What are the chemical properties of metals?
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Metals are usually inclined to form cationsthrough electron loss,[6] reacting with oxygen in the air to form oxides over various timescales (iron rusts over years, whilepotassium burns in seconds). Examples:
4 Na + O2 → 2 Na2O (sodium oxide)2 Ca + O2 → 2 CaO (calcium oxide)4 Al + 3 O2 → 2 Al2O3 (aluminium oxide).
The transition metals (such as iron, copper,zinc, and nickel) are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium,platinum and gold, do not react with the atmosphere at all. 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 (likealuminium, magnesium, some steels, andtitanium). The oxides of metals are generallybasic, as opposed to those of nonmetals, which are acidic. Exceptions are largely oxides with very high oxidation states such as CrO3, Mn2O7, and OsO4, which have strictly acidic reactions.
Painting, anodizing or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form anelectrochemical cell, and if the coating is less reactive than the coatee, the coating actuallypromotes corrosion.
4 Na + O2 → 2 Na2O (sodium oxide)2 Ca + O2 → 2 CaO (calcium oxide)4 Al + 3 O2 → 2 Al2O3 (aluminium oxide).
The transition metals (such as iron, copper,zinc, and nickel) are slower to oxidize because they form a passivating layer of oxide that protects the interior. Others, like palladium,platinum and gold, do not react with the atmosphere at all. 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 (likealuminium, magnesium, some steels, andtitanium). The oxides of metals are generallybasic, as opposed to those of nonmetals, which are acidic. Exceptions are largely oxides with very high oxidation states such as CrO3, Mn2O7, and OsO4, which have strictly acidic reactions.
Painting, anodizing or plating metals are good ways to prevent their corrosion. However, a more reactive metal in the electrochemical series must be chosen for coating, especially when chipping of the coating is expected. Water and the two metals form anelectrochemical cell, and if the coating is less reactive than the coatee, the coating actuallypromotes corrosion.
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