The Full Wiki

Metal: Wikis

  
  
  
  
  
  

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.

Did you know ...


More interesting facts on Metal

Include this on your site/blog:

Encyclopedia

From Wikipedia, the free encyclopedia

Metals
Alkali metals
Lithium, Sodium, Potassium
Rubidium, Caesium, Francium
Alkaline earth metals
Beryllium, Magnesium, Calcium
Strontium, Barium, Radium
Transition metals
Zinc, Molybdenum, Cadmium
Scandium, Titanium, Vanadium
Chromium, Manganese, Iron
Cobalt, Nickel, Copper
Yttrium, Zirconium, Niobium
Technetium, Ruthenium, Rhodium
Palladium, Silver, Hafnium
Tantalum, Tungsten, Rhenium
Osmium, Iridium, Platinum
Gold, Mercury, Rutherfordium,
Dubnium, Seaborgium, Bohrium,
Hassium, Meitnerium,
Darmstadtium, Roentgenium, Ununbium
Post-transition metals
Aluminium, Gallium, Indium
Tin, Thallium, Lead, Bismuth
Ununtrium, Ununquadium
Ununpentium, Ununhexium
Lanthanoids
Lanthanum, Cerium, Praseodymium
Neodymium, Promethium, Samarium
Europium, Gadolinium, Terbium
Dysprosium, Holmium, Erbium
Thulium, Ytterbium, Lutetium
Actinoids
Actinium, Thorium, Protactinium
Uranium, Neptunium, Plutonium
Americium, Curium, Berkelium
Californium, Einsteinium, Fermium
Mendelevium, Nobelium, Lawrencium

A metal is a chemical element that is a good conductor of both electricity and heat and forms cations and ionic bonds with non-metals. In chemistry, a metal (Ancient Greek métallon, μέταλλον) is an element, compound, or alloy characterized by high electrical conductivity. In a metal, atoms readily lose electrons to form positive ions (cations). Those ions are surrounded by delocalized electrons, which are responsible for the conductivity. The solid thus produced is held by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds.[1]

Contents

Definition

Metals are sometimes described as an arrangement of positive ions surrounded by a cloud of delocalized electrons. They are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and non-metals.

Metals occupy the bulk of the periodic table, while non-metallic elements can only be found on the right-hand-side of the Periodic Table of the Elements. A diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semiconductors. This is due to the fact that these elements exhibit electrical properties common to both conductors and insulators. Elements to the lower left of this division line are called metals, while elements to the upper right of the division line are called non-metals.

An alternative definition of metal refers to the band theory. If one fills the energy bands of a material with available electrons and ends up with a top band partly filled then the material is a metal. 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 gray reflectiveness (luster) of elemental metals.

Properties

Chemical

Metals are usually inclined to form cations through electron loss,[1] reacting with oxygen in the air to form oxides over changing timescales (iron rusts over years, while potassium burns in seconds). Examples:

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

The transition metals (such as iron, copper, zinc, and nickel) take much longer to oxidize. Others, like palladium, platinum and gold, do not react with the atmosphere at all. Some metals form a barrier layer of oxide on their surface which cannot be penetrated by further oxygen molecules and thus retain their shiny appearance and good conductivity for many decades (like aluminium, some steels, and titanium). The oxides of metals are generally basic, as opposed to those of nonmetals, which are acidic.

Painting, anodizing or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion.

Physical

Gallium crystals

Metals in general have high electrical conductivity, thermal conductivity, luster and density, and the ability to be deformed under stress without cleaving.[1] While there are several metals that have low density, hardness, and melting points, these (the alkali and alkaline earth metals) are extremely reactive, and are rarely encountered in their elemental, metallic form. Optically speaking, metals are opaque, shiny and lustrous. This is due to the fact that visible lightwaves are not readily transmitted through the bulk of their microstructure. The large number of free electrons in any typical metallic solid (element or alloy) is responsible for the fact that they can never be categorized as transparent materials.

