|transition element or transition metal|
|chem any element belonging to one of three series of elements with atomic numbers between 21 and 30, 39 and 48, and 57 and 80. They have an incomplete penultimate electron shell and tend to exhibit more than one valency and to form complexes|
|transition metal or transition metal|
|transition element (trān-zĭsh'ən) Pronunciation Key
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.