Covalent forces are very strong intermolecular forces. In fact, we can say they are the strongest. This is because several big and giant molecules have covalent bonds holding their molecules together. A good example of this is the buckministerfullerence molecule which contains carbon atom to the order of 60 carbon atoms. It is a very giant molecule and it is covalent bond that is holding the molecules together
The strongest substance in the world is diamond. It is so strong that no other substance can cut it asides another diamond. As strong as it is, the molecule is held together by very strong intermolecular forces of covalent bonds which confers the strength it has on it
