Solid materials have been conveniently grouped into three basic classifications: metals, ceramics, and polymers. Metallic materials are normally combinations of metallic elements. They have large numbers of electrons;that is,these electrons are not bound to particular atoms. are compounds between metallic and nonmetallic elements; they are most frequently oxides, nitrides, and carbides. include the familiar plastic and rubber materials. Many of them are organic compounds that are chemically based on carbon, hydrogen, and other nonmetallic elements