periodicity

• Trend in atomic radius (period 3)

  Atomic radius decreases
• Reason for decreasing atomic radius

  • Increased number of protons (nuclear charge)
  • Shielding effect = similar
• trend in melting points (period 3)

  increases, then decreases

  • Na -> Mg -> Al -> (metallic bonding)
  • Si (macromolecular structure)
  • P4 < S8 > Cl2 (van der waals forces)
• trend in ionisation energy (period 3)

  ionisation energy increases

  • increased no. protons (nuclear charge)
  • stronger attraction - more energy needed to remove electron
• explain why Mg & Al differ from the trend in ionisation energy

  Mg - 3s orbital

  Al - fills from 3p orbital

  3p electrons are higher in energy and are easier to remove
• explain why P and S differ from the trend in ionisation energy

  pairing repulsion in 3p orbital