Trends in Period Three of the Periodic Table

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Groups I, II and III are metals and so metallic bonding is used.

Group IV is a macromolecule and so has a very large melting point.

Groups V, VI, VII are molecules and so we rely on temporary dipole-dipole attractions.

Phosphorus is P₄ and so has a reasonably large temporary dipole.

Sulphur is S₈ and so has a very large temporary dipole.

Chlorine is Cl₂ and so has a fairly small temporary dipole.

Going to argon, we notice that it is formed of single atoms and so it has a very small temporary dipole.