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Why d-block elements are called transition

Short answer

They are called transition elements because their properties are transitional between s-block (electropositive) and p-block (electronegative) elements. By IUPAC definition, a transition element must have an incompletely filled d subshell in the atom or a common ion. Not all d-block elements are transition; Zn, Cd and Hg have d¹⁰ in atom and M²⁺ ion, so they are d-block but not transition.

Why are transition elements called so? Are all d-block elements transition elements? Justify your answer with reason.

Why they are called transition elements

The d-block elements lie between the s-block (strongly electropositive, ionic compounds) and the p-block (electronegative, covalent compounds). Their properties are transitional between these two, so they are called transition elements. By the IUPAC definition, a transition element is one that has an incompletely filled d subshell, either in the atom or in any of its common ions.

Are all d-block elements transition elements?

No. Zn, Cd and Hg (group 12) have the configuration (n−1)d¹⁰ ns² in the atom and the d¹⁰ configuration in their only common ion (M²⁺ = d¹⁰). The d subshell is completely filled in both, so they do not show the typical transition properties (variable oxidation states, coloured ions, paramagnetism, strong catalytic activity). They are d-block elements but not transition elements. Cu (Cu²⁺ is d⁹) and Sc (Sc has 3d¹ in the atom) are considered transition elements because of the incomplete d subshell in the atom or in a common ion.

✓ Answer checked by Claude Opus 5.5 (high effort)

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