Covalent molecular solids (like sugar) and covalent network solids (like diamond) have similar bonds and bond strengths. however, molecular solids are brittle and network solids are very strong and durable. explain the difference.

Covalent molecular solids (like sugar): No intermolecular covalent bonds

Covalent network solids (like diamond) : Intermolecular covalent interactions are present.

Explanation:

Covalent moleuclar solids are the solids which have "intera-molecular" covalent bonds i.e the covalent bonds exist between two atoms within the same molecule. The intermolecular bonds are not covalent. They are some weak intermolecular interactions like hydrogen bonds or disperison forces.

In case of covalent network solids, the intermolecular interactions are also strong covalent bonds. Thus they give a more strength and firmness to the compound or solid.