Elements in the d-block (Groups 3–12) of the periodic table are referred to as transition metals. (The lanthanides and actinides are usually excluded.) With the exception of Group 12, the transition metal elements have an incomplete d-shell of electrons. The chemistry of these elements depends strongly on these d-electrons, and most transition metals are stable in multiple different oxidation states. If the metal has any unpaired d-electrons, it can have magnetic properties. Many transition metals have uses as catalysts in bond-forming reactions, and we’ll talk about a few later in this chapter.