Periodicity- Ionisation energy

• Across a period


  • Atomic radius decreases
  • Outermost electrons in same shell
  • Nuclear charge increases
  • Nuclear attraction on outermost electrons increases
• Down a Group


  • Atomic radius increases
  • More shells
  • Greater distance of outermost electrons to nucleus
  • Nuclear attraction on outermost electrons decreases (electrons not pulled as close to nucleus)
  • Nuclear charge increase outweighed by more distance & shielding
• Periodic trend in melting points

  Across period 2 and 3, m.p. increases from group 1 to 4. GPS 1-3 have metallic bonding, increasing in strength- stronger forces of attraction, more electrons in outer shell into delocalised electrons & smaller +ve ion. 14 has giant covalent structure. Sharp decrease as simple molecular

  
• Factors affecting Ionisation Energy


  • Attraction from nucleus
  • Atomic radius (↑ distance, ↓ nuclear attraction)
  • Nuclear charge (↑ proton num, ↑ attraction)
  • Electron shielding (↑ shielding, ↓ attraction)
• Ionisation Energy Across a Period


  • Shielding constant
  • Nuclear charge increases
  • Atomic radius decreases
  • ↑ nuclear attraction
  • ∴ ↑ ionisation energy
• Ionisation Energy Down a Group

  • More shells- more shielding
  • Increases nuclear charge
  • Increases atomic radius
  • ↓ nuclear attraction
  • lower ionisation energy
• Decrease in Ionisation energy between Be and B


  5th electron in Boron is in 2p subshell which is higher in energy than 2s subshell (& further from nucleus) so ionisation energy decreases
• Decrease between N and O


  Paired electrons in 2p subshell of O repel, making it easier to remove an electron in oxygen than nitrogen
• Successive Ionisation energy


  The energy required to remove each electron in turn