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are usually made of a metal cation and a nonmetal anion. Anions can be negatively charged ions made from , such as the oxide ion ($"O"^(2-)$), or chloride ion ($"Cl"^-"$). The anions can also by negatively charged , such as the nitrate ion ($"NO"_3^-$), or the sulfate ion ($"SO"_4^(2-)$).

Examples are:

Sodium oxide: $"Na"_2"O"$
Magnesium chloride: $"MgCl"_2$
Silver nitrate: $"AgNO"_3$
Aluminum sulfate: $"Al"_2"(SO"_4)_3$