kaminski.judge.atomichistory.fall.2009

Atomic History Timeline Kreg Kaminski Christopher Judge



Democritus · Hypothesized that all matter is composed of small indestructible particles called atoms ·  Also believed that atoms are always in motion.

John Dalton ·  Formalized a theory of atoms that received broad acceptance. Atomic Theory 1.  Each element is composed of tiny indestructible particles called atoms. 2.  All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements. 3.  Atoms combine in simple whole-number ratios to form compounds. 4. A chemical reaction is a rearrangement of atoms

Wilhelm C. Roentgen

· In 1895 Roentgen created the world’s first X-ray. The x-ray was of his wife’s hand as shown to the left. Wilhem discovered that when cathode rays struck certain materials (copper for example) a different type of ray was emitted. · He observed that the x-ray had three properties 1.)The could pass unimpeded through many objects 2.)They were unaffected by magnetic or electric fields 3.)They produced an image on photographic plates Henri Becquerel ·   He was observing materials which would emit light after being exposed to sunlight. After Roentgen’s discovery of x-rays Henri was curious if also emit x- rays. He discovered that uranium containing minerals produced x-ray radiation, high energy photons.   ·   Henri also discovered that the rays emitted by uranium caused gases to ionize and that they were different from X-rays because they could be deflected by electric or magnetic fields.   ·   In 1903 he received half of the nobel prize for spontaneous radioactivity.

JJ. Thomson

·  In 1897 Thomson changed the world’s view of the atom with the discovery of electrons. ·  The electron was a smaller and more fundamental particle and at the time was difficult to understand. ·  Thomson came up with the Plum Pudding Model (to the right) witch had electrons scattered throughout in a sphere of positive charge. // Cathode Ray Tubes // ·  The Cathade Ray Tube was a cylinder had two slits in it, leading to electrometers and it could measure small electric charges. Niels Bohr · Bohr discovered that Ernest Rutherford's theory of the atomic structure was not completely correct. Bohr

