History of the Atom Timeline Project

1. History of the Atom Timeline Project By: Rachel Kohler http://csep10.phys.utk.edu/astr162/lect/light/bohr.html

2. Democritus460 BC Democritus developed the idea of atoms, he created this theory by pounding up materials in his pestle and monitor until he eventually had reduced the materials into smaller and smaller parts. He had called these particles Atoma, singular, or Atomas, two or more, which is a Greek word for indivisible. http://www.stellmanngfs.glogster.com http://www-groups.dcs.stand.ac.uk/~history/Biographies/Democritus.html http://www.quotecollection.com/author/democritus/

3. John Dalton1803 John Dalton’s theory suggested numerous ideas such as all matter is made up of atoms, which are individual and indestructible, atoms that are from the same element are identical, two or more atoms form a compound, and the rearrangement of atoms is a known as a chemical reaction. Dalton’s atomic theory was based on the principle that all atoms could be distinguished by their weight. http://www.rsc.org/chemsoc/timeline//pages/1803.html http://www.iun.edu/~cpanhd/C101webnotes/composition/dalton.html http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/the-path-to-the-periodic-table/dalton.aspx

4. Mendeleev1869 Mendeleev’s greatest and most well known achievement was the periodic table. He was able to organize and arrange all of the 63 elements, not only by their own atomic weights but also by the groups that had similar properties. He also was so intelligent that he made a prediction that one day a new element would be discovered, and he was eventually right. http://www.rsc.org/chemsoc/timeline//pages/1869.html http://www.bluffton.edu/~bergerd/nsc_111/science2.html

5. Eugene Goldstein1885 Eugene had studied in X-rays and tube energy rays extending from a negative electrode. When they had hit the glass walls of the tubes, they had produced fluorescence. Eugene had used his finds to find that this particle, the proton, was positive and this it is equal to and opposite of the electron. http://www.picses.eu http://edu.glogster.com/media/5/25/53/52/25535237.gif

6. Henri Becquerel1896 Henri Becquerel discovered radioactivity, then he had decided to examine it to see if there was a possible connection between X-rays and naturally occurring phosphorescence. Henri used uranium salts, which phosphoresce with the contact to light, when the salts had been put next to a photographic plate that was enclosed with opaque paper. The result was that the plate was fogged. He later discovered that they rays released by uranium, which cause gases to ionize, were repelled by electric or magnetic fields. http://www.uwec.edu http://www.nobelprize.org/nobel_prizes/physics/laureates/1903/becquerel-bio.html

7. J.J. Thomson1897 Thompson was examining cathode rays when he then made his major discovery of the electron. He was using a highly evacuated discharge tube when he then calculated the ratio of the electric charge to the mass of the cathode ray by using the velocity and the deflection of the beam that was calculated. In spite of the gas that was used in the tube and the metal of the cathode, this experiment was constant. Also, Thompson invented the plum pudding method, which is the way he described how he thought the electrons and the nucleus looked. http://www.rsc.org/chemsoc/timeline//pages/1897.html http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/thomson.aspxing

8. Ernest Rutherford1907 Ernest Rutherford’s famous discovery of the nucleus was made possible by his well known experiment, which required him to fire radioactive particles through a think piece of gold. Ernest found that even though most of the particles had penetrated through the gold, some were still deflected. This made him conclude that most atoms were made of space, but also that in the middle of each atom is a nucleus. http://www.rsc.org/chemsoc/timeline//pages/1911.html http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html

9. Robert Andrews Millikan1910 Robert Millikan used the falling drop method to figure out the charge that was carried by an electron. Millikan had demonstrated the atomic structure of electricity to establish that this, for all electrons was a constant. http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html

10. Niels Bohr1913 Bohr revaluated Ernest Rutherford’s theory of the nucleus that said each atom had a small, but thick nucleus that was bordered by a cloud of electrons. Neils Bohr then came up with the theory that the electrons that surrounded the nucleus were at fixed distances from the nucleus and at set levels of energy, if the atom absorbed energy or radiated energy the electron would move either closer or farther from the nucleus. http://www.universetoday.com/42841/bohr-atom/ http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio .html

11. Frederick Soddy1913 Frederick Soddy came up with the idea of isotopes, which he had declared that certain elements can exist in two or even more forms. The elements may have diverse atomic weights although they are impossible to chemically differentiate. http://www.nndb.com/people/286/000099986/ http://www.nndb.com/people/286/000099986/

12. Heisenberg1925 Werner Heisenberg had created matrix mechanics in 1925, which was the first version of quantum mechanics. Werner had all of his attention placed on a set of quantized probability amplitudes, which formed a non-commutative algebra. http://www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html http://www.nobelprize.org/nobel_prizes/physics/laureates/1932/heisenberg-bio.html

13. Chadwick1932 Chadwick made a discovery in the domain of nuclear science he then showed that neutrons exist. Neutrons are basic particles that have no electrical charge. Helium nuclei in comparison with the alpha rays that are charged, so consequently they repel by the considerable electrical forces that are in the nuclei of heavy atoms. http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html http://www.nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html