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The Alchemists helped break down the elements into Atoms and now come up with names for different types of matter and substances that we have on the periodic table now. https://www.bing.com/search?q=When%20did%20the%20alchemist%20develop%20the%20atom&qs=n&form=QBRE&sp=-1&pq=when%20did%20the%20alchemist%20develop%20the%20atom&sc=0-39&sk=&cvid=7B691F5850E54BE3A84ECE65577F9D57
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He theorized that atoms always were in constant motion and collided together and e realized that they could differ in size ad speed and o stick together. https://www.bing.com/search?q=when+did+democritus+develop+the+atomic+theory&qs=SC&pq=when+did+democrit+develop+the+atom&sc=1-34&cvid=635961A7844249429AE232CEA0BE82C3&FORM=QBRE&sp=1
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He introduced the atomic theory in which geometric forms served as atoms and could be broke down into triangles and could form different elements. https://www.bing.com/search?q=when%20did%20plato%20develop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=1_2&sp=-1&pq=when%20did%20plato%20develop%20the%20atomic%20theory&sc=1-40&sk=&cvid=0A9F9EB69F854BAC959042537A43AF8B
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The only thing he did that is still true today is that their are elements everything else was False.
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Robert Boyle made a Law That states if the volume of gas is decreased the pressure increases proportionally. Understanding that his results could be true if all gasses were made of tiny Atoms. https://www.bing.com/search?q=when%20did%20robert%20boyledevelop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=1_2&sp=-1&pq=when%20did%20robert%20boyledevelop%20the%20atomic%20theory&sc=1-46&sk=&cvid=DB6F4BCC6CCD4F5FB931B1E330FFC45B
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He discovered that no matter the total mass or the destruct ants the chemical mass is always the same and it led to the law of conversion to mass. https://www.bing.com/search?q=when+did+lavoisier+develop+the+atomic+theory&FORM=AWRE
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He theorized that all atoms were compounds and composed of combinations in defined ratios. And resulted in the arrangement of reacting atoms. https://www.bing.com/search?q=when%20did%20John%20Dalton%20develop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=1_2&sp=-1&pq=when%20did%20john%20dalton%20develop%20the%20atomic%20theory&sc=1-46&sk=&cvid=0E4054E6AF2646DC8D4B41DC9EB94D62
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He made great contributions to the atom by creating the first periodic table of elements. He concluded that there are still more elements to be discovered that are to be added to the periodic table. https://www.bing.com/search?q=what+di+Dmitri+mendeleev+do+to+help+develop+the+atom&cvid=fc779fef58264b10b0093f512f3a8507&FORM=ANNTA9&DAF0=1&PC=U531
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They helped show hat atoms can be radioactive and have spontaneous penetrating rays by certain atoms. https://www.bing.com/search?q=when%20did%20the%20curies%20develop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=1_2&sp=-1&pq=when%20did%20the%20curie%20develop%20the%20atomic%20theory&sc=1-44&sk=&cvid=67FEE18ED13248CEB54A9A19ABAF0D05
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He suggested a module model of the atom as a sphere of positive matter in which electrons are positioned by electrostatic forces. Link https://www.bing.com/search?q=J.J%20Thomson%20how%20did%20he%20help%20develop%20the%20model%20&qs=n&form=QBRE&msbsrank=0_1&sp=-1&ghc=1&pq=j.j%20thomson%20how%20did%20he%20help%20develop%20the%20model%20&sc=0-46&sk=&cvid=FFA4F3C1F0A443B9B9C87419155D299C
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He developed the photoelectric effect so when a light energy strikes atoms in the metal the "quanta force releases electrons" https://www.bing.com/search?q=when%20did%20albert%20einstein%20develop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=0_1&sp=-1&pq=when%20did%20albert%20einstein%20develop%20the%20atomic%20theory&sc=0-50&sk=&cvid=6CAF3FC2385E44988EE829C9D6AE1629
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Robert Millikan determined the unit charge of the electron with his oil drop experiment at the University of Chicago.
Link https://www.bing.com/search?q=How+did+robert+milikan+help+develope+the+atom&cvid=fb261897b03044b5b8c1e12a616c1dd1&FORM=ANNTA9&DAF0=1&PC=U531 -
He is the one that developed the nuclear structure of the atoms and he found that alpha particles violently reflect when they hit into gas atoms. https://www.bing.com/search?q=when%20did%20earnest%20rutherford%20develop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=0_1&sp=-1&pq=when%20did%20earnest%20rutherfor%20develop%20the%20atomic%20theory&sc=0-52&sk=&cvid=05B0AEF943DE465EB5450FC24AFB04B4
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He helped the atoms development by finding out how the energy is used and how much in certain atoms wavelengths. https://www.bing.com/search?q=when%20did%20neils%20bohrdevelop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=1_2&sp=-1&pq=when%20did%20neils%20bohrdevelop%20the%20atomic%20theory&sc=1-44&sk=&cvid=29D59033A101427384202F3C1A2CB736
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He created the atomic number for the periodic table which made it much easier to understand that atomic mass.
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He formulated quantum mechanics in terms of matrices and in discovering the uncertainty principle of atoms. https://www.bing.com/search?q=when%20did%20werener%20heisenbergrdevelop%20the%20atomic%20theory&qs=n&form=QBRE&msbsrank=0_1&sp=-1&pq=when%20did%20werener%20heisenbergrdevelop%20the%20atomic%20theory&sc=0-53&sk=&cvid=2AB78E1D1F1641C4A2BD58AC8DED5E28
