Classify each of the following statements as true or false: (a) Although both molecular solids and covalent-network solids have covalent bonds, the melting points of molecular solids are much lower because their covalent bonds are much weaker. (b) Other factors being equal, highly symmetric molecules tend to form solids with higher melting points than asymmetrically shaped molecules.

We need to determine if it's true that molecular solids have lower melting points because their covalent bonds are much weaker than those in covalent-network solids. Molecular solids are made of molecules held together with forces such as van der Waals, hydrogen bonding, or dipole-dipole interactions. Covalent-network solids, on the other hand, consist of a giant framework of covalently bonded atoms, forming a continuous network. The covalent bonds themselves are actually of similar strengths in both molecular solids and covalent-network solids. However, the key difference lies in the forces between the molecules, which are weaker in molecular solids. While the covalent bonds are not the cause of the lower melting points of molecular solids, the result is still true – molecular solids melt at lower temperatures than covalent-network solids.

Since the cause for lower melting points in molecular solids is due to weaker intermolecular forces rather than weaker covalent bonds, statement (a) is false.

We need to determine if it's true that, other factors being equal, highly symmetric molecules tend to form solids with higher melting points than asymmetrically shaped molecules. Higher symmetric molecules pack more efficiently into a crystalline lattice, leading to stronger intermolecular forces and therefore higher melting points compared to asymmetric molecules. Less efficient packing results in weaker forces between the molecules, leading to lower melting points when the overall molecular shape is not symmetrical.

Since highly symmetric molecules can pack more efficiently in a solid, leading to stronger intermolecular forces and higher melting points, statement (b) is true.