3.2.1 Periodicity

• atomic radius

  distance from nucleus to the electrons in outer energy level
• Period 3 - atomic radius decreases

  • outer electrons all in same energy level - therefore has same shielding
  • nuclear charge increases - gains more protons
• Atomic radius decreases across period 3
• electronegativity

  ability of an atom to attract electron density (electrons) in a covalent bond
• Electronegativity increases across period 3
• Period 3 - electronegativity increases (Na to Cl)

  • nuclear charge increases
  • atomic radius decreases - therefore bonding pair closer to nucleus
  • e- pair in covalent bond more attracted to atoms nucleus
• electronegativity - increases up a group

  • smaller atoms
  • nucleus closer to bonding pair of e-
  • therefore stronger attraction
• stronger attraction between nucleus and outer shell electron = larger ionisation energy
• Period 3 - GENERAL ionisation energy increases

  • atomic radius decreases - outer e- closer to nucleus
  • nuclear charge increases
  • greater attraction between nucleus and outer shell electron
• ionisation energy decreases down a group

  • atomic radius increases - e- further from nucleus
  • weaker attraction between nucleus and outer e-
  • therefore e- easier to remove
• stronger forces between particles = higher melting point
• melting points across period 3 Na to Al

  • melting point increases
  • stronger metallic bonding
  • larger charge density - size of charge larger, ionic radius decreases
  • more delocalised electrons
• melting points across period 3 - silicon

  • 4 strong covalent bonds per silicon atom
  • huge amount of energy required to break
  • melting point high
• melting points across Period 3 - P to Cl

  • molecules held together by weak van der Waals forces
  • van der Waals forces increase with size, number of electrons
  • S8 > P4 > Cl2 - melting points
• melting points across period 3 - Argon

  • lowest melting point
  • weak van der Waals forces between atoms
  • require little energy to break
• periodicity

  study of repeating patterns/trends of physical or chemical properties
• Melting Points across period 3

  A) metallic bonding

  B) giant covalent

  C) simple molecular