Transition Element
An element whose atom or a stable ion has a partially filled d subshell.
Formula / equation
(n−1)d¹⁻⁹
Unit
Dimensionless
In depth
The strict IUPAC definition excludes zinc, cadmium and mercury, whose d shells are always full. Partly filled d orbitals allow d–d electronic transitions that absorb visible light, unpaired electrons that produce paramagnetism, and easily interconverted oxidation states that underpin catalysis.
Examples in the real world
Manganese ranging from +2 to +7; the deep purple of MnO₄⁻ and the blue of [Cu(H₂O)₆]²⁺.