Modern periodic table

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  • Created by: Georgia
  • Created on: 18-04-13 17:51
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  • The modern Periodic Table
    • not all scientists thought periodic table was important
      • when the periodic table first came out, scientists thought it was just a bit of fun
        • wasn't much evidence to suggest elements did fit together like that
      • after Mendeleev released work, newly discovered elements fitted in gaps
        • this was convincing evidence in favour of the table
      • once there was more evidence scientists realised periodic table was useful
        • useful for predicting properties of elements
      • in late 19th  century, scientists discovered protons, neutrons and electrons
        • table matched up well with what had been discovered about the atom
          • scientists now accept it's importance and useful summary of structure of atoms.
    • modern periodic table is based on electronic structure
      • elements in periodic table can be seen as being arranged by their electronic structure
        • using electron arrangement,can predict chemical properties
      • electron in atoms are set out in shells which each correspond to an energy level
      • apart from transition metals, elements in same group have the same number of electrons in their outer shell
      • positive charge of nucleus attracts electrons and holds them in place
        • the further from the nucleus the electron is, the less the attraction
      • the attraction of the nucleus is even less when there are a lot of inner electrons
        • inner electrons 'get in the way' of the nucleus charge, reducing attraction
          • this is known as shielding
      • the combination of increased distance and increased shielding means that an electron in a higher energy level is more easily lost
        • as there's less attraction from nucleus holding it in place
          • this is why group 1 metals get more reactive as you go down group
      • increased distance and shielding means higher energy level is less likely to gain an electron
        • that's why group 7 elements are less reactive as you go down group

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