Melting Points: Metallic Bonding
The first three elements of Period 3 (sodium, magnesium, and aluminium) show an increasing trend in melting points. Sodium melts at just 98°C, while aluminium doesn't melt until it reaches 660°C. This significant difference reveals important principles about metallic bonding.
The increase in melting points occurs because the metallic bonds become stronger across these three elements. Each metal forms a lattice of positive ions surrounded by a "sea" of delocalised electrons. As you move from sodium to aluminium, the charge on the metal ions increases (Na⁺, Mg²⁺, Al³⁺), providing more electrons to the delocalised sea.
This increased positive charge, combined with smaller ionic radii, creates stronger electrostatic attractions between the positive metal ions and the negative electron sea. Consequently, more energy is required to overcome these attractions, resulting in higher melting points.
Make the Connection: The pattern in melting points of metals directly connects to their electron configurations. Sodium loses 1 electron (melts easily), magnesium loses 2 (melts at higher temperature), and aluminium loses 3 (requires even more heat to melt).