The majority of metals have higher densities than the majority of nonmetals.[1] Nonetheless, there is wide variation in the densities of metals; lithium is the least dense solid element and osmium is the densest. The metals of groups I A and II A are referred to as the light metals because they are exceptions to this generalization[1]. The high density of most metals is due to the tightly packed crystal lattice of the metallic structure. The strength of metallic bonds for different metals reaches a maximum around the center of the transition series, as those elements have large amounts of delocalized electrons in a metallic bond. However, other factors (such as atomic radius, nuclear charge, number of bonding orbitals, overlap of orbital energies, and crystal form) are involved as well.[1]

Electrical

The electrical and thermal conductivity of metals originate from the fact that in the metallic bond, the outer electrons of the metal atoms form a gas of nearly free electrons, moving as an electron gas in a background of positive charge formed by the ion cores. Good mathematical predictions for electrical conductivity, as well as the electrons' contribution to the heat capacity and heat conductivity of metals can be calculated from 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 crystals. The most important consequence of the periodic potential is the formation of a small band gap at the boundary of the Brillouin zone. Mathematically, the potential of the ion cores can be treated by various models, the simplest being the nearly free electron model.

Mechanical

Mechanical properties of metals include their ductility, which is largely due to their inherent capacity for plastic deformation. Thus, elasticity in metals can be described by Hooke's Law for restoring forces, where the stress is linearly proportional to the strain. Larger forces in excess of the elastic limit may cause a permanent (irreversible) deformation of the object. This is what is known in the literature as plastic deformation -- or plasticity. This irreversible change in atomic arrangement may occur as a result of either (or both) of the following factors:

Hot metal work from a blacksmith.

In the former case, the applied force may be tensile (pulling) force, compressive (pushing) force, shear, bending or torsion (twisting) forces. In the latter case, the most significant factor which is determined by the temperature is the mobility of the structural defects such as grain boundaries, point vacancies, line and screw dislocations, stacking faults and twins in both crystalline and non-crystalline solids. The movement or displacement of such mobile defects is thermally activated, and thus limited by the rate of atomic diffusion.

Viscous flow near grain boundaries, for example, can give rise to internal slip, creep and fatigue in metals. It can also contribute to significant changes in the microstructure like grain growth and localized densification due to the elimination of intergranular porosity. Screw dislocations may slip in the direction of any lattice plane containing the dislocation, while the principal driving force for "dislocation climb" is the movement or diffusion of vacancies through a crystal lattice.

In addition, the nondirectional nature of metallic bonding is also thought to contribute significantly to the ductility of most metallic solids. When the planes of an ionic bond slide past one another, the resultant change in location shifts ions of the same charge into close proximity, resulting in the cleavage of the crystal. Such shift is not observed in covalently bonded crystals where fracture and crystal fragmentation occurs. [2]

Alloys

An alloy is a mixture of two or more elements in solid solution in which the major component is a metal. Most pure metals are either too soft, brittle or chemically reactive for practical use. Combining different ratios of metals as alloys modifies the properties of pure metals to produce desirable characteristics. The aim of making alloys is generally to make them less brittle, harder, resistant to corrosion, or have a more desirable color and luster. Of all the metallic alloys in use today, the alloys of iron (steel, stainless steel, cast iron, tool steel, alloy steel) make up the largest proportion both by quantity and commercial value. Iron alloyed with various proportions of carbon gives low, mid and high carbon steels, with increasing carbon levels reducing ductility and toughness. The addition of silicon will produce cast irons, while the addition of chromium, nickel and molybdenum to carbon steels (more than 10%) results in stainless steels.

Other significant metallic alloys are those of aluminium, titanium, copper and magnesium. Copper alloys have been known since the Bronze Age, and have many applications today, most importantly in electrical wiring. while the alloys of the other three metals have been developed relatively recently - chemical reactivity of these metals, requires modern electrolytic extraction processes. The alloys of aluminium, titanium and magnesium are also known and valued for their high strength-to-weight ratios and, in the case of magnesium, for the ability to provide electromagnetic shielding. These materials are ideal for situations where high strength-to-weight ratios are more important than bulk cost, such as in aerospace and in certain automotive applications.

Alloys specially designed for highly demanding applications, such as jet engines, may contain more than ten elements.

Categories

Base metal

In chemistry, the term 'base metal' is used informally to refer to a metal that oxidizes or corrodes relatively easily, and reacts variably with dilute hydrochloric acid (HCl) to form hydrogen. Examples include iron, nickel, lead and zinc. 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 alchemy, a base metal was a common and inexpensive metal, as opposed to precious metals, mainly gold and 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

The term "ferrous" is derived from the Latin word meaning "containing iron". This can include pure iron, such as wrought iron, or an alloy such as steel. Ferrous metals are often magnetic, but not exclusively.

