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Metal
In chemistry, a metal is an element that readily loses electrons to form positive ions (cations) and has metalic bonds between metal atoms. Metals form ionic bonds with non-metals. They are sometimes described as a lattice of positive ions surrounded by a cloud of delocalized electrons. The metals are one of the three groups of elements as distinguished by their ionization and bonding properties, along with the metalloids and nonmetals. On the periodic table, 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 semi-metals; elements to the lower left are metals; elements to the upper right are nonmetals.
Alloy
An alloy is a homogeneous hybrid of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. The resulting metallic substance usually has different properties (sometimes substantially different) from those of its components. Alloys are usually prepared to improve on the properties of other elements. For instance,steel is stronger than iron, its primary element. The physical properties of an alloy, such as density, reactivity, Young's modulus, and electrical and thermal conductivity may not differ greatly from the alloy's elements, but engineering properties, such as tensile strength and shear strength can be substantially different from those of the constituent materials. This is sometimes due to the differing sizes of the atoms in the alloy, since larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors. This helps the alloy resist deformation, unlike a pure metal where the atoms move more freely. Alloys may exhibit marked difference in behaviour even in the case of small amounts of impurities being one element of the alloy; for example impurities in semiconducting ferromagnetic alloys lead to different properties as first predicted by White, Hogan, Suhl and Nakamura.