In chemistry Chemistry (from Egyptian kēme , meaning "earth") is the science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions. It is a physical science for studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination,, a metal (Greek Greek , an Indo-European language native to the southern Balkan peninsula, is the language of the Greeks. It forms an independent branch within Indo-European. It has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical Ancient Greek literature: Metallo, Μέταλλο) is an element A chemical element is a pure chemical substance consisting of one type of atom distinguished by its atomic number, which is the number of protons in its nucleus. The term is also used to refer to a pure chemical substance composed of atoms with the same number of protons. Common examples of elements are iron, copper, silver, gold, hydrogen, carbon,, compound A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions and that have a unique and defined chemical structure. Chemical compounds consist of a fixed ratio of atoms that are held together in a defined spatial arrangement by chemical, or alloy An alloy is a partial or complete solid solution of one or more elements in a metallic matrix. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may be homogeneous in distribution depending on thermal history. Alloys usually have different properties from those of the characterized by high electrical conductivity Electrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity σ is defined as the ratio of the current density to the electric field strength :. In a metal, atoms readily lose electrons to form positive ions An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge (cations An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge); those ions are surrounded by delocalized electrons, which are responsible for the conductivity. The thus produced solid is held by electrostatic interactions between the ions and the electron cloud, which are called metallic bonds Metallic bonding is the electromagnetic interaction between delocalized electrons, called conduction electrons, and the metallic nuclei within metals. Understood as the sharing of "free" electrons among a lattice of positively-charged ions , metallic bonding is sometimes compared with that of molten salts; however, this simplistic view.^[1]

Definition

Metals are sometimes described as an arrangement of positive ions surrounded by a cloud of delocalized electrons The electron is a subatomic particle that carries a negative electric charge. It has no known substructure and is believed to be a point particle. Electrons participate in gravitational, electromagnetic and weak interactions. Like its rest mass and elementary charge, the intrinsic angular momentum of an electron has a constant value. In the. They are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids Metalloid, or semi metal is a term used in chemistry when classifying the chemical elements. On the basis of their general physical and chemical properties, nearly every element in the periodic table can be termed either a metal or a nonmetal. However, a few elements with intermediate properties are referred to as metalloids . They are sometimes and nonmetals. On the periodic table, a diagonal line drawn from boron Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a trivalent metalloid element which occurs abundantly in the evaporite ores borax and ulexite (B) to polonium Polonium is a chemical element with the symbol Po and atomic number 84, discovered in 1898 by Marie and Pierre Curie. A rare and highly radioactive metalloid, polonium is chemically similar to bismuth and tellurium, and it occurs in uranium ores. Polonium has been studied for possible use in heating spacecraft. It is unstable; all isotopes of (Po) separates the metals from the nonmetals. Most elements on this line are metalloids, sometimes called semi-metals However, the bottom of the conduction band is typically situated in a different part of momentum space than the top of the valence band. One could say that a semimetal is a semiconductor with a negative indirect bandgap, although they are seldom described in those terms; elements to the lower left are metals; elements to the upper right are nonmetals (see the periodic table showing the metals).

An alternative definition of metal refers to the band theory In solid-state physics, the electronic band structure of a solid describes ranges of energy that an electron is "forbidden" or "allowed" to have. It is due to the diffraction of the quantum mechanical electron waves in the periodic crystal lattice. The band structure of a material determines several characteristics, in. 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-grey reflectiveness (luster) of elemental metals.

Chemical properties

Metals are usually inclined to form cations An ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge through electron loss,^[1] reacting with oxygen in the air to form oxides An oxide is a chemical compound contaning at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon monoxide and carbon dioxide. Even materials that are over changing timescales (iron rusts Rust is a general term for a series of iron oxides, usually red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture. Several forms of rust are distinguishable visually and by spectroscopy, and form under different circumstances. Rust consists of hydrated iron oxides Fe2O3·nH2O and iron(III) oxide-hydroxide ( over years, while potassium Potassium is a chemical element. It has the symbol K (Latin: kalium, from Arabic: القَلْيَه‎ al-qalyah “plant ashes”, cf. Alkali from the same root), atomic number 19, and atomic mass 39.0983. Potassium was first isolated from potash. Elemental potassium is a soft silvery-white metallic alkali metal that oxidizes rapidly in air and burns in seconds). Examples:

4Na + O₂ → 2Na₂O (sodium oxide)

2Ca + O₂ → 2CaO (calcium oxide)

4Al + 3O₂ → 2Al₂O₃ (aluminium oxide)

