d-Block Transition Elements
Definition and meaning of d-Block Transition Elements in chemistry.
D-transition elements (transition metals) are the metallic elements of groups 3–12, located in the d-block of the periodic table, whose atoms, or at least one of their common ions, have a partially filled d subshell.
In more detail
Because their (n-1)d orbitals are only partly occupied, these elements readily lose different numbers of electrons, giving rise to multiple oxidation states within the same element. Partially filled d orbitals also allow d-to-d electron transitions, which is why many transition metal ions and compounds are colored, and unpaired d electrons make many of them paramagnetic. Their ions and atoms form coordination complexes with ligands, and the metals themselves (and their compounds) are widely used as catalysts, such as iron in the Haber process and platinum in catalytic converters. By strict IUPAC definition, group 12 elements (Zn, Cd, Hg) are d-block but not true transition metals, since both the atom and its common ions have a fully filled d10 configuration.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Location | Groups 3-12 (d-block), periodic table |
| Key feature | Partially filled (n-1)d subshell in atom or common ion |
| Typical examples | Fe, Cu, Ni, Cr, Mn, Ti |
Iron ([Ar]3d6 4s2) is a d-transition element: it forms Fe2+ (3d6) and Fe3+ (3d5) ions, gives colored compounds such as yellow-brown FeCl3 and red-brown Fe2O3, and acts as a catalyst in the Haber-Bosch process for ammonia synthesis.
Frequently asked questions
Are zinc, cadmium, and mercury transition metals?
They are d-block elements but not transition metals by the strict IUPAC definition, because their atoms and common ions (Zn2+, Cd2+, Hg2+) all have a completely filled 3d10 (or equivalent) subshell, so there is no partially filled d subshell.
Why are many transition metal compounds colored?
Ligands or other groups around the metal ion split its d orbitals into slightly different energy levels; visible light can promote electrons between these levels (d-d transitions), and the wavelengths absorbed give the complementary color we observe.