Ionisation Energies

• What is involved in ionisation?

  Removing electrons
• What process does ionisation refer to?

  Removing one or more electrons
• Is ionisation an endothermic or exothermic process?

  Endothermic
• Why is ionisation an endothermic process?

  It requires an input of energy
• What does the first ionisation energy refer to?

  Energy needed to remove 1 electron
• What state of matter is involved in first ionisation energy?

  Gaseous
• What type of ions are formed in first ionisation energy?

  1+ ions
• What is the equation representing the first ionisation energy (IE1) of magnesium?

  Mg(g) ➔ Mg+(g) + e−
• What is the ΔHIE1 value for the first ionisation of magnesium?

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

  Ionisation requires energy input
• What does the ionisation energy of an atom depend on?

  Strength of attraction to the nucleus
• What are the three key factors affecting electrostatic attraction and ionization energy?

  Nuclear charge, atomic radius, electron shielding
• How does nuclear charge affect ionisation energy?

  More protons, stronger attraction, higher energy
• How does atomic radius affect ionisation energy?

  Smaller atoms, greater attraction, higher energy
• How does electron shielding affect ionisation energy?

  More shielding, weaker attraction, lower energy
• What leads to high ionisation energies?

  Low shielding and small atomic size
• Why do low shielding and small atomic size lead to high ionization energies?

  Strong electrostatic attraction from nucleus
• What properties of the atom are most influential in trends observed in ionisation energies?

  Nuclear charge, atomic radius, electron shielding
• What is the effect on nuclear charge when moving down a group?

  Increases
• What is the effect on atomic radius when moving down a group?

  Increases
• What is the effect on electron shielding when moving down a group?

  Increases
• Why does ionisation energy decrease down groups, despite increasing nuclear charge?

  Atomic radius and shielding outweigh nuclear charge
• What is the effect on nuclear charge when moving across a period?

  Increases
• What is the effect on atomic radius when moving across a period?

  Decreases
• What is the effect on electron shielding when moving across a period?

  Stays similar
• Why does ionisation energy generally increase across periods?

  Increasing nuclear charge outweighs similar shielding
• Where are there exceptions to the increasing ionization energy trend across periods?

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

  Electron removed from p orbital instead of s
• Why do p orbitals have slightly higher energy than s orbitals?

  Outermost electron is further from nucleus
• How does the p orbital experience additional shielding compared to s orbitals?

  Shielding from s electrons
• Why does aluminium have a lower first ionisation energy than magnesium?

  Aluminium's electron from p orbital
• Why is there a drop in ionisation energy between groups 5 and 6?

  Electron removed from paired orbital in group 6
• What is the electron configuration of group 5 elements?

  Electron removed from a singly occupied orbital
• What is the electron configuration of group 6 elements?

  Electron removed from an orbital containing two electrons
• What effect do paired electrons have in group 6 elements?

  Greater electron-electron repulsion
• Why does sulfur have a lower first ionisation energy than phosphorus?

  Sulfur's electron from paired orbital
• What are successive ionisation energies?

  Energy to remove each electron
• What is the second ionisation energy?

  Energy needed to remove 1 electron from 1+ ion
• What is the equation representing the second ionisation energy (IE2) of magnesium?

  Mg+(g) → Mg2+(g) + e−
• What is the ΔHIE2 value for the second ionisation of magnesium?

  +1,451 kJ mol−1