PERIODIC ELEMENTS

• Paracelsus (1493-1541) introduced the three alchemical symbols salt, sulfur, and mercury
• Salt


  The fixed part left after burning (calcination)
• Sulfur


  The principle of combustability
• Mercury


  The essential part of all metals
• The first discovery of a true element in historical time was that of phosphorus by Dr. Brand of Hamburg, in 1669
• For the next two and three-quarters centuries chemists had much fun and some fame discovering new elements
• Scheele made chlorine in 1774 by the action of "black manganese" (manganese dioxide) on concentrated muriatic acid (hydrochloric acid)
• Chlorine was not recognized as an element till the work of Davy in 1810
• Johann Dobereiner arranged the three elements in order of the increasing atomic mass
• The average of the masses of the lightest and the heaviest elements was very close to the atomic mass of the middle element
• Johann Dobereiner's arrangement of elements is known as the Law of Triad
• John Newlands 1864 Noted that if the elements starting from hydrogen were arranged in the order of increasing atomic mass
• Similar properties would repeat every eighth element also call a law of octaves
• Dmitri Mendeleev and Julius Lothar Meyer proposed a more extensive tabulation of the elements based on the regular, periodic occurrence properties
• Mendeleev proposed the existence of an unknown element he called eka-aluminum and predicted a number of its properties
• Henry Moseley


  • Found that atomic number increases in the same order as atomic mass
• Periodic Law


  • When the elements are arranged in the order of increasing atomic number, elements with similar properties appear at the periodic intervals
• In 1919, Rutherford accomplished scientifically what medieval alchemists had failed to do with "magic" experiments and other less sophisticated techniques
• Rutherford didn't find gold (the goal of the alchemists) but something more valuable with even greater potential for good and evil
• Rutherford found a method of transmuting one element into another
• Transmuting one element into another

  1. Bombarding nitrogen nuclei with alpha particles from radium

  2. Nitrogen was changed into oxygen
• Unknown elements in the periodic table (43,61,85,87)


  1925
• Elements 43 and 85 were synthesized using particle accelerators
• Cyclotron


  1. Produces high-energy particles

  2. Heavy target nuclei are hit by the high-energy particles

  3. Heavier nuclei are produced from the cyclotron upon hitting heavy target nuclei
• Bombarding of Mo with deuteron

  • Formed technicium which is the first artificially made element
• Technicium


  The first artificially made element, formed by bombarding Mo with deuteron
• Technicium

  Derived from the Greek word technetos which means artificial
• Element 85 were discovered

  1940
• Element 85 was discovered by Dale Corson, K. Mackenzie and Emilio Segre
• Discovery of Element 85

  Bismuth 83 (Bi) was bombarded with a fast moving alpha particles through a cyclotron
• Element 85

  Astatine (astatos meaning unstable)
• Element 61 and 87 were discovered through the study of radioactivity
• Element 61

  Promethium
• Promethium


  Decay product of the fission of Uranium
• Element 87

  Francium
• Francium


  Breakdown product of Uranium
• Transuranic Elements

  are synthetic elements with atomic numbers higher than that of Uranium (Z=92).