Periodicity

• Periodicity is a group of elements with similar patterns or trends
• In Period 3:

  Atomic radius decreases across a period

  As elements are in the same energy level so similar shielding

  Increased nuclear charge so stronger attraction
• In period 3:

  General increase in ionisation but there are a few deviations

  Mg to Al: Al has its outer electron in the 3p subshell therefore weaker attraction to the nucleus and more shielding so decrease in ionisation energy

  P to S: S has a pair of electrons in the 3p subshell therefore has more repulsion therefore a decrease in ionisation energy
• Na, Mg, Al have metallic bonding strong electrostatic forces between a sea of delocalised electrons and positive metal ions

  Si has a macromolecular structure, lots of energy required to break strong covalent bonds

  P, S and Cl has simple molecular structure, Little energy required to overcome weak van der Waals forces of attraction