Noble metal

Noble metals are metals that are resistant to corrosion or oxidation, unlike most base metals. They tend to be precious metals, often due to perceived rarity. Examples include tantalum, gold, platinum, silver and rhodium.

Precious metal

A gold nugget

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

Chemically, the precious metals are less reactive than most elements, have high luster and high electrical conductivity. Historically, precious metals were important as currency, but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum and palladium each have an ISO 4217 currency code. The best-known precious metals are gold and silver. While both have industrial uses, they are better known for their uses in art, jewelry, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded. Plutonium and 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

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 extracted, usually by chemical or electrolytic reduction. Pyrometallurgy uses high temperatures to convert ore into raw metals, while hydrometallurgy employs aqueous chemistry for the same purpose. The methods used depend on the metal and their contaminants.

When a metal ore is an ionic compound of that metal and a non-metal, the ore must usually be smelted — heated with a reducing agent — to extract the pure metal. Many common metals, such as iron, are smelted using carbon as a reducing agent. Some metals, such as aluminium and sodium, have no commercially practical reducing agent, and are extracted using electrolysis instead.[3]

Sulfide ores are not reduced directly to the metal but are roasted in air to convert them to oxides.

Metallurgy

Metallurgy is 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.

The two most commonly used structural metals, iron and aluminium, are also the most abundant metals in the Earth's crust.[4]

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 uranium and plutonium are used in nuclear power plants to produce energy via nuclear fission. Mercury is a liquid at room temperature and is used in switches to complete a circuit when it flows over the switch contacts. Shape memory alloy is used for applications such as pipes, fasteners and vascular stents.

Trade

Metal and ore imports in 2005

The World Bank reports that China was the top importer of ores and metals in 2005 followed by the U.S.A. and Japan.[5]

Astronomy

In the specialized usage of astronomy and astrophysics, the term "metal" is often used to refer to any element other than hydrogen or helium, including substances as chemically non-metallic as neon, fluorine, and oxygen. Nearly all the hydrogen and helium in the Universe was created in Big Bang nucleosynthesis, whereas all the "metals" were produced by nucleosynthesis in stars or supernovae. The Sun and the Milky Way Galaxy are composed of roughly 74% hydrogen, 24% helium, and 2% "metals" (the rest of the elements; atomic numbers 3-118) by mass.[6]

See also

References

  1. ^ a b c d e f Mortimer, Charles E. (1975). Chemistry: A Conceptual Approach (3rd ed.). New York:: D. Van Nostrad Company.  
  2. ^ Ductility - strength of materials
  3. ^ "Los Alamos National Laboratory – Sodium". http://periodic.lanl.gov/elements/11.html. Retrieved 2007-06-08.  
  4. ^ Frank Kreith and Yogi Goswami, eds. (2004). The CRC Handbook of Mechanical Engineering, 2nd edition. Boca Raton. p. 12-2.
  5. ^ Structure of merchandise imports
  6. ^ Sparke, Linda S.; Gallagher, John S. (2000), Galaxies in the Universe (1 ed.), Cambridge University Press, pp. 8, ISBN 0521592410  

External links


1911 encyclopedia

Up to date as of January 14, 2010
(Redirected to Database error article)

From LoveToKnow 1911

(There is currently no text in this page)


Wiktionary

Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

See also metal

German

Wikipedia-logo.png
German Wikipedia has an article on:
Metal

Wikipedia de

Noun

Metal m.

  1. heavy metal (music)

Simple English

See also: Heavy metal music

A group of elements in the periodic table is called metals. These elements usually have the following properties:

  1. They can conduct electricity and heat
  2. They can be formed easily
  3. They have a shiny appearance.

Most metals are solid, at room temperature, but this does not have to be the case. Mercury is liquid. Alloys are mixtures, where at least one part of the mixure is a metal. Examples for metals are aluminium, copper, iron, tin, gold, lead, silver, titanium, uranium, and zinc. Well-known alloys include bronze and steel.

The study of metals is called metallurgy.

Contents

The ways that metals are alike (properties of metals)

Most metals are hard, shiny, they feel heavy (dense) and they melt only when they are very hot. Lumps of metal will make a bell-like sound when they are hit with something heavy (they are sonorous). Heat and electricity can easily pass through a metal (it is conductive). A lump of metal can be beaten into a thin sheet (it is malleable) or can be pulled into thin wires (it is ductile). Metal is hard to pull apart (it has a high tensile strength) or smash (it has a high compressive strength). If you push on a long, thin piece of metal, it will bend, not break (it is elastic).

