| In chemistry, a metal (Greek: Metallon)
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| | metals form an electrochemical cell, and
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| is an element that readily forms positive
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| | if the coating is less reactive than the
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| ions (cations) and has metallic bonds.
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| | coatee, the coating actually promotes
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| Metals are sometimes described as a
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| | corrosion.
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| lattice of positive ions surrounded by a
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| | Physical properties
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| cloud of delocalized electrons. The
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| | Traditionally, metals have certain
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| metals are one of the three groups of
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| | characteristic physical properties: they
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| elements as distinguished by their
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| | are usually shiny (they have "luster"),
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| ionization and bonding properties, along
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| | have a high density, are ductile and
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| with the metalloids and nonmetals. On the
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| | malleable, usually have a high melting
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| periodic table, a diagonal line drawn
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| | point, are usually hard, and conduct
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| from boron (B) to polonium (Po) separates
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| | electricity and heat well. However this
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| the metals from the nonmetals. Most
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| | is mainly because the low density, soft,
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| elements on this line are metalloids,
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| | low melting point metals happen to be
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| sometimes called semi-metals; elements to
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| | reactive, and we rarely encounter them in
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| the lower left are metals; elements to
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| | their elemental, metallic form. Metals
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| the upper right are nonmetals.
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| | conduct sound well, that is, they are
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| A modern definition of metals is that
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| | sonorous.
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| they have overlapping conduction bands
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| | The electrical and thermal conductivity
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| and valence bands in their electronic
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| | of metals originate from the fact that in
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| structure. This definition opens up the
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| | the metallic bond the outer electrons of
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| category for metallic polymers and other
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| | the metal atoms form a gas of nearly free
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| organic metals, which have been made by
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| | electrons, moving as an electron gas in a
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| researchers and employed in high-tech
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| | background of positive charge formed by
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| devices. These synthetic materials often
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| | the ion cores. Good mathematical
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| have the characteristic silvery-grey
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| | predictions for electrical conductivity,
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| reflectiveness (luster) of elemental
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| | as well as the electrons' contribution to
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| metals.
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| | the heat capacity and heat conductivity
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| The traditional definition focuses on the
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| | of metals can be calculated from the free
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| bulk properties of metals. They tend to
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| | electron model, which does not take the
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| be lustrous, ductile, malleable, and good
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| | detailed structure of the ion lattice
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| conductors of electricity, while
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| | into account.
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| nonmetals are generally brittle (if
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| | When considering the exact band structure
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| solid), lack luster, and are insulators.
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| | and binding energy of a metal, it is
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| Chemical properties
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| | necessary to take into account the
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| Most metals are chemically reactive,
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| | positive potential caused by the specific
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| reacting with oxygen in the air to form
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| | arrangement of the ion cores - which is
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| oxides over varying timescales (for
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| | periodic in crystals. The most important
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| example iron rusts over years and
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| | consequence of the periodic potential is
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| potassium burns in seconds). The alkali
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| | the formation of a small band gap at the
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| metals react quickest followed by the
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| | boundary of the brillouin zone.
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| alkaline earth metals, found in the
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| | Mathematically, the potential of the ion
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| leftmost two groups of the periodic
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| | cores is treated in the nearly-free
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| table. The transition metals take much
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| | electron model.
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| longer to oxidize (such as iron, copper,
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| | Alloys
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| zinc, nickel). Others, like palladium,
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| | An alloy is a mixture of two or more
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| platinum and gold, do not react with the
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| | elements in solid solution in which the
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| atmosphere at all. Some metals form a
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| | major component is a metal. Most pure
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| barrier layer of oxide on their surface
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| | metals are either too soft, brittle or
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| which cannot be penetrated by further
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| | chemically reactive for practical use.
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| oxygen molecules and thus retain their
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| | Combining different ratios of metals as
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| shiny appearance and good conductivity
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| | alloys modify the properties of pure
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| for many decades (like aluminium, some
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| | metals to produce desirable
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| steels, and titanium). The oxides of
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| | characteristics. The aim of making alloys
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| metals are basic (as opposed to those of
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| | is generally to make them less brittle,
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| nonmetals, which are acidic), although
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| | harder, resistant to corrosion, or have a
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| this may be considered a rule of thumb,
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| | more desirable color and luster. Examples
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| rather than a fact.
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| | of alloys are steel (iron and carbon),
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| Painting or anodising metals are good
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| | brass (copper and zinc), bronze (copper
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| ways to prevent their corrosion. However,
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| | and tin), and duralumin (aluminium and
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| a more reactive metal in the
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| | copper). Alloys specially designed for
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| electrochemical series must be chosen for
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| | highly demanding applications, such as
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| coating, especially when chipping of the
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| | jet engines, may contain more than ten
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| coating is expected. Water and the two
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| | elements.
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