History of the Atom

Democritus 460 B.C.

Democritus hypothesized that atoms were undestructable. He also thought they were indivisable. His theories were not based on scientific method.

http://www.wikigallery.org/wiki/painting_318696/Charles-Antoine-Coypel/The-Cheerful-Democritus

Dalton 1803

Dalton used experimental observations to come up with a 4-part scientific theory. The first part is that all elements are composed of tiny individual particles called “atoms”. Part 2 is that atoms of the same element are identical. The atoms of any one element are different from those of any other element. Part 3 is atoms of different elements can chemically combine in whole number ratios. Part 4 is that chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.http://www.1902encyclopedia.com/

C/CHE/chemistry-014.html

Mendeleev 1869

Mendeleev formulated a periodic table similar to the one we use today. Elements were grouped according to recurring trends in their properties.

http://chemistry.about.com/od/famouschemists/p/mendeleevbio.htm

http://www.bluffton.edu/~bergerd/nsc_111/science2.html

Eugene Goldstein 1885

Goldstein concluded that cathode-ray tubes with a perforated cathode emit a glow from the end of the tube near the cathode. Goldstein concluded that in addition to the electrons there is another ray that travels in the opposite direction, from the anode toward the cathode.

http://chemed.chem.purdue.edu/genchem/history/goldstein.html

http://www.dipity.com/montelt292/History-of-Atomic-Theory/

Henri Becquerel 1896

Becquerel was a French physicist who discovered radioactivity through his investigations of uranium and other substances. In 1903 he shared the Nobel Prize for Physics with Pierre and Marie Curie.

http://www.britannica.com/EBchecked/topic/58020/Henri-Becquerelhttp://www.nndb.com/people/608/000072392/

J.J. Thomson 1897

Thomsom played with Cathode ray tube experiments just like Goldstein. He measured charge to mass ratio of negatively charged particles for different gases. He also created the “raisian in the dough” model of the atom.

http://www.chemheritage.org/discover/online-resources/chemistry-in-history/themes/atomic-and-nuclear-structure/thomson.aspx

Ernest Rutherford 1907

Rutherfold’s gold foil experiment disproved Thomson’s atomic model. He showed that the atom is mostly just empty space. Most of the mass is contained in a compact, has a positively charged center and a nucleus.

http://en.wikipedia.org/wiki/Ernest_Rutherford

Millikan 1910

Millikan experimentally determined that the charge was carried by the electron. He used mass/ charge ratio created by Thomson. He used this for calculating the mass of an electron.

http://www.xtimeline.com/evt/view.aspx?id=71291

Frederick Soddy 1913

Soddy proposed that the same elements exist in different forms, with nuclei having the same number of protons but different numbers of neutrons. His theory of isotopes explained that different elements can be chemically indistinguishable but have different atomic weights and characteristics.

http://www.nndb.com/people/286/000099986/

http://theanatomyofmelancholy.tumblr.com/post/1054790261/radiochemist-frederick-soddy-born-september-2

Neils Bohr 1913

Bohr was the first to apply the quantum concept. The concept restricted the energy of a system to certain discrete values, to the problem of atomic and molecular structure. For this work, he received the Nobel Prize for Physics in 1922.

http://www.britannica.com/EBchecked/topic/71670/Niels-Bohr

http://www.nobelprize.org/nobel_prizes/physics/laureates/1922/bohr-bio.html

Heisenberg 1925

Heisenberg was a German physicist and philosopher who discovered a way to formulate quantum mechanics in terms of matrices. For this discovery, he was awarded the Nobel Prize for Physics for 1932. http://www.britannica.com/EBchecked/

topic/259761/Werner-Heisenberghttp://en.wikipedia.org/wiki/Werner_Heisenberg

Chadwick 1932

Chadwick discovered the neutron in 1932. His discovery formed the base for the investigation of the tougher questions of nuclear physics: the nature of the nucleus and its forces. In 1935, he received the Nobel Prize for Physics.

http://www.light-science.com/chadwick.html

http://scientistsinformation.blogspot.com/2011/03/sir-james-chadwick-1891-1974.html