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500 BCE
The Alchemists
The Alchemists started to understand the composition of objects. https://prezi.com/t50cihtay12m/alchemy-and-its-contributions-to-the-atomic-theory/ -
430 BCE
Democritus
Democritus believed atoms were uniform, indestructible, and moved through space until stopped. He also named atoms. https://www.britannica.com/science/atom/Development-of-atomic-theory -
5 BCE
Plato
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Robert Boyle
Robert Boyle helped develop the definition of an element. https://sites.google.com/site/robertboyletheskepticalchemist/atomic-theory-contribution -
Antoine Lavoisier
Antoine Lavoisier found mass is conserved in chemical reactions. http://chemed.chem.purdue.edu/genchem/history/lavoisier.html -
Billiard Ball Model
The Billiard Ball Model shows atoms as compact, hard spheres, so John Dalton showed these atoms as billiard balls. https://flexbooks.ck12.org/cbook/ck-12-middle-school-physical-science-flexbook-2.0/section/3.12/primary/lesson/daltons-atomic-theory-ms-ps/ -
John Dalton
John Dalton proposed that everything was composed of atoms, and that atoms varied in size and mass. He also believed all the atoms of an element were/are identical. https://courses.lumenlearning.com/introchem/chapter/john-dalton-and-atomic-theory/#:~:text=Dalton's%20atomic%20theory%20proposed%20that,of%20differing%20size%20and%20mass. -
Amedeo Avogadro
Amedeo Avogadro hypothesized that equal volumes of different gases contain an equal number of molecules. https://www.sciencehistory.org/historical-profile/amedeo-avogadro#:~:text=In%201811%20Avogadro%20hypothesized%20that,contain%20equal%20numbers%20of%20molecules.&text=According%20to%20Avogadro%2C%20the%20molecule,course%20of%20forming%20water%20vapor. -
Dmitri Mendeleev
Dmitri Mendeleev invented the periodic table of elements by categorizing them by their atomic weights. https://www.newscientist.com/people/dmitri-mendeleev/ -
Pierre and Marie Curie
Pierre and Marie Curie discoverd radiation, and 2 new elements: radium and polonium. https://www.atomicheritage.org/profile/marie-curie -
JJ Thompson
JJ Thompson found all atoms contain tiny negative charged subatomic particles or electrons https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/history-of-atomic-structure/a/discovery-of-the-electron-and-nucleus#:~:text=Summary-,J.J.,positively%2Dcharged%20%22soup.%22 -
Plum Pudding Model
The Plum Pudding Model shows the atomic structure of atoms. It shows electrons surrounded by a positive charge. It was proposed by J.J. Thompson. https://www.electrical4u.com/thomsons-plum-pudding-model/ -
Albert Einstein
Albert Einstein mathematically proved the existence of atoms. https://www.ans.org/news/article-969/albert-einstein-and-the-most-elemental-atomic-theory/#:~:text=Einstein%20also%20in%201905%20mathematically,use%20of%20statistics%20and%20probability.&text=Atomic%20theory%20says%20that%20any,always%20in%20random%2C%20ceaseless%20motion. -
Robert Millikan
Robert Millikan discovered there is a fundamental electric charge. https://courses.lumenlearning.com/chemistryformajors/chapter/evolution-of-atomic-theory/#:~:text=Millikan%20discovered%20that%20there%20is,the%20nucleus%20are%20called%20protons. -
Ernest Rutherford
Ernest Rutherford found the atom is mostly empty space, and the nucleus is positively charged. https://www.britannica.com/biography/Ernest-Rutherford -
Neils Bohr
Neils Bohr believed electrons moved around the nucleus in "prescribed" orbtis. He created the solar system model. https://www.nobelprize.org/prizes/physics/1922/bohr/biographical/ -
Solar System Model
The Solar System Model shows an atom with a nucleus (the sun) with electrons (planets) orbiting around it. Niels Bohr came up with the model. https://www.osti.gov/opennet/manhattan-project-history/Events/1890s-1939/exploring.htm -
Henry G. J. Mosely
Henry G. J. Mosely created the atomic number, which is the number of positive charges in the nucleus of an atom. https://www.britannica.com/biography/Henry-Moseley -
Erwin Schrödinger
Erwin Schrödinger used math equations to find the likelihood of electrons being in a certain position based on previous locations. (Quantum Mechanical Model) http://www.abcte.org/files/previews/chemistry/s1_p6.html -
Electron Cloud Model
The Electron Cloud Model shows an atom with a nucleus surrounded by fast moving electrons. It shows us we cannot place the exact spot of an electron at an exact time. It was developed by Erwin Shrödinger. https://www.nuclear-power.com/nuclear-power/reactor-physics/atomic-nuclear-physics/fundamental-particles/what-is-electron-properties-of-electron/electron-cloud/#:~:text=Electron%20cloud%20model%20is%20a,to%20be%20in%20specific%20areas. -
Werner Heisenberg
Werner Heisenberg discovered the uncertainty principle, which proposes a particles position and momentum cannot be exactly known. https://www.britannica.com/biography/Werner-Heisenberg -
James Chadwich
James Chadwich found that atoms consist of neutrons. This meant that there were 3 parts of an atom: protons, neutrons, and electrons. http://www.abcte.org/files/previews/chemistry/s1_p6.html
