Parent cation | Name | Parent cation | Name |
---|---|---|---|
NH4+ | ammonium | SeH3+ | selenonium |
PH4+ | phosphonium | TeH3+ | telluronium |
AsH4+ | arsonium | FH2+ | fluoronium |
SbH4+ | stibonium | ClH2+ | chloronium |
BiH4+ | bismuthonium | BrH2+ | bromonium |
OH3+ | oxonium | IH2+ | iodonium |
SH3+ | sulfonium |
Please observe that each of these -onium ions has a positive charge. The reason they have an overall positive charge is that they each contain one bond (e.g., an addition bond to hydrogen when it accepts the H+ ion) more than is necessary to form a neutral compound (e.g., H20 accepts a H+ to become H3O+; HF accepts a H+ to become H2F+, etc.). You should also remember that the suffix -onium usually always refers to a positively charged ion.
To name an onium ion, use the parent (root) name of the element in the compound and add -onium to the name. A certain amount of phonetic juggling occurs, but the root name is still recognizable.
Finally, if the "oxygen" that accepts the additional H+ ion is part of an alcohol, then the resulting onium ion would be an "alkyloxonium" ion, since there is a carbon group (alkyl group) that would also now be attached to that oxygen.
Copyright © Dr. Donald L. Robertson (Modified: 11/16/2010)