A network solid or covalent network solid is a chemical compound (or element) in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material. In a network solid there are no individual molecules, and the entire crystal may be considered a macromolecule. SiO2 is a network solid. Li2O and NaCl are ionic crystals. H2O is a covalent liquid and CO2 is a covalent gas.