Complex ion

An ion consisting of multiple atoms associated together by covalent bonds which can be considered as acting as a single unit in the context of acid/base chemistry or in the formation of salts.

Some commonly-occuring complex ions and their charges are indicated below

 carbonate    CO32-

 bicarbonate  HCO3-

 nitrate      NO3-

 phosphate    PO43-

 sulfate?      SO42-

 acetate?      CH3C(=O)O-

 ammonium?     NH4+

 hydroxide    OH-

 pyridinium?   C5H5NH+