IONISATION ENERGY 1

IONISATION ENERGY 1

1. WHAT IS IONISATION ENERGY?

   • A measure of the amount of energy needed to remove electrons from atoms
   • First ionisation energy definition
     • Then energy required to remove 1 mole of electrons (to infinity) from 1 mole of gaseous atoms to form 1 mole of gaseous positive ions
   • As electrons are negatively charged and protons in the nucleus are, there will be an attraction between them.
     • The greater the pull of the nucleus, the harder it will be to pull an electron away from an atom

2. 1st ionisation energy - Hydrogen - Helium - Lithium

   • The value of the first ionisation energy depends on the electronic structure
   • Helium
     • The energy needed to remove the electron for helium is higher than that for hydrogen because there are now 2 protons in the nucleus.
       • The nuclear charge is greater so the pull on the outer electron is larger. More energy will be needed to pull an electron out from the atom
   • Lithium
     • Lithium atoms have 3 protons so you would expect the pull on electrons to be greater ...
       • However, the 1st ionisation energy of Lithium is lower than that of helium because:
         • 1) The filled inner shells exert a shielding effect, which in turn lowers the effective nuclear pull.
         • 2) the electron is further away from the nucleus ; lower nuclear attraction for an electron

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