A metal is an element that readily forms cations and bonds ionically. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. Elements on this line are metalloids, sometimes called semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals.
Metals have certain characteristic physical properties: they are usually shiny, have a high density, are ductile and malleable, usually have a high melting point, are usually hard, and conduct electricity and heat well. These properties are mainly because each atom exerts only a loose hold on its outermost electrons (valence electrons); thus, the valence electrons form a sort of sea around the atoms. Most metals are chemically stable, with the notable exception of the alkali metals and alkaline earth metals, found in the leftmost two groups of the periodic table.
Nonmetals are more abundant in nature than are metals, but metals in fact constitute most of the periodic table. Some well-known metals are aluminium, copper, gold, iron, lead, silver, titanium, uranium, and zinc.
An alloy is a mixture with metallic properties that contains at least one metal element. Examples of alloys are steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), and duralumin (aluminium and copper). Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.
The oxides of metals are basic; those of nonmetals are acidic. The allotropes of metals tend to be lustrous, ductile, malleable, and good conductorss, while nonmetals generally speaking are brittle (for solid nonmetals), lack luster, and are insulators.
In astronomy, a metal is any element other than hydrogen or helium. This distinction is significant because hydrogen and helium (together with trace amounts of lithium) are the only elements that occur naturally without the fusion activity of stars. Thus, the metallicity of a galaxy or other object is an indication of past stellar activity.
See also: Metal-rich
Metal is also one of the Chinese five elements, though in that context the word has a much less literal meaning.
Road metal is the name of stone chippings mixed with tar to form the road surfacing material tarmac. A road of such material is called a "metalled road" in British usage. The word metal is derived from the Latin metallum, which means both "mine" and "quarry", hence the roadbuilding terminology.