Chemical element the elements, including consideration of their general physical and chemical properties, their states of matter under familiar conditions, their melting and boiling points, their densities, their crystal structures as solids, and their origins. Several terms are commonly used to characterize the general physical and chemical properties of the chemical elements. A first distinction is between metals, which readily conduct electricity, nonmetals, which do not, and a small group, (the "metalloids"), having intermediate properties and often behaving as semiconductors. A more refined classification is often shown in colored presentations of the periodic table. This system restricts the terms "metal" and "nonmetal"
Cobalt radial tires. In addition they are used as accelerators in polyester resin systems. Cobalt-based catalysts are used in reactions involving carbon monoxide. Cobalt is also a catalyst in the Fischer–Tropsch process for the hydrogenation of carbon monoxide into liquid fuels. Hydroformylation of alkenes often uses cobalt octacarbonyl as a catalyst, although it is often replaced by more efficient iridium- and rhodium-based catalysts, e.g. the Cativa process. The hydrodesulfurization of petroleum uses a catalyst derived from cobalt and molybdenum. This process helps to clean petroleum of sulfur impurities that interfere with the refining of liquid fuels. Before the 19th century, cobalt