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Democritus was an ancient Greek philosopher. He discovered atomic theory, the universe, and atomism.

Around 400 BC Democitrus discovered the atomic theory. He was experimenting with rocks and knew that everytime you split the rock in half the properties are still the same and still continue till to the piece looked invisible because it was so small. He called matter or pieces of matter “atoms” and theorized that matter differed in shape and size.

Also around the same time he discovered the atomic theory. Democritus also helped discover/philosophize atomism. Atomism was where the universe is composed of “mintute particles”. Minute particles are particles that are tiny in size and cannot be seen with the human eye.

CITATIONS:

https://www.britannica.com/topic/atomism

https://www.collinsdictionary.com/us/dictionary/english/minute-particles

http://www.abcte.org/files/previews/chemistry/s1_p1.html

https://www.britannica.com/biography/Democritus

https://rinconeducativo.org/en/recursos-educativos/modelo-atomico-de-democrito-400-ac/

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This model was Democritu's atomic model for an atom. Democritus belived atoms were solid, hard and werent able to be destroyed nor created but moved in an empty space.

CITATIONS:

https://www.sutori.com/en/story/the-history-of-atoms

https://www.britannica.com/science/atom/Development-of-atomic-theory

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Aristotle was a Greek Philosopher and polymath. He claimed that four elements were not made of atoms but forms of matter. His philosophy “change was not explained by a rearrangement of atoms but by the transformation of matter the potential of its actuality”. Aristotle made this philosophy/discovery around 300 BC. He used fresh and salt war in his experiments but did not go into depth. Aristotle's discoveries led to the field of formal logical as well and contibuted to the atomic theory.

CITATIONS:

https://taylalawson.wordpress.com/aristotle/

https://www.britannica.com/biography/Aristotle

https://www.cambridge.org/core/journals//

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His model showed that different substances were made of small amounts of matter and four elements; fire, air, earth and water.

CITATIONS:

http://www.chemistryland.com/CHM130S/05-EarlyAtom/EarlyAtom.html

https://historyofatomictheory.weebly.com/aristotle

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John Dalton was an English chemist and physicist. Dalton’s atomic theory was the most impactful to chemistry. He proposed his atomic theory in 1804. Dalton's contribution to the Atomic theory contained that elements have atoms/small particles, all atoms are the same, atoms cant be destroyed/created, compound elements are created through different elements, and that atoms vary in size/mass. He used oxygen mixed with 1-2 volumes of nitric oxide above water as for his evidence for his atomic theory.

CITATIONS:

https://www.britannica.com/biography/John-Dalton/Atomic-theory

https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/

https://pubmed.ncbi.nlm.nih.gov/18175369/

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John Dalton's atomic model showed an atom and how it was indestructable and is invisible. But the weight of the atom fairly depends of it's elements and adding different compounds/elements will change its weight. He called his atomic model the "Billiard Ball Model".

CITATIONS:

https://time.graphics/period/1442788

https://brilliant.org/wiki/daltons-atomic-model/

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J.J. Thomson was an British physicist. On April 30, 1897 Thomson discovered that atoms are made up of smaller components and electrons. Also, he created a structure of the atom. Thomsons discovery led to the creation of mass spectrogtaph (a technique to measure mass -> charge ratio of ions). To prove his discovery he put opposite charged electric plates around a cathode ray and the cathode ray deflected from negative to positive which showed the cathoderay was made of negative atoms/particles.

CITATIONS:

https://www.khanacademy.org/science/chemistry/electronic-structure-of-atoms/

https://sciencehistory.org/education/scientific-biographies/joseph-john-j-j-thomson/

https://www.broadinstitute.org/technology-areas/what-mass-spectrometry

https://www.nobelprize.org/prizes/physics/1906/thomson/biographical/

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J.J. Thomsons atomic model was known as the Plum Pudding model. His model showed negative charged parts of an atom. This model did soon get abandonded due to Rutherfords future atomic model.

CITATION:

https://www.britannica.com/science/Thomson-atomic-model

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Ernest Rutherford was a New Zealand physicist. Rutherford's major discoveries included that there are 2 types of radiation, atoms consist of an empty space & alpha and beta particles, posulated the nuclear structure of an atom, etc. His discoveries created many other discoveries in radioactivity and nuclear physics and made his discovery in 1911. Rutherford used a scattering technique/experiment; Rutherford used a gold foil and shot a beam of alpha particles at the gold foil and some particles were deflected off of it.

