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TIMELINE OF ATOMIC STRUCTURE

Greekera

Democritus "by convention bitter, by convention sweet, but in reality atoms and void"

1704 Isaac Newton Proposed a mechanical universe with small solid masses in motion.

1803 John DaltonProposed an "atomic theory" with spherical solid atoms based upon measurab

properties of mass.

1832 Michael Faraday

Studied the effect of electricity on solutions, coined term "electrolysis" as a s

molecules with electricity, developed laws of electrolysis. Faraday himself w

proponent of atomism.

1859 J. Plucker Built one of the first gas discharge tubes ("cathode ray tube").

1869 Dmitri MendeleevArranged elements into 7 groups with similar properties. He discovered thatproperties of elements "were periodic functions of the their atomic weights"

became known as the Periodic Law.

1873James ClerkMaxwell Proposed electric and magnetic fields filled the void.

1879Sir William

Crookes

Discovered cathode rays had the following properties: travel in straight line

cathode; cause glass to fluoresce; impart a negative charge to objects they s

deflected by electric fields and magnets to suggest a negative charge; cause in their path to spin indicating they have mass.

1886 E. GoldsteinUsed a CRT to study "canal rays" which had electrical and magnetic properti

of an electron.

1894 G.J. StoneyProposed that electricity was made of discrete negative particles he calledele(Link to info on electrons)

1895 Wilhelm Roentgen

Using a CRT he observed that nearby chemicals glowed. Further experiment

very penetrating rays coming from the CRT that were not deflected by a magHe named them "X-rays".

1896 Henri BecquerelWhile studying the effect of x-rays on photographic film, he discovered some

spontaneously decompose and give off very pentrating rays.

1897 J.J. ThomsonUsed aCRT to experimentally determine the charge to mass ratio(e/m) of an

=1.759 x 10 8 coulombs/gram.

1897 J.J. Thomson Studied "canal rays" and found they were associated with the proton H + .

1898 Rutherford Studied radiations emitted from uranium and thorium and named them alpha

1898Marie Sklodowska

Curie

Studied uranium and thorium and called their spontaneous decay process

"radioactivity". She and her husband Pierre also discovered the radioactive el

polonium and radium.

1900 SoddyObserved spontaneous disintegration of radioactive elements into variants he"isotopes" or totally new elements, discovered "half-life", made initial calcul

energy released during decay.

1900 Max Planck used the idea of quanta (discrete units of energy) to explain hot glowing matt

1903 NagaokaPostulated a "Saturnian" model of the atom with flat rings of electrons revolv

a positively charged particle.