Not all metals have these properties. Lead, for instance, is very soft, and heat and electricity do not pass through iron as well as they do through copper.

Use of metals

[[File:|thumb|right|A bridge in Russia made of metal, probably iron or steel.]] Metals are very useful to people. They are used to make tools because they can be strong and easy to shape. Iron and steel have been used to make bridges, buildings, or ships.

Some metals are used to make items like coins because they are hard and will not wear away quickly. For example copper (which is shiny and red in color), aluminum (which is shiny and white), gold (which is yellow and shiny) , and silver and nickel (also white and shiny).

Some metals, like steel, can be made sharp and stay sharp, so they can be used to make knives, axes or razors.

Rare metals with high value, like gold, silver and platinum are often used to make jewelery. Metals are also used to make fasteners and screws. Pots used for cooking can be made from copper, aluminum, steel or iron. Lead is very heavy and dense and can be used as ballast in boats to stop them from turning over, or to protect people from ionizing radiation.

Alloys of metals

Many things that are made of metals may, in fact, be made of mixtures of at least one metal with either other metals, or with non-metals. These mixtures are called alloys. Some common alloys are:

People first began making things from metal over 9000 years ago, when they discovered how to get copper from its ore. They then learned how to make a harder alloy, bronze, by adding tin to the copper. About 3000 years ago, they discovered iron. By adding small amounts of carbon to iron, they found that they could make a particularly useful alloy – steel.

Metals in chemistry

In chemistry, metal is a word for a group of chemical elements that have certain properties. It is easy for the atoms of a metal to lose an electron and become positive ions, or cations. In this way, metals are not like the other two kinds of elements - the nonmetals and the metalloids.

On the periodic table, we can draw a straight line from the element boron (symbol B) to the element polonium (symbol Po). The elements that this line passes through are the metalloids. The elements that are above and to the right of this line are the nonmetals. The rest of the elements are the metals.

Most of the properties of metals are because the atoms in the metal do not hold onto their electrons very tightly. Each atom is separated from the others by a thin layer of valence electrons. However, some metals are different. An example is the metal sodium. It is soft, melts at a low temperature, and is so light, it floats on water. People should not try this though, because another property of sodium is that it explodes when it touches water.

Most metals are chemically stable, and do not react easily. (Some of the metals do react. These are the alkali metals like sodium (symbol Na) and the alkaline earth metals like calcium (symbol Ca).) When metals do react, they often react with oxygen. The oxides of metals are basic. The oxides of nonmetals are acidic. However, most of the elements on the periodic table are metals.

Compounds, which have metal atoms combined with other atoms to make molecules, are probably the most common things on the Earth. For example, common salt is a compound of sodium.

Metals in history

File:Native
A lump of pure copper found as native copper

The use of metals is said to be the thing that makes people different from animals. Before they used metals, people made tools from stones, wood, and animal bones. This is now called the Stone Age.

No-one knows when the first metal was found and used. It was probably what is called native copper, which is sometimes found in large lumps on the ground. People learned to make this into copper tools and other things, although, for a metal, it is quite soft. When it was melted over fire, people learned how to make an alloy called bronze, which is much harder and stronger than copper. People made knives and weapons from bronze. This time in human history, after about 3300 BC is often called the Bronze Age, that is, the time of bronze tools and weapons.

Around the year 1200 BC some people learned to make iron tools and weapons. These were even harder and stronger than bronze and this was an advantage in war. The time of iron tools and weapons is now called the Iron Age . Metals have been very important in human history and civilization. Iron and steel were important in the making of machines. Gold and silver were used as money in order to allow people to trade, that is, exchange goods and services over long distances.

Many people thought that finding metals was a way to get rich. There have been many times when gold was found and people moved quickly in large numbers to those places for example, Central and South America after the year 1500, and many places after the year 1800 (the United States of America, Canada, Australia, New Zealand and South Africa). These are often called Gold Rushes.

Metals in astronomy

In astronomy, a metal is any element other than hydrogen or helium. This is because these two elements (and sometimes lithium) are the only ones that form outside stars. In the sky, a telescope can see the signs of metals and then the astronomer knows that there are stars.

Other pages








Got something to say? Make a comment.
Your name
Your email address
Message