metal

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metal chemical element displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion , and the ability to conduct heat and electricity. The metals comprise about two thirds of the known elements (see periodic table ). Some metals, including copper, tin, iron, lead, gold, silver, and mercury, were known to the ancients; copper is probably the oldest known metal.

Physical Properties

Metals differ so widely in hardness, ductility (the potentiality of being drawn into wire), malleability, tensile strength, density, and melting point that a definite line of distinction between them and the nonmetals cannot be drawn. The hardest elemental metal is chromium; the softest, cesium. Copper, gold, platinum, and silver are especially ductile. Most metals are malleable; gold, silver, copper, tin, and aluminum are extremely so. Some metals exhibiting great tensile strength are copper, iron, and platinum. Three metals (lithium, potassium, and sodium) have densities of less than one gram per cubic centimeter at ordinary temperatures and are therefore lighter than water. Some heavy metals, beginning with the most dense, are osmium, iridium, platinum, gold, tungsten, uranium, tantalum, mercury, hafnium, lead, and silver.

For many industrial uses, the melting points of the metals are important. Tungsten fuses, or melts, only at extremely high temperatures (3,370°C.), while cesium has a melting point of 28.5°C. The best metallic conductor of electricity is silver. Copper, gold, and aluminum follow in the order named. All metals are relatively good conductors of heat; silver, copper, and aluminum are especially conductive. The radioactive metal uranium is used in reactor piles to generate steam and electric power. Plutonium, another radioactive element, is used in nuclear weapons and nuclear reactors as well as in pacemakers. Some of the radioactive metals not found in nature, e.g., fermium and seaborgium, are produced by nuclear bombardment.

Some elements, e.g., arsenic and antimony, exhibit both metallic and nonmetallic properties and are called metalloids. Furthermore, although all metals form crystals, this is also characteristic of certain nonmetals, e.g., carbon and sulfur.

Chemical Properties

Chemically, the metals differ from the nonmetals in that they form positive ions and basic oxides and hydroxides. Upon exposure to moist air, a great many undergo corrosion, i.e., enter into a chemical reaction; e.g., iron rusts when exposed to moist air, the oxygen of the atmosphere uniting with the metal to form the oxide of the metal. Aluminum and zinc do not appear to be affected, but in fact a thin coating of the oxide is formed almost at once, stopping further action and appearing unnoticeable because of its close resemblance to the metal. Tin, lead, and copper react slowly under ordinary conditions. Silver is affected by compounds such as sulfur dioxide and becomes tarnished when exposed to air containing them. The metals are combined with nonmetals in their salts, as in carbides, carbonates, chlorides, nitrates, phosphates, silicates, sulfides, and sulfates.

The Electromotive Series

On the basis of their ability to be oxidized, i.e., lose electrons, metals can be arranged in a list called the electromotive series , or replacement series. Metals toward the beginning of the series, like cesium and lithium, are more readily oxidized than those toward the end, like silver and gold. In general, a metal will replace any other metal, or hydrogen, in a compound that it precedes in the series, and under ordinary circumstances it will be replaced by any metal, or hydrogen, that it follows.

Metals in the Periodic Table

Metals fall into groups in the periodic table determined by similar arrangements of their orbital electrons and a consequent similarity in chemical properties. Groups of similar metals include the alkali metals (Group 1 in the periodic table), the alkaline-earth metals (Group 2 in the periodic table), and the rare-earth metals (the lanthanide and actinide series of Group 3). Most metals other than the alkali metals and the alkaline earth metals are called transition metals (see transition elements ). The oxidation states, or valence , of the metal ions vary from +1 for the alkali metals to as much as +7 for some transition metals.

Sources and Uses

Although a few metals occur uncombined in nature, the great majority are found combined in their ores . The separation of metals from their ores is called extractive metallurgy . Metals are mixed with each other in definite amounts to form alloys ; a mixture of mercury and another metal is called an amalgam . Bronze is an alloy of copper and tin, and brass contains copper and zinc. Steel is an alloy of iron and other metals with carbon added for hardness.

Since metals form positive ions readily, i.e., they donate their orbital electrons, they are used in chemistry as reducing agents (see oxidation and reduction ). Finely divided metals or their oxides are often used as surface catalysts . Iron and iron oxides catalyze the conversion of hydrogen and nitrogen to ammonia in the Haber process . Finely divided catalytic platinum or nickel is used in the hydrogenation of unsaturated oils. Metal ions orient electron-rich groups called ligands around themselves, forming complex ions . Metal ions are important in many biological functions, including enzyme and coenzyme action, nucleic acid synthesis, and transport across membranes.

For the uses of specific metals, see separate articles.

metal Element that is a good conductor of heat and electricity. Its atoms bond together within crystals in a unique way. Mixtures of such elements (alloys) are also metals. About three-quarters of known elements are metals. Most are hard, shiny materials that form oxides. Malleability and ductility are further metallic characteristics. Some metals have very high melting points and various high-temperature applications: tungsten, with the highest melting point of all at 3410°C (6170°F), is employed for incandescent-lamp filaments. Aluminium and iron are the two most abundant and useful metals. Titanium, although rarely seen as a metal, is more commonly distributed than the more familiar copper, zinc, and lead. Other metals of economic importance, because they undergo nuclear fission, are uranium and plutonium.

met·al / ˈmetl/ • n. 1. a solid material that is typically hard, shiny, malleable, fusible, and ductile, with good electrical and thermal conductivity (e.g., iron, gold, silver, copper, and aluminum, and alloys such as brass and steel): vessels made of ceramics or metal | being a metal, aluminum readily conducts heat. ∎  Heraldry gold and silver (as tinctures in blazoning). 2. Brit. (also road met·al) broken stone for use in making roads. 3. molten glass before it is blown or cast. 4. heavy metal or similar rock music. • v. (met·aled , met·al·ing ; chiefly Brit. met·alled, met·al·ling) [tr.] [usu. as adj.] (metaled) make out of or coat with metal: metaled key rings.

metal metals were traditionally divided into noble or precious metals (gold, silver, and platinum, which resist corrosion) and base or imperfect metals (such as lead). In heraldry, metal is used for the tinctures or (gold) and argent (silver).

Recorded from Middle English, the word comes via Old French or Latin, from Greek metallon ‘mine, quarry, metal’.

metal XIII. — (O)F. métal, † metail or its source L. metallum mine, quarry, metal — synon. Gr. métallon.
So metallic XVI. metalline XV. — F. Hence metallize XVI. See METTLE.

metal In astronomical terminology, any element heavier than hydrogen or helium. The abundance of such heavy elements in celestial objects is termed their metallicity.

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