metal: Chemical Properties
Chemically, the metals differ from the nonmetals in that they form positive ions and basic oxides and hydroxides. Upon exposure to moist air, a great many undergo corrosion, i.e., enter into a chemical reaction; e.g., iron rusts when exposed to moist air, the oxygen of the atmosphere uniting with the metal to form the oxide of the metal. Aluminum and zinc do not appear to be affected, but in fact a thin coating of the oxide is formed almost at once, stopping further action and appearing unnoticeable because of its close resemblance to the metal. Tin, lead, and copper react slowly under ordinary conditions. Silver is affected by compounds such as sulfur dioxide and becomes tarnished when exposed to air containing them. The metals are combined with nonmetals in their salts, as in carbides, carbonates, chlorides, nitrates, phosphates, silicates, sulfides, and sulfates.
On the basis of their ability to be oxidized, i.e., lose electrons, metals can be arranged in a list called the electromotive series, or replacement series. Metals toward the beginning of the series, like cesium and lithium, are more readily oxidized than those toward the end, like silver and gold. In general, a metal will replace any other metal, or hydrogen, in a compound that it precedes in the series, and under ordinary circumstances it will be replaced by any metal, or hydrogen, that it follows.
Metals fall into groups in the periodic table determined by similar arrangements of their orbital electrons and a consequent similarity in chemical properties. Groups of similar metals include the alkali metals (Group 1 in the periodic table), the alkaline-earth metals (Group 2 in the periodic table), and the rare-earth metals (the lanthanide and actinide series of Group 3). Most metals other than the alkali metals and the alkaline earth metals are called transition metals (see transition elements). The oxidation states, or valence, of the metal ions vary from +1 for the alkali metals to as much as +7 for some transition metals.
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