Ionisation Energies

• What is ionisation?

  When an atom gains or loses an electron
• Define first ionisation energy?

  The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of gaseous 1+ ions
• Write the equation for the first ionisation of Oxygen

  
• Factors affecting ionisation energy

  • Nuclear charge
  • Distance from the nucleus
  • Shielding
• How does nuclear charge affect ionisation energy?

  • The more protons there are in the nucleus
  • The more positively charged the nucleus is
  • So the stronger the attraction for the electrons.
• How does the distance from the nucleus affect ionisation energy?

  • Attraction falls off very quickly with distance.
  • An electron close to the nucleus will be much more strongly attracted than one further away.
• How does shielding affect the ionisation energy?

  • As the number of electrons between the outer electrons and the nucleus increases,
  • The outer electrons feel less attraction to the nucleus.
• Write the second ionisation energy of Oxygen

  
• Why are 2nd ionisation energies greater than 1st ionisation energies?

  • The electron is being removed from a positive ion (and not an atom), which will require more energy.
  • The electron configuration plays a role in the difference in ionisation energies
• Ionisation trends in group 2

  • Ionisation energy decreases down group 2
  • Atomic radius increases
  • Shielding increases

  
• Ionisation trends across periods

  • Increases
  • Harder to remove the outer electron as proton number increases
  • So stronger nuclear attraction