To create a query that includes an atom that can be one of multiple elements, you start by drawing the substructure with an atom of a single element (for example a carbon), that is a standard substructure search. Once the atom is placed that you would like to allow be one of multiple elements, you can change the atom's allowed elements by right-clicking the atom in question, selecting Query Features, selecting List, and then selecting Set... . This will show the periodic table. In here, you can select the elements you want to allow and then click done. The atom will then be labeled with the allowed elements, though it may be truncated if you have selected more than a few. You can change the list of allowed elements by selecting the atom, right-clicking and selecting Query Features, then List, then the element list. The periodic table will reappear with the atoms selected. These can be modified as needed. The list can be cleared by right-clicking the atom and selecting Query Features, then List, and then Clear.