ionisation energy

• Second ionisation energy


  The energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
• Shell (electron shell)

  A group of atomic orbitals with the same principal quantum number. Also known as a main energy level.
• Shielding effect

  The repulsion between electrons in different inner shells. Shielding reduces the net attractive force between the positive nucleus on the outer shell electrons.
• Sub-shell

  A group of orbitals of the same type within a shell.
• Principal quantum number, n

  A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The sets of orbitals with the same n-value are referred to as electron shells or energy levels.
• First ionisation energy

  The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
• Why do successive ionisation energies increase with ionisation number?

  • radius decreases
  • attraction between remaining electrons and nucleus increases
• First ionisation energy is the energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions
• First ionisation equation for sodium

  Na (g) -> Na+ (g) + e-
• Second ionisation energy is the energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
• Second ionisation equation for helium

  He+ (g) -> He2+ (g) + e-
• Factors affecting ionisation energy:

  • atomic radius
  • nuclear charge
  • electron shielding
• Nuclear charge: the more protons in the nucleus, the greater attraction between the nucleus and outer electrons
• Shielding effect reduces the attraction between the nucleus and outer electrons
• Predictions that can be made from successive ionisation energies:

  • the number of electrons in the outer shell
  • the group of the element in the periodic table
  • the identity of the element
• Across a period

  • nuclear charge increases
  • similar shielding
  • nuclear attraction increases
  • atomic radius decreases
  • 1IE increases
• Down a group

  • atomic radius increases
  • shielding increases
  • nuclear attraction on outer electrons decreases
  • 1IE decreases