http://www.perseus.tufts.edu/GreekScience/Students/Marc/short_paper.htmlhttp://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Newton.htmlhttp://web.lemoyne.edu/~giunta/dalton.htmlhttp://www.chemteam.info/Chem-History/Faraday-Chlorine-1823.htmlhttp://www.woodrow.org/teachers/ci/1992/Mendeleev.htmlhttp://www.treasure-troves.com/bios/Maxwell.htmlhttp://www.treasure-troves.com/bios/Maxwell.htmlhttp://www.chem.ox.ac.uk/icl/heyes/LanthAct/Biogs/Crookes.htmlhttp://www.chem.ox.ac.uk/icl/heyes/LanthAct/Biogs/Crookes.htmlhttp://www.chemteam.info/Chem-History/Stoney-1894.htmlhttp://web.lemoyne.edu/~giunta/papers.htmlhttp://web.lemoyne.edu/~giunta/papers.htmlhttp://nobelprize.org/nobel_prizes/physics/laureates/1901/rontgen-bio.htmlhttp://www.physics.isu.edu/radinf/cuire.htmhttp://www.chemteam.info/Chem-History/Thomson-Structure-Atom.htmlhttp://scienceworld.wolfram.com/physics/CathodeRayTube.htmlhttp://scienceworld.wolfram.com/physics/CathodeRayTube.htmlhttp://scienceworld.wolfram.com/physics/CathodeRayTube.htmlhttp://phoenix.phys.clemson.edu/labs/cupol/eoverm/http://phoenix.phys.clemson.edu/labs/cupol/eoverm/http://www.aip.org/history/electron/jjhome.htmhttp://www.treasure-troves.com/bios/Rutherford.htmlhttp://nobelprize.org/nobel_prizes/chemistry/laureates/1911/marie-curie-bio.htmlhttp://nobelprize.org/nobel_prizes/chemistry/laureates/1911/marie-curie-bio.htmlhttp://web.lemoyne.edu/~giunta/dalton.htmlhttp://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.htmlhttp://www.chemteam.info/Chem-History/Nagaoka-1904.htmlhttp://www.chemteam.info/Chem-History/Nagaoka-1904.htmlhttp://nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.htmlhttp://web.lemoyne.edu/~giunta/dalton.htmlhttp://nobelprize.org/nobel_prizes/chemistry/laureates/1911/marie-curie-bio.htmlhttp://nobelprize.org/nobel_prizes/chemistry/laureates/1911/marie-curie-bio.htmlhttp://www.treasure-troves.com/bios/Rutherford.htmlhttp://www.aip.org/history/electron/jjhome.htmhttp://phoenix.phys.clemson.edu/labs/cupol/eoverm/http://scienceworld.wolfram.com/physics/CathodeRayTube.htmlhttp://www.chemteam.info/Chem-History/Thomson-Structure-Atom.htmlhttp://www.physics.isu.edu/radinf/cuire.htmhttp://nobelprize.org/nobel_prizes/physics/laureates/1901/rontgen-bio.htmlhttp://web.lemoyne.edu/~giunta/papers.htmlhttp://www.chemteam.info/Chem-History/Stoney-1894.htmlhttp://www.chem.ox.ac.uk/icl/heyes/LanthAct/Biogs/Crookes.htmlhttp://www.chem.ox.ac.uk/icl/heyes/LanthAct/Biogs/Crookes.htmlhttp://www.treasure-troves.com/bios/Maxwell.htmlhttp://www.treasure-troves.com/bios/Maxwell.htmlhttp://www.woodrow.org/teachers/ci/1992/Mendeleev.htmlhttp://www.chemteam.info/Chem-History/Faraday-Chlorine-1823.htmlhttp://web.lemoyne.edu/~giunta/dalton.htmlhttp://www-gap.dcs.st-and.ac.uk/~history/Mathematicians/Newton.htmlhttp://www.perseus.tufts.edu/GreekScience/Students/Marc/short_paper.html

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1904 AbeggDiscovered that inert gases had a stable electron configuration which lead to chemical inactivity.

1905 Albert Einstein Published the famous equationE=mc 2

1906 Hans Geiger Developed an electrical device to "click" when hit with alpha particles.

1909 R.A. MillikanOil drop experiment determined the charge (e=1.602 x 10 -19 coulomb) and (m = 9.11 x 10 -28 gram) of an electron.

1911 Ernest Rutherford

Using alpha particles as atomic bullets, probed the atoms in a piece of thin (0

cm)gold foil . He established that the nucleus was: very dense,very small an

charged. He also assumed that the electrons were located outside the nucleus

1914 H.G.J. Moseley

Using x-ray tubes, determined the charges on the nuclei of most atoms. He w

atomic number of an element is equal to the number of protons in the nucleu

work was used to reorganize the periodic table based upon atomic number in

atomic mass.

1919 Aston Discovered the existence of isotopes through the use of a mass spectrograph.

1922 Niels Bohr

Developed an explanation of atomic structure that underlies regularities of t

table of elements. His atomic model had atoms built up of sucessive orbital selectrons.

1923 de BroglieDiscovered that electrons had a dual nature-similar to both particles and wav

Particle/wave duality. Supported Einstein.

1927 Heisenberg

Described atoms by means of formula connected to the frequencies of spec

Proposed Principle of Indeterminancy - you can not know both the position aof a particle.

