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 M_xH_y 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.