Periodicity

• Along a period, atomic radius decreases as the proton number increases, so e-s are pulled closer together because of the increased attraction
• Ionisation energy increases because there's a stronger attraction between the nucleus and outer electron -> more energy needed to ionise the atom
• Na, Mg, Al have metallic bonding so there mp increase due to increased attraction between positively charged ions and negative electrons
• Silicon is a macromolecular molecule so it has strong covalent bonds -> high mp
• P, S, Cl are simple covalent molecules and have weak van der waals forces -> low mp