WebElements: Actinium compounds
This section lists some binary compounds with halogens (known as halides), oxygen (known as oxides), hydrogen (known as hydrides), and some other compounds of actinium. For each compound, a formal oxidation number for actinium is given, but the usefulness of this number is limited for p-block elements in particular. Based upon that oxidation number, an electronic configuration is also given but note that for more exotic compounds you should view this as a guide only. The term hydride is used in a generic sense to indicate compounds of the type MxHy and not necessarily to indicate that any compounds listed behave chemically as hydrides. In compounds of actinium (where known), the most common oxidation numbers of actinium are: 3.