1929Cockcroft /

Walton

Built an early linear accelerator and bombarded lithium with protons to produ

particles

1930 SchrodingerViewed electrons as continuous clouds and introduced "wave mechanics" as

mathematical model of the atom.

1930 Paul DiracProposed anti-particles . Anderson discovered the anti-electron (positron) in

Segre/Chamberlain detected the anti-proton in 1955..

1932 James ChadwickUsing alpha particles discovered a neutral atomic particle with a mass close t

Thus was discovered the neutron.

1938Lise Meitner,Hahn , Strassman

Conducted experiments verifying that heavy elements capture neutrons and

unstable products which undergo fission. This process ejects more neutrons

the fission chain reaction.

1941 -51

Glenn SeaborgSynthesized 6 transuranium elements and suggested a change in the layout ofperiodic table.

1942 Enrico Fermi Conducted the first controlled chain reaction releasing energy from the atom1950's

-

New

findings/particlesFollow this link to current theories about atomic stucture.

http://www.aip.org/history/einstein/http://www.aip.org/history/einstein/emc1.htmhttp://www.aip.org/history/einstein/emc1.htmhttp://www.nobel.se/physics/laureates/1990/press.htmlhttp://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.htmlhttp://www.rutherford.org.nz/http://micro.magnet.fsu.edu/electromag/java/rutherford/http://micro.magnet.fsu.edu/electromag/java/rutherford/http://micro.magnet.fsu.edu/electromag/java/rutherford/http://wapedia.mobi/en/Henry_Moseleyhttp://www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.htmlhttp://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Broglie.htmlhttp://www.aip.org/history/heisenberg/p01.htmhttp://www.facstaff.bucknell.edu/mvigeant/univ_270_03/Jaime/History.htmlhttp://www.facstaff.bucknell.edu/mvigeant/univ_270_03/Jaime/History.htmlhttp://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Schrodinger.htmlhttp://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-bio.htmlhttp://chemcases.com/nuclear/nc-01.htmhttp://www.sdsc.edu/ScienceWomen/meitner.htmlhttp://www.chemheritage.org/classroom/chemach/atomic/hahn-meitner.htmlhttp://www.chemheritage.org/classroom/chemach/atomic/hahn-meitner.htmlhttp://nobelprize.org/nobel_prizes/chemistry/laureates/1951/seaborg-bio.htmlhttp://www.osti.gov/accomplishments/fermi.htmlhttp://particleadventure.org/index.htmlhttp://particleadventure.org/index.htmlhttp://particleadventure.org/index.htmlhttp://particleadventure.org/index.htmlhttp://www.osti.gov/accomplishments/fermi.htmlhttp://nobelprize.org/nobel_prizes/chemistry/laureates/1951/seaborg-bio.htmlhttp://www.chemheritage.org/classroom/chemach/atomic/hahn-meitner.htmlhttp://www.sdsc.edu/ScienceWomen/meitner.htmlhttp://chemcases.com/nuclear/nc-01.htmhttp://nobelprize.org/nobel_prizes/physics/laureates/1933/dirac-bio.htmlhttp://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Schrodinger.htmlhttp://www.facstaff.bucknell.edu/mvigeant/univ_270_03/Jaime/History.htmlhttp://www.facstaff.bucknell.edu/mvigeant/univ_270_03/Jaime/History.htmlhttp://www.aip.org/history/heisenberg/p01.htmhttp://www-groups.dcs.st-and.ac.uk/~history/Mathematicians/Broglie.htmlhttp://www2.lucidcafe.com/lucidcafe/library/95oct/nbohr.htmlhttp://wapedia.mobi/en/Henry_Moseleyhttp://micro.magnet.fsu.edu/electromag/java/rutherford/http://www.rutherford.org.nz/http://nobelprize.org/nobel_prizes/physics/laureates/1923/millikan-bio.htmlhttp://www.nobel.se/physics/laureates/1990/press.htmlhttp://www.aip.org/history/einstein/emc1.htmhttp://www.aip.org/history/einstein/