Metal



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In chemistry, a metal (Greek: Metallon) is an semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals.

An alternative definition of metals is that they have overlapping valence bands in their electronic structure. This definition opens up the category for metallic polymers and other organic metals, which have been made by researchers and employed in high-tech devices. These synthetic materials often have the characteristic silvery-grey reflectiveness (luster) of elemental metals.

The traditional definition focuses on the bulk properties of metals. They tend to be lustrous, ductile, malleable, and good conductors of electricity, while nonmetals are generally brittle (if insulators.

Chemical properties

Most metals are chemically reactive, reacting with oxygen in the air to form oxides over changing timescales (for example iron periodic table. Examples:

4Na + O2 → 2Na2O (sodium oxide)
2Ca + O2 → 2CaO (calcium oxide)
4Al + 3O2 → 2Al2O3 (aluminium oxide)

The acidic), although this may be considered a rule of thumb, rather than a fact.

Painting or electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion.

Physical properties

 

Traditionally, metals have certain characteristic physical properties: they are usually shiny (they have metallic alkaline earth metals) are extremely reactive, and are rarely encountered in their elemental, metallic form.

The electrical and thermal conductivity of metals originate from the fact that in the free electron model, which does not take the detailed structure of the ion lattice into account.

When considering the exact band structure and binding energy of a metal, it is necessary to take into account the positive potential caused by the specific arrangement of the ion cores - which is periodic in nearly-free electron model.

Alloys

Main article: Alloy

An alloy is a mixture of two or more copper). Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.

Categories

Base metal

Main article: Base metal

In Copper is considered a base metal as it oxidizes relatively easily, although it does not react with HCl. It is commonly used in opposition to noble metal.

In silver. A longtime goal of the alchemists was the transmutation of base metals into precious metals.

In numismatics, coins used to derive their value primarily from the precious metal content. Most modern currencies are fiat currency, allowing the coins to be made of base metal.

Ferrous metal

Main article: Ferrous and non-ferrous metals

The term "ferrous" is derived from the latin word meaning "containing iron". This can include pure iron, such as magnetic, but not exclusively.

Noble metal

Main article: Noble metal

Noble metals are metals that are resistant to rhodium.

Precious metal

Main article: Precious metal

A precious metal is a rare metallic chemical element of high economic value.

Chemically, the precious metals are less uranium could also be considered precious metals.

The demand for precious metals is driven not only by their practical use, but also by their role as investments and a store of value. Palladium was, as of summer 2006, valued at a little under half the price of gold, and platinum at around twice that of gold. Silver is substantially less expensive than these metals, but is often traditionally considered a precious metal for its role in coinage and jewelry.

Extraction

Main articles: Ore and Mining

Metals are often extracted from the Earth by means of mining, resulting in ores that are relatively rich sources of the requisite elements. Ore is located by prospecting techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into surface mines, which are mined by excavation using heavy equipment, and subsurface mines.

Once the ore is mined, the metals must be hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.


Metallurgy

Main article: Metallurgy

Metallurgy w\s a domain of materials science that studies the physical and chemical behavior of metallic elements, their intermetallic compounds, and their mixtures, which are called alloys.

Applications

Some metals and metal alloys possess high structural strength per unit mass, making them useful materials for carrying large loads or resisting impact damage. Metal alloys can be engineered to have high resistance to shear, torque and deformation. However the same metal can also be vulnerable to fatigue damage through repeated use, or from sudden stress failure when a load capacity is exceeded. The strength and resilience of metals has led to their frequent use in high-rise building and bridge construction, as well as most vehicles, many appliances, tools, pipes, non-illuminated signs and railroad tracks.

Metals are good conductors, making them valuable in electrical appliances and for carrying an electric current over a distance with little energy lost. Electrical power grids rely on metal cables to distribute electricity. Home electrical systems, for the most part, are wired with copper wire for its good conducting properties.

The thermal conductivity of metal is useful for containers to heat materials over a flame. Metal is also used for heat sinks to protect sensitive equipment from overheating.

The high reflectivity of some metals is important in the construction of mirrors, including precision astronomical instruments. This last property can also make metallic jewelry aesthetically appealing.

Some metals have specialized uses; Radioactive metals such as stents. However they are very good at conducting electricity and heat.

Trade

  The World Bank reports that China was the top importer of ores and metals in 2005 followed by the U.S.A. and Japan.

Astronomy

Main article: Metallicity

In the specialised usage of astronomy and astrophysics, the term "metal" is often used to refer to any element other than oxygen. Because the temperatures of stellar bodies allow practically no solid or liquid matter, and little normal chemistry can exist at temperatures that break down almost all chemical bonds, the term "metal" refers to materials that result from the triple-helium process which are much scarcer than hydrogen and helium in stars in the main sequence.

See also
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Metal". A list of authors is available in Wikipedia.