covalent bonds are strong within the molecule . But they have small intermolecular forces . WHY
Inter molecular forces are weaker than intramolecular forces.
Intermolecular forces are forces between different molecules and include things like London dispersion forces, Van der Waals forces and dipole-dipole interactions.
Intramolecular forces are stronger because they involve sharing of electrons for covalent bonds. This sharing of electrons gives each element of the bond an octet of electrons in the valence shell which is a highly stable electronic configuration.
By comparison, intermolecular interactions do not involve the sharing or transfer of electrons.
Hence, covalent bonds are stronger within atom but they have weak intermolecular forces.