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400 BCE
Democritus
Democritus was significant in developing the atomic theory. He came up with the idea that material bodies are all made up of extremely small atoms. Works Cited:
https://www.britannica.com/biography/Democritus -
330 BCE
Aristotle
Aristotle didn't believe in atomic theory, he however believed that all matter was made of Earth, Fire, Water, Air. Works Cited:
https://historyofatomictheory.weebly.com/aristotle.html#:~:text=He%20did%20not%20believe%20in,these%20four%20elements%20of%20matter. -
Antoine Lavosier
Lavoisier discovered oxygen in 1774 and helped develop the modern organization of the periodic table with his categorizations based on properties. He also found that mass is not lost during a chemical change which defined the law of conservation. Works Cited:
https://study.com/academy/lesson/antoine-lavoisier-atomic-theory-contribution.html#:~:text=In%20his%20book%20Elementary%20Treatise,was%20conserved%20during%20chemical%20changes. -
John Dalton
John Dalton stated that elements are made up of atoms, all atoms of the same element are the same but each element has its own kind of atom. He also claimed that atoms cannot be created or destroyed and compound elements are formed when atoms of different elements come together in simple ratios. Works Cited:
https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095658664#:~:text=A%20theory%20of%20chemical%20combination,neither%20be%20created%20nor%20destroyed. -
Dalton's model
John Dalton believed that atoms were indivisible and indestructible. This was later proven false as atoms are made out of electrons and a nucleus. Works Cited:
https://www.britannica.com/video/153020/John-Dalton-development-atomic-theory -
Michael Faraday
Faraday made the first compounds of carbon and chlorine. He made them by substituting chlorine for hydrogen in ethylene. Works Cited:
https://www.britannica.com/biography/Michael-Faraday -
Dmitri Mendeleev
Mendeleev arranged the elements in the periodic table in order of increasing atomic weight. Works Cited:
https://www.britannica.com/biography/Dmitri-Mendeleev/Other-scientific-achievements -
J.J. Thomson
Thomson discovered the electron using a high-vacuum cathode-ray tube. He thought the deflection of the rays by electronically charged plates and magnets was evidence for electrons. Works Cited:
https://www.sciencehistory.org/education/scientific-biographies/joseph-john-j-j-thomson/#:~:text=In%201897%20Thomson%20discovered%20the,invention%20of%20the%20mass%20spectrograph. -
Max Planck
Plank contributed to the atomic theory by discovering the quantum of action which made a foundation for quantum theory. Works Cited:
https://www.britannica.com/biography/Max-Planck -
Thomson's model (Plum Pudding Model)
Thomson's model shows an atom that has a positively charged space and electrons inside the space. It was given the name "Plum Pudding Model" because the positive space and electrons were like pudding with plums inside. Works Cited: https://kids.kiddle.co/Plum_pudding_model -
Robert A. Millikan
Milikan used his oil-drop experiment to determine the fundamental charge of an electron. Works Cited:
https://www.britannica.com/biography/Robert-Millikan -
Rutherford's model
In Rutherford's model, the nucleus contains protons and neutrons while the electrons orbit the nucleus. The electrons orbiting the nucleus give off electromagnetic radiation. This is wrong though because the electrons would lose energy and fall into the nucleus. Works Cited: https://www.britannica.com/science/Rutherford-model -
Ernest Rutherford
Rutherford discovered that atoms are mostly empty space the majority of their mass is in the nucleus. He also found alpha and beta particle radiation out of uranium. Works Cited:
https://www.britannica.com/biography/Ernest-Rutherford/McGill-University https://www.primaryconnections.org.au/themes/custom/connections/assets/SBR/data/Chem/sub/atom2/atom2.htm#:~:text=In%201911%2C%20Rutherford%20described%20the,planets%20revolving%20around%20the%20Sun. -
Bohr's model
Bohr's model, a refinement of Rutherford's model, depicts electrons traveling around the nucleus in fixed paths. Electrons in this model don't radiate electromagnetic radiation as they orbit the nucleus. The amount of electrons on each orbit corresponds to its energy level. Works Cited: https://www.britannica.com/science/shell-atomic-model -
Erwin Schrödinger
Erwin Schrödinger contributed to the atomic theory by showing the quantization of the hydrogen atom's energy levels in the Bohr model could be calculated from his equation. His equation called the Schrödinger equation, describes the evolution of wave functions in a quantum mechanical system. Works Cited:
https://www.britannica.com/biography/Erwin-Schrodinger -
James Chadwick
James Chadwick discovered the neutron by placing polonium in a vacuum-sealed box. This caused alpha particles to radiate through a piece of beryllium which resulted in unknown radiation coming out. Chadwick believed the radiation to be neutrons. Works Cited:
https://study.com/academy/lesson/james-chadwick-biography-atomic-theory.html#:~:text=James%20Chadwick's%20contribution%20to%20the,neutron%20and%20measure%20its%20mass.