D-block

D-block is the section of the periodic table comprising elements whose outermost electrons occupy the d orbital. The d orbital can hold up to ten electrons, so the d-block contains ten groups in the middle of the periodic table, spanning from group 3 to group 12.

D-block elements are commonly called transition metals. All are metals: they have high thermal and electrical conductivity, high melting points and hardness, and can have multiple oxidation states. Common examples include iron (Fe), copper (Cu), titanium (Ti), chromium (Cr), nickel (Ni), and gold (Au).

Electron Configuration

The general electron configuration pattern of d-block elements is (n−1)d followed by ns, meaning the d orbital of a lower shell fills after the s orbital of a higher shell begins to fill. This results in the energies of the d and s orbitals being very close, allowing electrons to participate in chemical bonding between them. There are notable exceptions—such as chromium and copper—where the actual configuration differs from the simple pattern due to the extra stability of half-filled or filled d orbitals.

Chemical Properties

Because of their multiple oxidation states, d-block elements form many colored compounds and are known for producing coordination complexes with ligands surrounding metal ions. This property underpins coordination chemistry. Additionally, many d-block elements serve as industrial catalysts, for example iron in the Haber process and platinum in vehicle emission control systems.

Boundaries and Divisions

D-block consists of four periods: period 4 (Sc to Zn), period 5 (Y to Cd), period 6 (Hf to Hg), and period 7 (Rf onward), some of whose elements are synthetic and highly unstable. Group 12—zinc, cadmium, mercury—are sometimes excluded from the definition of transition metals because their d orbitals are completely filled and do not participate in ordinary bonding.