ionisation energies

• first ionisation enthalpy

  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
• factors affecting ionisation energy:

  • atomic radius
  • nuclear charge
  • electron shielding
• successive ionisation energies

  energy it takes to remove all electrons one by one
• increases if the electrons go down a sub-shell
• first ionisation energy decreases down a group
• increases if electrons go down a sub-shell
• ionisation energy increases across a period as nuclear charge increases but atomic size also increases so there is less attraction between nucleus and outer shell electrons, this means that the increase in positive charge is outweighed by the decrease in negative charge
• ionisation energy increases up a group because the number of protons stays constant but the number of electrons increases which makes the attraction stronger
• more endothermic

  requires more energy