transition element

WordReference Random House Unabridged Dictionary of American English © 2026

transi′tion el′ement, [Chem.]

1. any element in any of the series of elements with atomic numbers 21–29, 39–47, 57–79, and 89–107, that in a given inner orbital has less than a full quota of electrons. Also called transi′tion met′al.

• 1920–25

Collins Concise English Dictionary © HarperCollins Publishers::

transition element, transition metal noun

1. 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