d- and f-Block Elements

Syllabus Unit: Inorganic Chemistry

Why it matters

Chapter overview

The d-block (transition metals) and f-block (lanthanoids, actinoids) owe nearly all of their signature chemistry to one structural fact: a partly-filled d- or f-subshell. This single idea explains variable oxidation states, coloured and paramagnetic ions, catalytic activity, and the famous lanthanide contraction that JEE tests across this entire unit.

Chemistry Syllabus Structure Inorganic Chemistry ~33% weightage

Live Animation1 / 4

3d Transition Series

1Sc-Ti-VEarly series, d1-d3

2CrAnomalous d5 4s1

3Fe-Co-Nid6-d8, ferromagnetic

4Cu-Znd10 boundary

1Transition Metals & Their Configurations

Transition elements are defined by an incomplete d-subshell in some common state, with chromium and copper famously borrowing a 4s electron to reach extra-stable half-filled or fully-filled 3d configurations.

Learning Objectives

State the general electronic configuration (n-1)d1-10 ns0-2 and the IUPAC definition of a transition element.
Explain why Cr ([Ar]3d5 4s1) and Cu ([Ar]3d10 4s1) deviate from the Aufbau-predicted configuration.
Explain why Zn, Cd and Hg are not classified as true transition elements despite being in the d-block.
List the general physical properties (high melting point, alloy formation, metallic bonding) shared by transition metals.

Key Terms

Transition elementAn element whose atom, or one of whose common ions, has an incomplete d-subshell (IUPAC definition).

Aufbau exceptions (Cr, Cu)Cr and Cu adopt a 4s1 (not 4s2) configuration because a half-filled (d5) or fully-filled (d10) d-subshell provides extra exchange stabilisation.

(n-1)d ns configurationThe general valence pattern of d-block elements, where the (n-1)d subshell fills after the ns subshell is already occupied.

Zn/Cd/Hg exclusionThese elements have a complete d10 configuration in both the atom and the +2 ion, so they possess no incomplete d-subshell and are excluded from the strict definition of a transition element.

d-block elements have the general configuration (n-1)d1-10 ns0-2. IUPAC defines a **transition element** specifically as one whose atom, or one of whose commonly formed ions, has an incomplete d-subshell.

The Cr and Cu exceptions

Chromium: predicted [Ar]3d4 4s2, actual [Ar]3d5 4s1 — a half-filled 3d5 combined with a half-filled 4s1 gains extra exchange stabilisation.
Copper: predicted [Ar]3d9 4s2, actual [Ar]3d10 4s1 — a fully-filled 3d10 subshell is more stable than a partly-filled one.

Why Zn, Cd and Hg don't count as transition metals

Zinc, cadmium and mercury have a complete d10 configuration in both the neutral atom and their common +2 ion — since neither state has an incomplete d-subshell, they fail the IUPAC definition despite sitting in the d-block by position.

General properties

High melting and boiling points from strong metallic bonding involving d-electrons.
Readily form alloys (similar atomic sizes allow substitution in the metal lattice).
Good electrical and thermal conductors.
Show variable oxidation states, and are often coloured and paramagnetic (see next subtopic).

Exam TipJEE frequently asks which d-block element is NOT a transition element — the answer is Zn, Cd or Hg, since all common oxidation states leave the d-subshell completely full.