periodicity

• Periodic Table


  Arranges the known elements according to proton number
• Period


  • All the elements along a period have the same number of electron shells
• Group


  • All the elements down a group have the same number of outer electrons, this number is indicated by the group number
• Blocks in the Periodic Table

  • s-block (groups 1 and 2)
  • p-block (groups 3 to 0)
  • d-block (transition metals)
  • f-block (radioactive elements)
• Electron configurations of the blocks are often linked to other trends within the Periodic Table
• Periodicity


  The study of trends in the Periodic Table
• Along a period


  Atomic radius decreases
• Reason for atomic radius decreasing along a period


  Increased nuclear charge for the same number of electron shells, pulling the outer electrons closer to the nucleus
• Down a group


  Atomic radius increases
• Reason for atomic radius increasing down a group

  Addition of an electron shell each time, increasing the distance between the outer electrons and the nucleus, and increased electron shielding reducing nuclear attraction
• Along a period


  Ionisation energy increases
• Reason for ionisation energy increasing along a period

  Decreasing atomic radius and increasing nuclear charge means the outer electrons are held more strongly, requiring more energy to remove them
• Down a group


  Ionisation energy decreases
• Reason for ionisation energy decreasing down a group

  Reduced nuclear attraction between the nucleus and outer electrons, and increased electron shielding means less energy is required to remove the outer electron
• Metallic bonding


  Bonding in sodium, magnesium and aluminium, with increasing positive charge of the ions and more released free electrons leading to higher melting points
• Covalent structure


  Very strong bonding in silicon, requiring a lot of energy to break, leading to a high melting point
• Simple covalent molecules


  Bonding in phosphorus, sulphur and chlorine, held by weak van der Waals forces which are easy to overcome, leading to low, similar melting points
• Noble gas


  Argon has a full outer shell of electrons, making the atoms very stable with very weak van der Waals forces, leading to a very low melting point and existing as a gas at room temperature