The transition metals The first definition is simple and has traditionally been used. However, many interesting properties of the transition elements as a group are the result of their partly filled d subshells. Periodic trends in the d-block are less prevailing than in the rest of the periodic table. Going across a period, the valence doesn't change, so the electron (such as iron Iron is a chemical element with the symbol Fe (Latin: ferrum) and atomic number 26. Iron is a group 8 and period 4 element. Iron and iron alloys (steels) are by far the most common metals and the most common ferromagnetic materials in everyday use. Fresh iron surfaces are lustrous and silvery-grey in color, but oxidise in air to form a red or, copper Copper is a chemical element with the symbol Cu (Latin: cuprum) and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is rather soft and malleable and a freshly-exposed surface has a pinkish or peachy color. It is used as a thermal conductor, an electrical conductor, a building material, and a, zinc Zinc is a metallic chemical element with the symbol Zn and atomic number 30. It is a first-row transition metal in group 12 of the periodic table. Zinc is chemically similar to magnesium because its ion is of similar size and its only common oxidation state is +2. Zinc is the 24th most abundant element in the Earth's crust and has five stable, and nickel Nickel is a chemical element, with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. It is one of the four ferromagnetic elements at about room temperature. Its use has been traced as far back as 3500 BC, but it was first isolated and classified as a chemical element in 1751 by Axel) take much longer to oxidize. Others, like palladium Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. Palladium is a rare and lustrous silvery-white metal that was discovered in 1803 by William Hyde Wollaston, who named it after the asteroid Pallas, which in turn, was named after the epithet of the Greek goddess Athena, acquired by her when she slew Pallas, platinum Platinum is a chemical element with the chemical symbol Pt and an atomic number of 78. Its name is derived from the Spanish term platina del Pinto, which is literally translated into "little silver of the Pinto River." It is in Group 10 of the periodic table of elements. A dense, malleable, ductile, precious, gray-white transition metal, and gold Gold is a chemical element with the symbol Au (Latin: aurum) and an atomic number of 79. It has been a highly sought-after precious metal in jewelry, in sculpture, and for ornamentation since the beginning of recorded history. The metal occurs as nuggets or grains in rocks, in veins and in alluvial deposits. Gold is dense, soft, shiny and the most, do not react with the atmosphere at all. Some metals form a barrier layer of oxide An oxide is a chemical compound contaning at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon monoxide and carbon dioxide. Even materials that are 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 Aluminium ( ˌæljʊˈmɪniəm ) or aluminum ( /əˈluːmɪnəm/ (help·info), see spelling below) is a silvery white and ductile member of the boron group of chemical elements. It has the symbol Al; its atomic number is 13. It is not soluble in water under normal circumstances. Aluminium is the most abundant metal in the Earth's crust, and the, some steels Steel is an alloy consisting mostly of iron, with a carbon content between 0.2% and 2.14% by weight , depending on grade. Carbon is the most cost-effective alloying material for iron, but various other alloying elements are used such as manganese, chromium, vanadium, and tungsten. Carbon and other elements act as a hardening agent, preventing, and titanium Titanium is a chemical element with the symbol Ti and atomic number 22. Sometimes called the “space age metal”, it has a low density and is a strong, lustrous, corrosion-resistant (including to sea water, aqua regia and chlorine) transition metal with a silver color. Titanium can be alloyed with iron, aluminium, vanadium, molybdenum, among). The oxides An oxide is a chemical compound contaning at least one oxygen atom as well as at least one other element. Most of the Earth's crust consists of oxides. Oxides result when elements are oxidized by oxygen in air. Combustion of hydrocarbons affords the two principal oxides of carbon, carbon monoxide and carbon dioxide. Even materials that are of metals are generally basic In chemistry, a base is most commonly thought of as an aqueous substance that can accept hydrogen ions. A base is also often referred to as an alkali if OH− ions are involved. This refers to the Brønsted-Lowry theory of acids and bases. Alternate definitions of bases include electron pair donors , as sources of hydroxide anions (Arrhenius). In, as opposed to those of nonmetals, which are acidic An acid is traditionally considered any chemical compound that, when dissolved in water, gives a solution with a hydrogen ion activity greater than in pure water, i.e. a pH less than 7.0. That approximates the modern definition of Johannes Nicolaus Brønsted and Martin Lowry, who independently defined an acid as a compound which donates a hydrogen.

