Metals, as chemical elements, comprise 25% of the Earth's crust and are present in many aspects of modern life. Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements. A star fuses lighter atoms, mostly hydrogen and helium, into heavier atoms over its lifetime. In this sense the first four 'metals' collecting in stellar cores through nucleosynthesis are carbon, nitrogen, oxygen, and neon, all of which are strictly non-metals in chemistry. In astrophysics the term 'metal' is cast more widely to refer to all chemical elements in a star that are heavier than helium, and not just traditional metals. The number is inexact as the boundaries between metals, nonmetals, and metalloids fluctuate slightly due to a lack of universally accepted definitions of the categories involved. Around 95 of the 118 elements in the periodic table are metals (or are likely to be such). In chemistry, two elements that would otherwise qualify (in physics) as brittle metals- arsenic and antimony-are commonly instead recognised as metalloids due to their chemistry (predominantly non-metallic for arsenic, and balanced between metallicity and nonmetallicity for antimony). Sodium, for example, becomes a nonmetal at pressure of just under two million times atmospheric pressure. Equally, some materials regarded as metals can become nonmetals. For example, the nonmetal iodine gradually becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure. Many elements and compounds that are not normally classified as metals become metallic under high pressures. In physics, a metal is generally regarded as any substance capable of conducting electricity at a temperature of absolute zero.

These properties are the result of the metallic bond between the atoms or molecules of the metal.Ī metal may be a chemical element such as iron an alloy such as stainless steel or a molecular compound such as polymeric sulfur nitride.

Metals are typically ductile (can be drawn into wires) and malleable (they can be hammered into thin sheets). A metal (from Greek μέταλλον métallon, 'mine, quarry, metal') is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well.

Metals lost to time