Electron arrangements and ionisation energy

• Ionisation energy = The energy needed to remove an electron from an atom

  • Ionisation energy is the energy required to remove a mole of electrons from a mole of atoms in a gaseous state (measured by kJ mol-1)
• Removing electrons from an atom


  1st removed requires the least energy because the atom at this point is neutral

  It gets harder to remove electrons as more are removed (succsessive ionisation energies)
• Trends in IE across a period

  Generally increase because the nuclear charge increases and therefore makes it harder to remove an electron
• Trends in IE down a group


  General decrease in 1st IE because the outer electron is in an orbital by itself.
• Going down a group:

  • Nuclear charge increases
  • But distance decreases
  • And shielding increases