Transition Metals Learning Path

Definition and periodic-table classification

In chemistry, “transition metals” are defined primarily by their position on the periodic table: the elements in the d-block, corresponding to groups 3 to 12 (with some conventions allowing group 12 elements to be excluded). The IUPAC 2011 Principles of Chemical Nomenclature describe a transition metal as any element in groups 3–12, which matches the d-block definition used by many scientists. In practice, the f-block lanthanides and actinides are often treated separately as “inner transition metals,” though they are sometimes included under the broader idea of transition metals. The classification is also linked to electronic structure. Transition metals have atoms with partially filled d subshells (or can form cations with incomplete d subshells), and their d electrons (typically between 0 and 10 in the d-block) strongly influence their chemical behavior. As electrons are added across a transition series, they fill the same (n−1)d subshell, producing characteristic trends distinct from s- and p-block elements. Some periodic-table placements (notably involving group 3) can vary across published tables, and group 12 elements (Zn, Cd, Hg) are sometimes excluded because their d subshell is filled (d10) in their common oxidation states, though they may still show transition-metal-like bonding under certain criteria.

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d-Block versus inner transition metals

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