Painting Painting is the practice of applying paint, pigment, color or other medium to a surface . In art, the term describes both the act and the result, which is called a painting. Paintings may have for their support such surfaces as walls, paper, canvas, wood, glass, lacquer, clay or concrete. Paintings may be decorated with gold leaf, and some modern, anodising Anodizing, or anodising, is an electrolytic passivation process used to increase the thickness of the natural oxide layer on the surface of metal parts. Anodizing increases corrosion resistance and wear resistance, and provides better adhesion for paint primers and glues than bare metal. Anodic films can also be used for a number of cosmetic or plating Plating describes surface-covering where a metal is deposited on a conductive surface. Plating has been done for hundreds of years, but it is also critical for modern technology. Plating is used to decorate objects, for corrosion inhibition, to improve solderability, to harden, to improve wearability, to reduce friction, to improve paint adhesion, metals are good ways to prevent their corrosion Corrosion can be defined as the disintegration of a material into its constituent atoms due to chemical reactions with its surroundings. In the most common use of the word, this means a loss of electrons of metals reacting with water and oxygen. Weakening of iron due to oxidation of the iron atoms is a well-known example of electrochemical. However, a more reactive metal in the electrochemical series The table can be sorted alphabetically by clicking on the sort icon in the column heading. Click on the other column to re-sort by potential. This doesn’t work in the Safari web browser ; reload the page to restore the original order must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form an electrochemical cell An electrochemical cell is a device used for generating an electromotive force and current from chemical reactions, or the reverse, inducing a chemical reaction by a flow of current. The current is caused by the reactions releasing and accepting electrons at the different ends of a conductor. A common example of an electrochemical cell is a, and if the coating is less reactive than the coatee, the coating actually promotes corrosion.

Physical properties

Metals in general have high electric Electrical conductivity or specific conductance is a measure of a material's ability to conduct an electric current. When an electrical potential difference is placed across a conductor, its movable charges flow, giving rise to an electric current. The conductivity σ is defined as the ratio of the current density to the electric field strength :, thermal conductivity In physics, thermal conductivity, k, is the property of a material that indicates its ability to conduct heat. It appears primarily in Fourier's Law for heat conduction, luster Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. For example, a diamond is said to have an adamantine lustre and pyrite is said to have a metallic lustre. The term is also used to describe other items with a particular sheen (for example, fabric, especially silk and satin, or metals) and density The density of a material is defined as its mass per unit volume. The symbol of density is ρ, 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 The alkali metals are a series of chemical elements comprising Group 1 of the periodic table: lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs), and francium (Fr). (Hydrogen, although nominally also a member of Group 1, very rarely exhibits behavior comparable to the alkali metals). The alkali metals provide one of the best and alkaline earth The alkaline earth metals are a series of elements comprising Group 2 (Group IIA) of the periodic table: beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba) and radium (Ra). This specific group in the periodic table owes its name to their oxides that simply give basic alkaline solutions. These elements melt at such high metals) are extremely reactive, and are rarely encountered in their elemental, metallic form.^[1]

Density

The majority of metals have higher densities The density of a material is defined as its mass per unit volume. The symbol of density is ρ than the majority of nonmetals.^[1] Nonetheless, there is wide variation in the densities of metals; lithium Lithium is the chemical element with atomic number 3, and is represented by the symbol Li. It is a soft alkali metal with a silver-white color. Under standard conditions it is the lightest metal and the least dense solid element. Like all alkali metals lithium is highly reactive, corroding quickly in moist air to form a black tarnish. For this is the least dense solid element and osmium Osmium is a chemical element that has the symbol Os and atomic number 76. Osmium is a hard, brittle, blue-gray or blue-black transition metal in the platinum family, and is the densest natural element. The density of osmium is 22.61 g/cm3, slightly greater than that of iridium, the second densest element. Osmium is found in nature as an alloy, 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]

Malleability

The nondirectional nature of metallic bonding is thought to be the primary reason for the malleability of metal. Planes of atoms in a metal are able to slide across one another under stress, accounting for the ability of a crystal to deform without shattering.

When the planes of an ionic bond are slid 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 are not observed in covalently bonded crystals where fracture and thus crystal fragmentation occurs.

Conductivity

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.

Electric charge

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.

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. Examples of alloys are steel (iron and carbon), brass (copper and zinc), bronze (copper and tin), and duralumin (aluminium and copper). 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 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.^[2]

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.^[3]

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

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

Astronomy

In the specialised 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.^[4]

See also

• Amorphous metal
• ASM International (society)
• Electric field screening
• Metal theft
• Metalworking
• Periodic table (metals and non-metals)
• Properties and uses of metals
• Steel
• Structural steel
• Transition metal

References

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

External links

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