Usually water insoluble. Do not conduct electric current. M.P. and b.p. depend upon whether molecular or macromolecular. Molecular solids have covalent bonds within the molecule only. When you come to the end of the molecule, no chemical bond exists between that point and the next molecule.
Molecular substances are the only ones with low boiling points.
They also have low m.p. Covalent macromolecular substances have high m.p. and b.p., and some are among the highest melting substances. CCl4is covalent molecular, consists of CCl4 molecules. The low m.p. The high m.p. of SiO2 is typical of covalent macromolecular solids.