Ionisation Energy

• The first ionisation energy is the amount of energy required to remove one mole of electrons from one mole of gaseous atoms
• Factors affecting ionisation energy

  • shielding
  • nuclear charge
  • distance from nucleus
• as you move across a period, the general trend is for ionisation energies to increase as the nuclear charge increases and the atomic radium decreases however there are small drops between groups 2 and 3 and groups 5 and 6
• the drop in ionisation energy between group 2 and 3 across period 3 is due to aluminium's outer electron being in the 3p orbital so has a higher energy level and more shielding than the 3s orbital
• the drop in ionisation energy between group 5 and 6 across period 3 is because the outer electron is being removed from an orbital containing two electrons and the pair of electron repulse each other