CITATIONS:

https://www.fnal.gov/pub/inquiring/timeline

https://kids.britannica.com/students/assembly/view/

https://www.britannica.com/biography/Ernest-Rutherford

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Ernest Rutherfords atomic model, also known as the Rutherford model showed large amiunts of charge in a small volumee containing the atoms mass showing the nucleus.

CITATIONS:

https://web.archive.org/web/20060502124241/http://www.rwc.uc.edu/koehler/biophys/7a.html

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Niel Bohr was a Danish physicist. Bohr showed evidence in his claim that electrons were limited to certain orbits around the nucleus. He created and presented a model of an atom that showed an electron was able to use certain orbits around a nucleus and was the first to use quantum theory. Bohr made his discovery in 1913 and made a proposal. His discoveries made major contributions to atomic theory.

CITATIONS:

https://ahf.nuclearmuseum.org/ahf/profile/niels-bohr/

https://www.britannica.com/biography/Niels-Bohr

https://www.nobelprize.org/prizes/physics/1922/bohr/facts/

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Niel Bohr made many models on different elements known as the Bohr Models. The model shown is a Nitrogen atom and it shows that a nucleus exists and has orbiting atoms that are lower and higher.

CITATIONS:

https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/

https://www.britannica.com/science/Bohr-model

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Erwin Schrodinger was an Austrian-Irish physicist. He contributed to quantum physics; wave mechanics and the unified field theory. One of Schrodinger’s major discoveries was his wave equation due to his not agreeing with Bohr’s orbit theory. Known as the Schrodinger cat; He experimented with a cat with a small amount of radioactive substances and after an hour of it decaying and not decaying, he made his discovery in 1926.

CITATIONS:

https://history.aip.org/phn/11810008.html
https://www.britannica.com/biography/Erwin-Schrodinger

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Schrodinger's model shows electrons do not follow orbits but are found in orbitals. Also, his model is based on the quantum mechanical and wave nature of electrons.

https://scienceready.com.au/pages/schrodingers-contributions-to-the-atomic-model#:~:text=In%20Schr%C3%B6dinger's%20model%2C%20electrons%20do,in%20equations%20called%20wave%20functions.

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Albert Einstein was an theoretical physicist. Einstein had many major discoveries, some examples are the Theory of Relativly and mathematically proved the existence of atoms, both discovered in 1905. He largely contributed to atomic physics and atomic theory and revolutionized sciences through statistics & probability. For the Theory of Relativly he used the idea of accderlation to mimic gravity to an idea that inertia is a gravtiaional effect. Einstein also Mathematically proved the existance of atoms by the “-movement of molecules in a liquid caused by the Brownian motion”. einstein’s discoveries led to modern-day inventions; most things we use in everyday life.

CITATIONS: https://www.ans.org/news/article-969/albert-einstein-and-the-most-elemental-atomic-theory/

https://www.usatoday.com/story/news/world/2023/05/31/what-did-albert-einstein-invent/

https://www.ck12.org/flexi/physical-science/einsteins-concept-of-gravity/

https://sites.pitt.edu/~jdnorton/teaching/

https://www.britannica.com/biography/Albert-Einstein

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Albert Einsteins atomic model shows the Special Theory of Relativity. Einstein shows how the movement of molecules can cause the Brownian motion.

https://time.graphics/line/15311

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Werner Heisenberg was a German theoretical physicist. He contributed to the atomic theory majorly. Heisenberg made his discoveries in 1925; formulated quantum mechanics and discovered the uncertainty principle. He experimented by trying to measure the position of an electron with a type of microscope and the high energy photon illuminated the electron and changed its speed/momentum.

CITATIONS:

https://www.britannica.com/biography/Werner-Heisenberg

https://www.aps.org/publications/apsnews/

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Heisenberg's atomic model was inspired by Bohr's model but slowly developed as he Matrix Formulation and showed how neutrons and protons can be orbitted and together.

https://study.com/learn/lesson/werner-heisenberg-theories.html