What characterizes covalent solids?

Covalent solids are characterized primarily by their structure, where they appear as one large molecule interconnected by a network of covalent bonds. This means that the entire solid is formed from a continuous three-dimensional network of atoms that are bonded together via strong covalent bonds. Because of this network structure, they often have high melting and boiling points and are typically very hard materials.

This unique characteristic of forming a continuous lattice is fundamental to understanding covalent solids. Unlike ionic solids, which are made up of ions held together by ionic bonds, or metallic solids, which consist solely of metal atoms that share a sea of electrons, covalent solids manifest a distinct behavior owing to their networked atomic structure. They exhibit properties such as durability and stability due to the strength and directionality of the covalent bonds within the structure.

The other options describe characteristics that do not apply to covalent solids. For example, forming strong ionic bonds describes ionic compounds instead. Similarly, containing only metal atoms refers to metallic solids, and a fixed, crystalline structure is more typical of a broader range of solids, not specifically covalent ones. The key factor in identifying covalent solids lies in their extensive bonding network, which defines their overall properties.