![]() 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. Metals conduct sound well, that is, they are sonorous. However this is mainly because the low density, soft, low melting point metals happen to be reactive, and we rarely encounter them in their elemental, metallic form. Traditionally, metals have certain characteristic physical properties: they are usually shiny (they have "lustre"), have a high density, are ductile and malleable, usually have a high melting point, are usually hard, and conduct electricity and heat well. ![]() Water and the two metals form an electrochemical cell, and if the coating is less reactive than the coatee, the coating actually promotes corrosion. ![]() However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Painting or anodising metals are good ways to prevent their corrosion. The oxides of metals are basic (as opposed to those of nonmetals, which are acidic), although this may be considered a rule of thumb, rather than an absolute condition. 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). Others, like palladium, platinum and gold, do not react with the atmosphere at all. The transition metals take much longer to oxidise (such as iron, copper, zinc, nickel). The alkali metals react quickest followed by the alkaline earth metals, found in the leftmost two groups of the periodic table. Most metals are chemically unstable, reacting with oxygen in the air to form oxides over varying timescales (for example iron rusts over years and potassium burns in seconds). Some popular metals are aluminium, copper, gold, iron, lead, silver, titanium, uranium and zinc. Nonmetal elements are more commonplace on Earth than metallic elements are, but metals in fact constitute most of the periodic table. They tend to be lustrous, ductile, malleable, and good conductors of electricity, while nonmetals are generally brittle (for solid nonmetals), lack lustre, and are insulators. The traditional definition focuses on the bulk properties of metals. These synthetic materials often have the characteristic silvery-grey reflectiveness of elemental metals. 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. Elements on this line are metalloids, sometimes called semi-metals elements to the lower left are metals elements to the upper right are nonmetals.Ī modern definition of metals is that they have overlapping conduction bands and valence bands in their electronic structure. On the periodic table, a diagonal line drawn from boron (B) to polonium (Po) separates the metals from the nonmetals. The metals are one of the three groups of elements as distinguished by their ionisation and bonding properties, along with the metalloids and nonmetals. Metals are sometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons. In chemistry, a metal ( Greek: Metallon) is an element that readily forms positive ions (cations) and has metallic bonds.
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