Explain the melting points of period 3 elements.

Going from Na to Si, the melting point increases. This is because from Na-Al, the charge of the metal ion and the number of delocalised electrons increases so the strength of the metallic bonding increases as well. Hence the energy required to break bonds increases. Si exists as macromolecule with strong covalent bonds between the atoms which require a lot of energy to break. From phosphorus to argon, the melting points decrease in order of S₈ > P₄ > Cl₂ > Ar. I will show you on the whiteboard why sulphur has high melting point than phosphorus.