1. Discovery of electron 1897 - J.J. Thomson (1856-1940) http://www.chemheritage.org/classroom/chemach/atomic /thomson.html http://www.aip.org/history/electron/ (Kennedy, Chemistry Live!)

2. Mass spectrometry Sample converted to positive ions by collisions with a stream of high energy electrons on entering the spectrometer. Charged sample is accelerated using applied voltage Ions then passed into an evacuated tube and through a magnetic field. Magnetic field causes ions to be deflected by different amounts depending on their mass. Ions with the same mass-to-charge ratio hit the detector at the same spot. ( Brown, LeMay and Bursten, 9 th ed., p.45)

3. Determination of electron charge Robert Millikan (1868 – 1953)

4. Discovery of nucleus 1911 - Ernest Rutherford (1871-1937)

5. Quantum Theory and the Atom Niels Bohr (1885 – 1962) http://www.pa.msu.edu/~brock/d0_homepage/physics- posted/surprises-bohr.html http://www.pbs.org/wgbh/aso/databank/entries/dp13at.html