04 Properties of Simple Covalent Molecules

Substances that consist of small molecules are usually gases or liquids that have relatively low melting points and boiling points.

These substances have only weak forces between the molecules (intermolecular forces). Little energy is needed to weaken or break these forces, therefore low melting and boiling points.

It is intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils.

The intermolecular forces increase with the size of the molecules, so larger molecules have higher melting and boiling points. Here's Dad to explain: