velocity of an electron at the same time. -
Max Born
Max Born edited Schrodingers quantum mechanics equation. This helped scientists develop the model of the atom with a nucleus surrounded by electrons at different locations when they are in different energy states. -
James Chaswick
Chaswick discovered the neutral particles in the nucleus. He called them neutrons. -
Murray Gell-Mann and George Zweig
Murray Gell-Mann discovered that all the components of an atom are held together by quarks. Both proposed the idea of quarks and then proceded to test for electrical charges in atoms. -
References
https://atomictimeline.net https://courses.lumenlearning.com/trident-boundless-chemistry/chapter/history-of-atomic-structure/ https://www.slideshare.net/mobile/JeromeJerome1/4-the-discovery-of-the-structure-of-the-atom https://i1.wp.com/www.compoundchem.com/wp-content/uploads/2016/10/The-History-of-the-Atom-–-Theories-and-Models.png?ssl=1 https://www.preceden.com/timelines/164909-timeline-of-the-evolution-of-the-atomic-theory -
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