Ionisation energy

• What is the meaning of the term ionisation?


  Ionisation refers to the process of removing an electron from an atom or molecule.
• How is first ionisation energy defined?


  First ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions.
• What is the equation for the first ionisation of oxygen?


  O(g) → O*(g) + e⁻
• What is the first ionisation energy of oxygen in kJ mol⁻¹?


  +1314 kJ mol⁻¹
• Why must the gas state symbol (g) be used in ionisation energy equations?


  Because ionisation energies are measured for gaseous atoms.
• What does a lower ionisation energy indicate?


  A lower ionisation energy indicates that it is easier to form a positive ion.
• What are the three factors that affect ionisation energy?

  • Nuclear charge: More protons increase attraction.
  • Distance from nucleus: Electrons further away are less attracted.
  • Shielding: Inner electrons reduce the attraction felt by outer electrons.
• How does nuclear charge affect ionisation energy?


  More protons in the nucleus result in a stronger attraction for the electrons.
• How does distance from the nucleus affect ionisation energy?


  Attraction falls off rapidly with distance, so electrons close to the nucleus are more strongly attracted.
• What is shielding in the context of ionisation energy?


  Shielding is the reduction of attraction felt by outer electrons due to inner electron shells.
• What is another term that might be used for ionisation energy?


  Ionisation enthalpy
• Why is ionisation considered an endothermic process?


  Because energy must be supplied to remove an electron from an atom or molecule.
• What is the first ionisation energy of lithium in kJ mol⁻¹?


  +519 kJ mol⁻¹
• What is the first ionisation energy of sodium in kJ mol⁻¹?


  +496 kJ mol⁻¹
• Why does lithium have a higher first ionisation energy than sodium?


  Because lithium has a smaller atomic radius and less shielding effect.
• What is the second ionisation energy?


  The second ionisation energy is the energy needed to remove an electron from each ion in 1 mole of gaseous 1+ ions.
• What is the equation for the second ionisation of oxygen?

  O+(g) → O2+(g) + e−
• Why are second ionisation energies greater than first ionisation energies?


  Because the electron is being removed from a positive ion, which requires more energy.
• How does the electron configuration affect second ionisation energy?


  The electron configuration determines how much larger the second ionisation energy is compared to the first.
• What happens to the ionisation energy as you remove successive electrons?


  Successive ionisation energies increase because electrons are removed from an increasingly positive ion.
• What is the general equation for the nth ionisation?

  Xn+(g) → Xn+1+(g) + e−
• What is the trend in first ionisation energy down Group 2?


  First ionisation energy decreases down Group 2.
• Why does first ionisation energy decrease down Group 2?


  Because extra electron shells shield outer electrons from the nucleus and increase distance.
• What is the trend in first ionisation energy across Period 3?


  First ionisation energy generally increases across Period 3.
• What causes the increase in ionisation energy across Period 3?


  The increase is due to the increasing number of protons, resulting in stronger nuclear attraction.
• What is the significance of the small drops in ionisation energy between Groups 2 and 3, and 5 and 6?


  These drops indicate sub-shell structure and electron repulsion effects.
• Why does the ionisation energy drop between Groups 2 and 3?


  Because aluminium's outer electron is in a 3p orbital, which is at a higher energy level than the 3s orbital.
• What causes the drop in ionisation energy between Groups 5 and 6?


  The drop is due to electron repulsion when removing an electron from a shared orbital.
• How can successive ionisation energies provide evidence for shell structure?


  Successive ionisation energies increase as electrons are removed from an increasingly positive ion, showing the strength of attraction to the nucleus.
• How can you determine the group number of an element from its successive ionisation energies graph?


  Count how many electrons are removed before the first big jump in ionisation energy.
• What does the graph of successive ionisation energies indicate about sodium's group number?


  Sodium is in Group 1, as one electron is removed before the first big jump.
• What can be inferred from the pattern of successive ionisation energies in terms of electron configuration?


  • The number of electrons in each shell can be determined.
  • The group of the element can be identified.
  • Big jumps indicate the removal of electrons from a new shell.
• What is the first ionisation energy of magnesium in kJ mol⁻¹?


  +738 kJ mol⁻¹
• What is the first ionisation energy of aluminium in kJ mol⁻¹?


  +578 kJ mol⁻¹
• Why does aluminium have a lower first ionisation energy than magnesium?


  Because aluminium's outer electron is in a higher energy 3p orbital compared to magnesium's 3s orbital.
• What is the first ionisation energy of phosphorus in kJ mol⁻¹?


  +1012 kJ mol⁻¹
• What is the first ionisation energy of sulfur in kJ mol⁻¹?


  +1000 kJ mol⁻¹
• Why does sulfur have a lower first ionisation energy than phosphorus?


  Because the electron being removed from sulfur is from a shared orbital, which experiences repulsion.
• What is the significance of drawing electron configurations when studying ionisation energies?


  Drawing electron configurations helps to visualize which electrons are being removed and their interactions.
• What is the trend in ionisation energy as you go down a group in the periodic table?


  Ionisation energy generally decreases as you go down a group.