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400
Democritus
400BC
Democritus was the first to propose that all matter was made up of atoms.
Atom meant "Indivisible in Greek"
-Based on the Idea that atom could not be divided any further.
Unfortunately, at this time Democritus could not test his theories. -
John Dalton's Atomic Theory
Dalton's new atomic theory was based on 5 individual hypotheses, 2 of which turned out to be false (2 and 3).
1. All matter is made up of Atoms.
2. All atoms contained in an element have the same properties. All atoms in seperate elements have different properties.
3. You cannot divide, create, or destroy an atom.
4. Atoms with differing elements can form chemicals when their combination results in whole-number ratios.
5. Atoms will combine, seperate, and rearrange in chemical reactions. Notes -
JJ Thomson Discovers Electrons
"Discovered " Electrons
Eperiments with CRT (Cathode Ray Tube).
Credited with discovering the first subatomic particle and named it the electron. http://www.nobelprize.org/nobel_prizes/physics/laureates/1906/thomson-facts.html (Accessed 3/30/14)
Class Notes -
JJ Thomson's Model
JJ Thomson's Atomic Model Thomson Plum Pudding Model states that the atom is full of electrons that are surrounded by protons to balance the negative charges. Class Notes -
Ernest Rutherford's Atomic Theory and Discovery of Protons
Disproved the Thomson Model with his Gold Foil Experiment.
-Rutherford fired Alpha particles at Gold Foil expecting the particles to go right through, based on Thomson's Model. While some did go through the foil, many bounced off the foil and spread.
Rutherford says that based on his experiment, an atom must have a nucleus, where all the positive charge and mass are located orbited by electrons. Class Notes
"The Physical Universe" Pg. 290-291
"The Physical Universe" Pg. 290-291 -
Ernest Rutherford's Atomic Model
Rutherford says that based on his experiment, an atom must have a nucleus, where all the positive charge and mass are located orbited by electrons. "The Physical Universe" Pg. 290-291 -
Niels Bohr's Atomic Theory
Bohr suggests that atomic electrons only have certain particular energies and that these energies are based on what orbit around the atom they fall in.
Electrons in the orbit closest to the atom have the lowest energy, and the further out the orbit is, the more energy the electron has. "The Physical Universe" Pg. 341-45 -
Niels Bohr's Atomic Model
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The Heisenberg Uncertainty Principle
Heisenberg discovered that imprecisions always occured when trying to measure both the position and momentum of a particle. This translates to atoms in that it is almost impossible to measure the position of an electrons' orbit around the nucleus of an atom. http://www.aip.org/history/heisenberg/p08.htm (Accessed 3/30/14) -
James Chadwick Discovers the Neutron
Chadwick tried to rationalize the atomic number of an element being higher than it's combined number of electrons and protons. He discoverd the Neutron after using experiments conducted by Frederic and Irene Curie. He changed these experiments used to detect particle rediation and started looking for his neutral particle. He was successful in discovering the neutron. http://www.pbs.org/wgbh/aso/databank/entries/dp32ne.html (Accessed 3/30/14) -
Gellman and Zweig "Invent" Quarks
Seeking a deeper understanding of what makes up an atom, Gellman and Zweig invented a naming system called Quarks with 3 types: up, down, or strange. We now have 3 more: top, bottom, charm making a total of 6.
A quark is, simply put, a small particle that nucleons can be divided into. http://www.slac.stanford.edu/cgi-wrap/getdoc/slac-pub-5724.pdf (Accessed 3/30/14)
