Monatomic anions are named by adding the suffix –ide and the word ion to the first part of the name of the element ( the “stem” of its name ). There is no need to give the charge, because most elements that form monatomic anions form only one kind of ion.The ions formed by the halogens are collectively called halide ions and include
fluoride (F-), chloride (Cl-), bromide (Br-), and iodide ions (I-).
The names of oxoanions are formed by adding the suffix –ate to the stem of the name of the element that is not oxygen, as in the carbonate ion, CO32-. However, many elements can form a variety of oxoanions with different numbers of oxygen atoms; nitrogen, for example, forms both NO2- and NO3-. In such cases, the ion with the larger number of oxygen atoms is given the suffix –ate, and that with the smaller number of oxygen atoms is given the suffix –ite. Thus, NO2- is nitrate and NO3- is nitrite.
Some elements-particularly take for the halogens—form more than two oxoanions. The name of the oxoanion with the smallest number of oxygen atoms is formed by adding the prefix hypo- to the –ite form of the name, as in the hypochlorite ion, ClO-. The oxoanion with a higher number of oxygen atoms than the –ate oxoanion is named with the prefix per- added to the –ate form of the name.
An example is the perchlorate ion, ClO4-.
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Some anions include hydrogen, such as HS- and HCO3-. The names of these anions begin with “hydrogen”. Thus, HCO3- is the hydrogen carbonate ion.In an older system of nomenclature, an anion containing a hydrogen atom was named with the prefix bi-, as in bicarbonate ion for HCO3-.
The oxoacids are molecular compounds that can be regarded as the parents of the oxoanions. The formulas of oxoacids are derived from those of the corresponding oxoanions by adding enough hydrogen ions to balance the charges. This procedure is only a formal way of building the chemical formula, because oxoacids are all molecular compounds.
For example, the sulfate ion, SO42-, needs two H+ ions to cancel its negative charge, so sulfuric acid is the molecular compound H2SO4.Similarly, the phosphate ion, PO43-, needs these H+ ions, so its parent acid is the molecular compound H3PO4, phosphoric acid.As these examples illustrate, the names of the parent oxoacids are derived from those of the corresponding oxoanions by replacing the –ate suffix with –ic acid. In general, -ic oxoacids are the parents of –ate oxoanions and –ous oxoacids are the parents of –ite oxoanions.