Metal, a member of the largest class of chemical elements in the Periodic Table.

Approximately three-fourths of the elements are metals. Most metals are silvery in color, have a characteristic luster, and are solid (rather than liquid or gaseous). Most metals are also malleable (can be shaped with a hammer), ductile (can be drawn into a wire), and good conductors of both heat and electricity.

However, some nonmetals also have these physical properties, while some metals lack one or more of them. A few metals—such as antimony and bismuth—are brittle rather than malleable. Carbon, a nonmetal, conducts heat as well as indium does and better than bismuth. Mercury is not solid at room temperature. Iodine, a nonmetal, has a metallic luster. Copper and gold are not silvery in color. It is therefore difficult to make a clear-cut distinction, on the basis of physical properties, between metals and nonmetals.

Chemically, metals are elements that are electropositive; that is, they tend to form positive ions when they undergo electrolysis. However, hydrogen, a nonmetal, also has this characteristic.

The heaviest metal is iridium, which has a specific gravity of 22.6 (that is, it has 22.6 times the weight of an equal volume of water). Lithium, the lightest metal, has a specific gravity of 0.53. Gold is the most malleable and ductile of the metals. Silver is the best conductor of heat and electricity.

Metals are found mainly in ores, which are mined in a variety of ways. An ore may either have the metal present in elemental form or in compounds. The process used to refine the ore depends on the form and concentration of the metal.

Metals are used both in pure form and in alloys. An alloy is a mixture of a metal and other metals or nonmetals. (An alloy of mercury and another metal is called an amalgam.) Most metal tools, machines, ornaments, and structures are made of alloys.

Metals are essential to life. Calcium, which is necessary for strong and healthy bones, is a metal. Sodium, iron, and potassium, which are all metals, are also considered necessary to the body.

Some metals—gold, silver, lead, tin, mercury, iron, copper, and antimony—have been known since ancient times. Other metals, such as hafnium, rhenium, and lutetium, have been discovered in the 20th century.