http://www.ck12.org Chapter 7. Chemical Nomenclature
TABLE7.3:(continued)
1- 2- 3- 1+
chlorite, ClO 2 − hydrogen phosphate,
HPO 42 −
cyanide, CN− peroxide, O 22 −
dihydrogen phosphate,
H 2 PO 4 −sulfate, SO 42 −hydrogen carbonate,
HCO 3 −sulfite, SO 32 −hydrogen sulfate, HSO 4 −
hydrogen sulfide, HS−
hydroxide, OH−
hypochlorite, ClO−
nitrate, NO 3 −
nitrite, NO 2 −
perchlorate, ClO 4 −
permanganate, MnO 4 −Oxoanions
Note that the vast majority of polyatomic ions are anions, many of which end in–ateor–ite. In some cases,
such as nitrate (NO 3 −) and nitrite (NO 2 −), there are multiple anions that consist of the same two elements. This is
particularly common foroxoanions, which are anions in which one or more oxygen atoms are all bonded to a central
atom of some other element. A given element may form several oxoanions that all have the same charge but differ
in the number of oxygen atoms present. When there are two common oxoanions for a particular element, the one
with the greater number of oxygen atoms gets an–atesuffix, while the one with the lower number of oxygen atoms
gets an–itesuffix. Some elements form more than two common oxoanions, such as chlorine:
- ClO−, hypochlorite
- ClO 2 −, chlorite
- ClO 3 −, chlorate
- ClO 4 −, perchlorate
For larger families of oxoanions, the ion with one more oxygen atom than the–ateanion is given aper-prefix,
and the ion with one fewer oxygen atom than the–iteanion is given ahypo-prefix. Organizing oxoanions in the
following format (inTable7.9) may help with memorization:
TABLE7.4: Common Oxoanions
Central Atom Root 1 more oxygen “normal” 1 less oxygen 2 less oxygens
Chlorine chlor- ClO 4 −perchlorateClO 3 −chlorate ClO 2 −chlorite ClO−hypochlorite
Bromine brom- BrO 4 − BrO 3 − BrO 2 − BrO−
Iodine iod- IO 4 − IO 3 −
Sulfur sulf- SO 52 − SO 42 − SO 32 − SO 22 −
Nitrogen nitr- NO 3 − NO 2 −
Phosphorus phosph- PO 43 − PO 33 − PO 23 −
Carbon carbon- CO 32 −