The intermolecular forces are always weaker than the intramolecular forces.

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At its heart, this tests the idea that bonds inside a molecule are typically much stronger than the attractions between molecules. Intramolecular forces are the bonds that hold atoms together within a molecule—covalent bonds and, in some cases, ionic bonds within a compound. These require a relatively large amount of energy to break, often hundreds of kilojoules per mole for covalent bonds. Intermolecular forces are the attractions between separate molecules—hydrogen bonds, dipole–dipole interactions, and London dispersion forces. Their energies are much smaller, usually tens of kilojoules per mole or less.

A helpful way to see this is to compare the same substance in its liquid or solid form with its own internal bonds intact. In water, for example, the strong O–H covalent bonds stay within each molecule, while the weaker hydrogen bonds form between different water molecules. To separate water into individual molecules, you mainly break those intermolecular interactions; to break a single water molecule into atoms, you’d have to break the strong intramolecular O–H bonds. This difference in bond strength underpins why intermolecular forces are weaker than intramolecular forces overall.

There are edge cases in certain materials, but as a general rule the statement holds true: intramolecular bonds are stronger, and intermolecular forces are weaker.