Electronic structure

  • Created by: Rachh
  • Created on: 25-12-12 16:49
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  • Electronic structure
    • Electron shells
      • Electrons have fixed energies.
      • Electrons move around the nucleus in shells, or energy levels.
      • The shells are divided up into sub-shells as the electrons within a shell have different energies.
        • The s- sub-shell has 1 orbital so 2 electrons.
        • The p sub-shell has 3 orbitals so 6 electrons.
        • The d sub-shell has 5 orbitals so 10 electrons.
        • The f sub-shell has 7 orbitals so 14 electrons.
    • Showing electron configurations
      • Sub-shell notation is a way of writing out the configuration of electrons.
        • eg an atom of Neon would be written as 1s2 2s2 2p6
      • Another way to show it is by drawing arrows in boxes.
        • The up and down arrows represent the electrons spinning in different directions.
          • Two electrons can only occupy the same orbital if they have opposite spin.
      • Energy level diagrams are also used.
        • They also show the energy of the electrons in different orbitals.
        • These show the number of electrons and their arrangement.
    • Working out electron configurations
      • Electrons fill up the lowest energy sub-shells first.
      • Electrons fill orbitals singly before they start sharing.
      • For the configuration of ions from the s and p blocks of the periodic table, add or remove electrons to or from the highest energy occupied sub-shell.
        • eg Mg = 1s2 2s2 2p6 3s2 and Mg2+ = 1s2 2s2 2p6
      • Nobe gas symbols in square brackets are sometimes  used in electron configurations.
        • eg calcium (1s2 2s2 2p6 3s2 3p6 4s2) can be shortened to [Ar] 4s2
    • Transition metals:
      • Odd ones out:
        • Copper (Cu): 1s2 2s2 2p6 3s2 3p6 4s1 3d10
        • Chromium (Cr): 1s2 2s2 2p6 3s2 3p6 4s1 3d5
      • When transition metals become ions, they lose their 4s electrons before their 3d electrons.
        • eg. Fe: 1s2 2s2 2p6 3s2 3p6 4s2 3d6 and Fe3+: 1s2 2s2 2p6 3s2 3p6 3d5
    • Electronic structure and chemical properties
      • The s-block elements (group 1 and 2) easily lose their outer electrons to form positive ions with an inert gas configuration.
      • The elements in groups 5,6, and 7 (p block) can gain 1,2 or 3 electrons to form negative ions with an inert gas configuration.
      • Group 0 (the inert gases) have completely filled s and p sub-shells.


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