A metal is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. In metallurgy, a metal is an element that readily forms cations and has metallic bonds. Metallic elements are sometimes grouped together based on their physical properties into metalloids and metals. A metal may be a chemical element such as iron; an alloy such as stainless steel; or a compound such as mercury.
The three primary classifications of metals are the transition metals, main group (or native) metals, and rare earth metals. The first two groups show similar properties – they form alloys with other metals (and in some cases nonmetals), conduct heat and electricity easily, and have high melting points and densities. The rare earths generally have very different properties from the other two groups: They tend to be much harder than either transition or main group metals; they are poor conductors of heat but good electrical insulators; many have very low melting points; they usually exist in nature only in compounds rather than in pure form; their density varies widely. Each of these classifications can be further subdivided into subclasses based on additional shared physical or chemical characteristics.
The term “metal” is derived from the Latin word “metallum” which means “mine” or “quarry”. The Latin word probably originated from the Etruscan word “metal”, which was found on objects dating back to 2500 BC. Metals were known in antiquity, but their discovery came late compared to that of other materials because they required smelting at high temperatures for extraction. Some early examples of smelted metal objects include copper beads dating back to 8700 BC found in Anatolia (modern Turkey) and bronze tools dating back to 3400 BC found in modern-day Romania.
The first systematic classification of the metallic elements was published by Johann Wolfgang Döbereinerin 1829, who grouped them by similarities in their analytical chemistry results. This led to inconsistencies between his systemand Mendeleev’s periodic table when it was published just nine years later, so Doberer’s nomenclatureis not used today. However, his work did contribute to our current understandingof how certain elements behave chemically because he observed trends withinhis groups that were later explained using quantum mechanics. For example: alkali metals always lose one electron when forming cations while chalcogens always gain two electrons when forming anions.