History of the Atom

1. History of the Atom By: Kelly Audria

2. Democritus – 460 BC • Democritus discovered that all matter was composed of small particles that he called atoms. They were composed of the same primary matter, the only differences between atoms are the size, weight and shape. As well as figuring out that all atoms are invisible and so small they the can’t be torn apart. http://www.livius.org/de-dh/democritus/democritus.html

3. http://fcit.usf.edu/florida/teacher/science/mod3-resources/lecture2.htmhttp://fcit.usf.edu/florida/teacher/science/mod3-resources/lecture2.htm Dalton - 1803 • Dalton is credited by most for being the first person that come up with the first atomic theory. It states that “All matter is composed of tiny, indestructible particles called atoms that are all alike and have the same atomic weight”. Dalton did experiments on different gases to find out what effect the properties of an individual gas had on the property of a mixture. He then came up with a hypothesis that the size of the particles that make up different gases must be different. Which led him to the atomic theory. http://www.hcc.mnscu.edu/chem/V.07/page_id_33296.html

4. Mendeleev - 1869 • Mendeleev became a professor and wanted a appropriate book that was on general chemistry, since there wasn’t one he wrote his own. Mendeleev created the first periodic table, letter symbols for each element. Today it is changed but his table is still some of the basic elements. http://www.bluffton.edu/~bergerd/nsc_111/science2.html

5. Eugene Goldstein - 1885 • Discovered anode rays, also known as canal rays. Positively charged particles that form when electrons are removed from gas particles in a cathode-ray tube. His worked showed what is known as a proton, discovered by Rutherford, today. http://chemed.chem.purdue.edu/genchem/history/goldstein.html

6. Henri Becquerel - 1896 • Becquerel discovered radioactivity. He experimented with uranium and other substances to find out they are radioactive. http://www.nndb.com/people/608/000072392/

7. J J. Thomson - 1897 • Thomson discovered the election with the cathode-ray tube. He also made the plum-pudding model of what and atom is made of. http://en.wikipedia.org/wiki/J._J._Thomson

8. Ernest Rutherford - 1907 • Discovered that an atoms structure is nuclear. He also used cathode rays, but he discovered the a mass and atomic number could be found. http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1908/rutherford-bio.html

9. Millikan - 1910 • Used the “falling drop method” to see that the quantity was a constant number for electrons. It was a charge carried by an electron. This showed the atomic structure of electricity. http://www.nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.html

10. Neils Bohr - 1913 • Designed a picture of an atomic structure, using quantum theory. It serves as a elucidation of both the physical and chemical properties of an element. http://www.atomicarchive.com/Bios/BohrPhoto.shtml

11. Frederick Soddy - 1913 • Soddy made a formulation with his concept of isotopes. It said that “certain elements exist in two or more forms which have different atomic weights but which are indistinguishable chemically”. There can be more than one element which would make it an isotope but you can’t tell the difference chemically. http://www.nndb.com/people/286/000099986/

12. Heisenberg - 1925 • Heisenberg made the foundation of quantum mechanics. Quantum mechanics helps describe and predict the behavior of subatomic particles. http://www.marxists.org/reference/subject/philosophy/works/ge/heisenb2.htm

13. Chadwick - 1932 • Chadwick discovered the neutron, an uncharged particle in the nucleus. Used this to made the fission of uranium 235, which is used for atomic bombs. http://www.aps.org/publications/apsnews/200705/physicshistory.cfm