ionisation energies

• What does ionisation involve?

  Removing electrons
• What is ionisation?

  Removing one or more electrons from an atom
• Why is ionisation considered an endothermic process?

  It requires an input of energy
• What is the first ionisation energy?

  Energy needed to remove 1 electron from 1 mole
• What does the equation Mg(g) ➔ Mg+(g) + e− represent?

  First ionisation energy of magnesium
• What is the value of the first ionisation energy of magnesium?

  +738 kJ mol−1
• Why are ionisation energy values always positive?

  Ionisation requires energy input
• What factors affect ionisation energy?

  • Nuclear charge: More protons increase attraction
  • Atomic radius: Smaller atoms have greater attraction
  • Electron shielding: Inner shells reduce nuclear attraction
• How does nuclear charge affect ionisation energy?

  More protons increase attraction for electrons
• What happens to atomic radius down a group?

  It increases as more electron shells are added
• How does electron shielding affect ionisation energy?

  It reduces the effective nuclear charge experienced
• What leads to high ionisation energies?

  Low shielding and small atomic size
• What are the trends in first ionisation energy down groups?

  • Ionisation energy decreases down groups
  • Nuclear charge increases but atomic radius increases more
  • Electron shielding increases, reducing attraction
• What happens to ionisation energy across periods?

  It generally increases across periods
• Why does ionisation energy increase across periods?

  Increasing nuclear charge outweighs similar shielding
• What are the exceptions in ionisation energy trends?

  Between groups 2-3 and groups 5-6
• Why is there a drop in ionisation energy between groups 2 and 3?

  Electron is removed from a higher energy p orbital
• What is the first ionisation energy of aluminium?

  578 kJ mol−1
• Why is there a drop in ionisation energy between groups 5 and 6?

  Paired electrons experience greater electron-electron repulsion
• What is the first ionisation energy of phosphorus?

  1,011 kJ mol−1
• What is the first ionisation energy of sulfur?

  999 kJ mol−1
• What are successive ionisation energies?

  • Energy to remove each successive electron
  • Example: Second ionisation energy removes from 1+ ions
• What is the second ionisation energy of magnesium?

  +1,451 kJ mol−1
• What happens to successive ionisation energies within the same shell?

  They increase due to greater nuclear attraction
• What causes large jumps in successive ionisation energy?

  Reaching a new inner electron shell
• What is the third ionisation energy of magnesium?

  +7,730 kJ mol−1