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450
Democritus (430 B.C.)
Democritus proposed that matter is made of tiny particles called atoms. There was no previous model to base his off of, so he is considered the first to come up with an atomic theory.
He believed that he could break something in half so many times until a tiny, invisible, and indestructible particle is left. He named this the atom, as atom means in Greek, invisible or uncuttable.
Chemistry Project : The History Of The Atom." Chemistry Project : The History Of The Atom. N.p., n.d. Web. 26 -
450
Aristotle (384-322 B.C.) http://you-and-i-have-chemistry-3.blogspot.com/
Aristotle believed that the atom did not exist and, regardless of the number of times you cut something, there will always be something smaller. Instead he believed in the four elements of air, earth, water, and fire.
Aristotle did not have a method of disproving Democritus and his atomic theory. He simply had a different belief which for a long time was widely accepeted due to the fact that he taught the general Alexander the Great.
Http://ffden-2.phys.uaf.edu/211_fall2004.web.dir/Danny_D -
Period: 450 to
History of the Atom
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John Dalton "History of Atoms." History of Atoms. N.p., n.d. Web. 26 Feb. 2014. http://www.stgabriel.net/stgabriel_new/school/StudentWork/patrickandtyler/Atom%20project.html
Through performing several experiments with various chemicals, Dalton discovered that matter seemed to consist of particles (atoms). He was not able to prove why, but he knew the evidence supported his theory.
Dalton discovered his theory through his experiments with gases. He found that elements combine at the atomic level in fixed ratios. This ratio would differ in compounds due to the unique atomic weights of the elements being combined.
"Chemistry Project : The History Of The Atom." C -
J.J. Thomson DeWitt, Tyler. "Discovery of the Electron: Cathode Ray Tube Experiment - Cathode Ray Tube Experiment | Socratic, Learning Made Easier." Socratic.org. N.p., n.d. Web. 27 Feb. 2014.
Thomson was able to discover a new form of the atom by his discovery of the atom. He knew from his experiments of cathode rays that there were negatively charged particles, electrons, within atoms. But he also knew that in order to have something negative there had to be a positive charge as well, because opposites attract eachother.
Using glass tubes and positive and negative plates inside the tube, Thomson discovered that something negatively charged was present, as the rays deflected. -
Rutherford "History of Atoms." History of Atoms. N.p., n.d. Web. 26 Feb. 2014. http://en.wikipedia.org/wiki/Rutherford_model
Rutherford determined that there weren't positively charged spheres in an atom, but rather particles in an atom that were positively charged.
Using his gold foil experiment, Rutherford proved that there were positively charged particles that occasionally scattered the negatively charged alpha rays. Most of the alpha rays passed through the gold foil, but occasionally the alpha particle would deflect off of a hard substance, called a nucleus, in a different direction. -
Neils Bohr (1912-1920's) "History of Atoms." History of Atoms. N.p., n.d. Web. 26 Feb. 2014. http://en.wikipedia.org/wiki/Bohr_model
Bohr discovered that electrons travel in orbital motions that can be influenced by magnetic fields to create different orbital shapes. He also theorized that electrons could jump from a higher enery level to a lower one (and vice versa), thus creating light rays, or photons.
He came up wiith two rules. 1) Electrons can orbit only at certain allowed distances from the nucles and 2) Atoms radiate energy when an electron jumps from a higher-energy orbit to a lower one. -
Heisenburg and Schrodinger (1925-1927) "History of Atoms." History of Atoms. N.p., n.d. Web. 26 Feb. 2014. http://atomic-timeline.weebly.com/
In 1927, Schrodinger decided he would form a model of the atom with particle waves. He gave his wave the symbol psi based on the Greek symbol. In 1925 Heisenburg had a theory named matrix mechanics. He based his theory on particles whereas Schhrodinger based his on waves.
After some experiments, Heisenburg proposed his 'uncertainty principle" that stated if you were to measure the position of a particle, the uncertainty of the momentum gets larger.
