Chemical classification

Solids are frequently classified according to their chemical bonding, Properties and structures:  

Molecular solids consist of discrete molecular units held by comparatively weak intermolecular forces.

Metallic solids contain atoms with high coordination numbers, bound by delocalized electrons which give metallic conduction.

Covalent or polymeric solids contain atoms bound by directional covalent bonds, giving comparatively low coordination numbers in a continuous one-, two- or three-dimensional network.

Ionic solids are bound through electrostatic attraction among anions and cations, with structures in which every anion is surrounded by cations and vice versa.

Even though these broad distinctions are useful, various solids depict a degree of intermediate character, or even various types of bonding concurrently. Metallic and covalent interactions both take place from overlapping atomic orbitals and the distinction in physical properties takes place from the energy distribution of electronic levels. The electronic and structures properties of elements depict a gradation in character at the metal-nonmetal borderline. An identical gradation is seen among ionic and covalent compounds as the electronegativity variations between two elements changes. Additionally, solids with predominantly ionic bonding among some atoms can also have covalent bonds between others.