Periodicity

• Periodicity is to do with the periodic table and the trends in the properties of elements
• Elements are ordered by

  Proton number, not mass number
• Groups


  Columns in the periodic table, elements in the same group have the same number of electrons in their outer shell
• Periods


  Rows in the periodic table, elements in the same period have the same number of electron shells
• Types of elements by block

  • S-block
  • P-block
  • D-block
  • F-block
• Atomic radius trend across a period

  1. Decreases due to increased nuclear charge pulling in outer electrons

  2. Shielding effect is similar across a period
• Atomic radius trend down a group

  Increases due to more electron shells
• Metallic bonding


  Positive metal ions with delocalized electrons, stronger for higher charge
• Covalent bonding


  Many strong covalent bonds holding atoms together in a giant structure, requires high energy to break
• Simple molecular structure


  Weaker van der Waals forces between small molecules, lower melting point
• Ionization energy


  Minimum energy required to remove one mole of electrons from one mole of atoms in the gaseous state
• Ionization energy trend down a group

  Decreases due to increased atomic radius and shielding
• Ionization energy trend across a period

  Increases due to increased nuclear charge, shielding is similar
• Exceptions to the ionization energy trend across a period are due to electron configuration and electron repulsion effects
• The modern atomic model with subshells explains the exceptions in ionization energy trends across a period