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IUPAC 2011 defines transition metals as elements in periodic-table groups 3–12, aligning with the d-block; f-block lanthanides/actinides are often treated separately as inner transition metals.
In chemistry, a transition metal is defined primarily by its position on the periodic table: it is an element in the d-block, corresponding to groups 3 to 12 (with some variations in practice). The IUPAC 2011 Principles of Chemical Nomenclature describe a transition metal as any element in groups 3–12, which matches the d-block elements. In practice, the lanthanides and actinides (f-block) are often treated separately as “inner transition metals,” though some sources may still consider them transition metals. Classification can vary for certain borderline cases. Group 12 elements (Zn, Cd, Hg) are sometimes excluded because their d subshell is filled (d10), meaning they do not show the same typical behavior associated with partially filled d subshells; however, they are often included for convenience in discussions of transition-element chemistry. The placement of group 3 elements (Sc/Y vs La/Ac vs Lu/Lr) also shows variation across periodic-table formats, with updated IUPAC-supported arrangements favoring Lu and Lr in group 3 to preserve atomic-number order and the correct f-block width. Transition metals are further described as “early” or “late” depending on which d-block groups they occupy, and some heavier group 2 elements (e.g., Ca, Sr, Ba) are sometimes called “honorary” transition metals due to d-orbital participation in bonding.
IUPAC 2011 defines transition metals as elements in periodic-table groups 3–12, aligning with the d-block; f-block lanthanides/actinides are often treated separately as inner transition metals.
Group 12 elements (Zn, Cd, Hg) are sometimes excluded due to a filled d10 subshell, but may be included depending on the context and bonding/complexation considerations.
Periodic-table classification can vary for group 3 placement (Sc/Y vs La/Ac vs Lu/Lr) and for early vs late transition metals, reflecting different conventions and the need to preserve periodic-table structure constraints.
A chemical element in the d-block, commonly defined as any element in groups 3–12 of the periodic table (with some conventions that may exclude group 12 or treat f-block elements separately).
The set of elements whose atoms have electrons filling the d subshell, corresponding to groups 3–12 on the periodic table.
A lanthanide or actinide (f-block element) often treated separately from the d-block transition metals.
The elements Zn, Cd, and Hg, which are sometimes excluded from transition metals because their d subshell is filled (d10) in common oxidation states.
A classification scheme where early transition metals occupy the left side of the d-block (lower groups) and late transition metals occupy the right side (higher groups).
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