9.1.2—Variation in melting point and electrical

Melting points rise when stronger attractions must be overcome. Electrical conductivity requires mobile charged particles or delocalised electrons.

Na, Mg and Al generally strengthen metallic bonding as charge density increases; silicon forms a giant covalent network; molecular elements have lower melting points and limited conductivity.

Al conducts as a metal, silicon conducts less effectively as a semiconductor-like giant covalent solid, and sulfur does not conduct because its S₈ molecules have no mobile charge carriers.

A high melting point does not guarantee conductivity. Silicon and many ionic solids are strong lattices but lack freely moving charge carriers in the solid state.