Any of the metallic elements within Groups 3 through 12 in the Periodic Table. All the transition metals have two electrons in their outermost shell, and all but zinc, cadmium, and mercury have an incompletely filled inner shell (just inside the outermost shell). Transition elements form alloys easily, have high melting points, and have more than one valence because of their incomplete inner shells. See Periodic Table. See Note at metal.