What is the melting point trend of the Period 3 elements and how does it relate to bonding?

The melting point trend of Period 3 elements increases from sodium to silicon, then decreases.

The melting point trend of Period 3 elements can be explained by the nature of their bonding. Sodium and magnesium have metallic bonding, which involves a sea of delocalized electrons surrounding positively charged metal ions. The strength of metallic bonding is determined by the number of delocalized electrons, which increases as you move from sodium to magnesium. This explains why magnesium has a higher melting point than sodium.

Aluminium has a giant metallic lattice structure, with each atom bonded to eight neighbours. This results in a very strong metallic bond and a high melting point.

Silicon has a giant covalent lattice structure, with each atom bonded to four neighbours. This results in a very strong covalent bond and a high melting point.

Phosphorus, sulfur, chlorine, and argon have simple molecular structures, held together by weak intermolecular forces. As you move from silicon to argon, the number of electrons in the outer shell decreases, resulting in weaker intermolecular forces and a lower melting point.

In conclusion, the melting point trend of Period 3 elements can be explained by the nature of their bonding. Metallic bonding results in high melting points, while covalent and intermolecular bonding result in lower melting points.