Periodicity

• Overall trend across period 3 is a decrease in atomic radius:

  As they are in the same energy level therefore similar shielding

  increased nuclear chare therefore stronger attraction with the nucleus
• Ionisation energy: General increases across the group

  Deviations:

  Mg-Al as outer electron in 3p subshell therefore weaker attraction to the nucleus + more shielding

  P-S - S has a pair of electrons in its 3p subshell therefore more repulsion so less ionisation energy
• Melting points of Na, Mg and Al

  High melting and boiling points as lots of energy required to overcome strong electrostatic forces of attraction between the sea of delocalised electrons and the positive metal ions

  As the ions get bigger stronger nuclear charge therefore higher melting points
• Si is simple molecular therefore has lots of strong covalent bonds which require lots of energy to be broken
• P4, S8 or Cl2 is simple molecular weaker van der Waals forces of attraction as the molecules get bigger, stronger van der Waals