Periodicity

• Periodic table


  Elements are arranged in the order of increasing atomic numbers
• Period


  The horizontal rows in the periodic table
• Group


  The vertical columns in the periodic table
• Periodicity


  The repeating trends in chemical and physical properties
• Across each period


  • Elements change from metals to non metals
• Electron configuration shorthand


  The noble gas before the element is used to abbreviate. E.g Li → [He] 2s1
• First ionisation energy


  The energy required to remove one electron from each atom in one mole of the gaseous element to form one mole of gaseous 1+ ions
• First ionisation energy of magnesium

  Mg (g) → Mg+ (g) + e
• Factors affecting ionisation energy

  • Atomic radius
  • Nuclear charge
  • Electron shielding or screening
• Across period 3


  First ionisation energy increases due to: increased nuclear charge, decreased atomic radius, same electron shielding
• First ionisation energy dips at Al

  Outer electron is in a 3p orbital, higher energy than 3s orbital → less energy needed to remove electron
• First ionisation energy dips at S


  One 3p orbital contains two electrons → repulsion between paired electrons → less energy needed to remove one
• First ionisation energy decreases between group 2 to 3


  In group 3 the outermost electrons are in p orbitals whereas in group 2 they are in s orbital, so the electrons are easier to be removed
• First ionisation energy decreases between group 5 to 6


  The group 5 electrons in p orbital are single electrons and in group 6 the outermost electrons are spin paired, with some repulsion. Therefore the electrons are slightly easier to remove
• First ionisation energy between the end of one period and the start of next


  Decreases due to increase in atomic radius and increase in electron shielding
• First ionisation energy down a group


  Decreases due to increased shielding, weaker attraction, and increased distance between outer electrons and nucleus
• Properties of giant metallic lattices

  • High melting and boiling point
  • Good electrical conductors
  • Malleability
  • Ductility
• Ductile metal


  The metal can be made stretched. E.g Can be made into wires
• Malleable metal


  The metal can be shaped into different forms
• Structure, forces and bonding in elements across period 2

  • Li & Be → giant metallic ; strong attraction between positive ions and delocalised electrons ; metallic bonding
  • B & C → giant covalent ; strong forces between atoms ; covalent
  • N2, O2, F2, Ne → simple molecular ; weak intermolecular forces between molecules ; covalent bonding within molecules and intermolecular forces between molecules
• Structure, forces and bonding in elements across period 3


  • Na, Mg, Al → giant metallic ; strong attraction between positive ions and delocalised electrons ; metallic bonding
  • Si → giant covalent ; strong forces between atoms ; covalent
  • P4, S8, Cl2, Ar → simple molecular ; weak intermolecular forces between molecules ; covalent bonding within molecules and intermolecular forces between molecules