Which of the following compounds are molecular, and which have an extended three-dimensional structure? (a) B2H6 (b) KAlSi3O8 (c) SO3 (d) GeCl4

Molecular compounds are formed when two or more nonmetals bond together through covalent bonds, sharing electrons. These compounds typically exist as discrete molecules and have relatively low melting and boiling points. Examples include water (H2O) and sulfur trioxide (SO3), which are characterized by their molecular structure and distinct molecular properties.

Ionic compounds consist of positively and negatively charged ions held together by strong electrostatic forces known as ionic bonds. These compounds usually form a crystalline lattice structure, resulting in high melting and boiling points. An example is potassium aluminum silicate (KAlSi3O8), which has a three-dimensional extended structure due to the arrangement of its ions.

Covalent network solids are materials where atoms are bonded by a continuous network of covalent bonds, resulting in a rigid structure. These solids exhibit high melting points and are typically hard and insoluble. An example is germanium tetrachloride (GeCl4), which can form a network structure under certain conditions, contrasting with molecular compounds that consist of individual molecules.