Covalent-network solids are characterized by which description?

• A. Ionic lattice with charged ions.
• B. Atoms connected by covalent bonds; the intermolecular forces are covalent bonds as well. Very hard; Very high melting points; Poor conductors.
• C. Malleable metals with sea of electrons.
• D. Molecular solids with weak dispersion forces only.

Answer: (B)

Covalent-network solids form a continuous framework where atoms are linked by covalent bonds throughout the entire crystal, not just within small molecules. This extended bonding means that breaking the solid requires severing many strong covalent bonds, which is why these materials are extremely hard and have very high melting points. Since the electrons are largely tied up in those bonds and there are few free carriers, their electrical conductivity is poor. The other descriptions point to different bonding types—ionic lattices, metallic bonding, or molecular solids held together by weak van der Waals forces—and don't capture the networked, all-encompassing covalent bonding that defines covalent-network solids.