Chemistry AS ES CI 2.5

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  • Created by: A.B.
  • Created on: 17-02-14 11:30
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  • ES Atoms and Ions CI 2.5
    • First Ionisation Enthalpy
      • The first ionisation enthalpy is the energy needed to remove one electron from one mole of isolated gaseous atoms of an element.
        • X (g) -> X+ (g) + e-
        • Always positive (energy must be supplied)
      • Trends
        • The elements at the peaks are all in Group 0. It is difficult to remove an electron from these atoms with full outer shells and the elements are very unreactive.
        • The elements at the troughs are all in group 1 (alkali metals ). These atoms have only one outer shell electron and are relatively easy to ionise. They are all very reactive elements.
      • How does it vary across a period?
        • First ionisation enthalpy increases as atomic number increases.
          • The nuclear charge increases going across the period and the electrons are being added to the same shell so there is greater attraction between the nucleus and electrons.
      • How does it vary down a group?
        • Decrease down the group
          • Attraction between nucleus and outermost electron decreases (electron further with more shielding) -> easier to remove
      • Successive Ionisation Enthalpies
        • The second and subsequent ionisation enthalpies involve the removal of an electron from a positive ion.
        • Patterns
          • Ionisation enthalpies increase as successive electrons are removed.
            • After an electron is removed, the remaining electrons are attracted more strongly to the nucleus.
            • There is a sharp jump in ionisation enthalpy when an electron is removed from a full electron shell.


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