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Jai Ganesh

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Registered: 2005-06-28

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Metal

Metal

Gist

What is a Metal ? Metals. Metals are opaque, lustrous elements that are good conductors of heat and electricity. Most metals are malleable and ductile and are, in general, denser than the other elemental substances.

Summary

A Metal is any of a class of substances characterized by high electrical and thermal conductivity as well as by malleability, ductility, and high reflectivity of light.

Approximately three-quarters of all known chemical elements are metals. The most abundant varieties in the Earth’s crust are aluminum, iron, calcium, sodium, potassium, and magnesium. The vast majority of metals are found in ores (mineral-bearing substances), but a few such as copper, gold, platinum, and silver frequently occur in the free state because they do not readily react with other elements.

Metals are usually crystalline solids. In most cases, they have a relatively simple crystal structure distinguished by a close packing of atoms and a high degree of symmetry. Typically, the atoms of metals contain less than half the full complement of electrons in their outermost shell. Because of this characteristic, metals tend not to form compounds with each other. They do, however, combine more readily with nonmetals (e.g., oxygen and sulfur), which generally have more than half the maximum number of valence electrons. Metals differ widely in their chemical reactivity. The most reactive include lithium, potassium, and radium, whereas those of low reactivity are gold, silver, palladium, and platinum.

The high electrical and thermal conductivities of the simple metals (i.e., the non-transition metals of the periodic table) are best explained by reference to the free-electron theory. According to this concept, the individual atoms in such metals have lost their valence electrons to the entire solid, and these free electrons that give rise to conductivity move as a group throughout the solid. In the case of the more complex metals (i.e., the transition elements), conductivities are better explained by the band theory, which takes into account not only the presence of free electrons but also their interaction with so-called d electrons.

The mechanical properties of metals, such as hardness, ability to resist repeated stressing (fatigue strength), ductility, and malleability, are often attributed to defects or imperfections in their crystal structure. The absence of a layer of atoms in its densely packed structure, for example, enables a metal to deform plastically, and prevents it from being brittle.

Details

A metal (from Ancient Greek (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 are typically ductile (can be drawn into wires) and malleable (they can be hammered into thin sheets). These properties are the result of the metallic bond between the atoms or molecules of the metal.

A metal may be a chemical element such as iron; an alloy such as stainless steel; or a molecular compound such as polymeric sulfur nitride.

In physics, a metal is generally regarded as any substance capable of conducting electricity at a temperature of absolute zero. Many elements and compounds that are not normally classified as metals become metallic under high pressures. For example, the nonmetal iodine gradually becomes a metal at a pressure of between 40 and 170 thousand times atmospheric pressure. Equally, some materials regarded as metals can become nonmetals. Sodium, for example, becomes a nonmetal at pressure of just under two million times atmospheric pressure, though at even higher pressures it is expected to become a metal again.

In chemistry, two elements that would otherwise qualify (in physics) as brittle metals—math and antimony—are commonly instead recognised as metalloids due to their chemistry (predominantly non-metallic for math, and balanced between metallicity and nonmetallicity for antimony). Around 95 of the 118 elements in the periodic table are metals (or are likely to be such). 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.

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. 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. A star fuses lighter atoms, mostly hydrogen and helium, into heavier atoms over its lifetime. Used in that sense, the metallicity of an astronomical object is the proportion of its matter made up of the heavier chemical elements.

Metals, as chemical elements, comprise 25% of the Earth's crust and are present in many aspects of modern life. The strength and resilience of some metals has led to their frequent use in, for example, high-rise building and bridge construction, as well as most vehicles, many home appliances, tools, pipes, and railroad tracks. Precious metals were historically used as coinage, but in the modern era, coinage metals have extended to at least 23 of the chemical elements.

The history of refined metals is thought to begin with the use of copper about 11,000 years ago. Gold, silver, iron (as meteoric iron), lead, and brass were likewise in use before the first known appearance of bronze in the fifth millennium BCE. Subsequent developments include the production of early forms of steel; the discovery of sodium—the first light metal—in 1809; the rise of modern alloy steels; and, since the end of World War II, the development of more sophisticated alloys.

Additional Information

Metals are a class of elements characterized by a tendency to give up electrons. Metals are good thermal and electrical conductors. At room temperature and normal atmospheric pressure, metals tend to be solids - except for mercury, which is a liquid. Metals are usually ductile, malleable, shiny, and can form alloys with other metals.  Metals are tremendously important to a high energy society: they transport electricity in the electrical grid, and provide many services. Various manufacturing processes around the world uses more than 3 gigatonnes of metal every year. Industry uses more than 30 different metals, with the most used being iron (the biggest component of steel), chromium and manganese (both are added in small quantities to iron to make different types of steel), aluminum,and copper.

Generally, metallic elements are not found as isolated atoms, and instead group together into larger structures. These structures resemble large, extended sheets with a repeating pattern in how the atoms group together. It is this sheet-like structure that makes metals so useful, allowing them to be pressed into sheets that are used in building cars, containers, and even jewelry. In general, metallic atomic structures are highly organized and layers of these atoms stack to form a three-dimensional solid.

Unlike certain diatomic molecules - like molecular hydrogen or molecular oxygen - metals stay together because inside of the metal the electrons flow freely in a type of "electron sea" instead of sharing electrons between atoms. These electrons float freely around the nuclei inside of the metal. This free flowing "electron sea" explains why metals conduct electricity so well, as the movement of electrons produces an electric current, and there are so many electrons that are free to move inside of metals.

Energy Use for Metals

Metals are necessary to maintain society's modern standard of living. This demand contributes to energy demand because the extraction and processing of metals is extremely energy intensive. A significant fraction of the world's energy supply go into the mining of metals and turning them into useful products in the modern world. Since there is so much energy involved in metal processing, they have an incredible amount of embedded energy. Aluminum, in particular, requires a significant amount of energy to extract and process. When countries are modernizing their economies - in places like BRIC or N11 countries - large amounts of energy are invested to obtain metal for rapidly increasing infrastructure.

Metals account for roughly 20% of industrial energy use and 7% of all primary energy use in the world.

Metals are a Resource

Metals are an important resource for the world today with almost countless applications. The most widely used metal is also the least expensive: iron. Iron is the main component of steel. The electrical grid couldn't exist without copper and steel. In fact all areas of electricity production and distribution require metal, from turbines used to transform mechanical energy into electricity to the distribution stations that bring electricity to homes.

In addition to the electrical grid, metals are a principle component building construction (often in the form of steel reinforcement for concrete). Most vehicles are made from metal, from automobiles to airplanes. Common household appliances and electronic devices also use a significant amount of different metals as well. As technology advances, the number of elements used in society (including metals) increases.

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