Periodicity + Group 3

• Atom size decreases going along a period but increases going down the group.
• Along a period, ionisation energy increases (increased nuclear charge) but going down a group ionisation energy decreases (more shielding).
• In period 3, melting point is dependent on structure and bonding. Sodium, magnesium and aluminium have metallic bonding and the more positive the ion, the higher the melting point. Silicon is a giant covalent structure so has a high melting point. Phosphorus, sulfur and chlorine have a simple covalent molecular structure (van der waals forces only) so have lower melting points.
• Mg(OH)2 is used in medicine.