d- and f-Block Elements

Syllabus Unit: Inorganic Chemistry

Why it matters

Chapter overview

The d-block (groups 3–12) and f-block (lanthanoids, actinoids) owe their entire chemical personality to partially filled d- and f-subshells: variable oxidation states, coloured ions, magnetic behaviour, and catalytic activity all trace back to this one structural fact. NEET tests the Cr/Cu configuration exceptions, the d-d transition origin of colour, Mn's unusually wide oxidation-state range, and lanthanoid contraction's knock-on effect of making 4d and 5d congeners nearly identical in size.

Chemistry Syllabus Inorganic Chemistry ~25% weightage

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Sc–V: fill 3d regularly (3d1 4s2 → 3d3 4s2)

Cr: jumps to 3d5 4s1 (half-filled stability)

Mn–Ni: resume regular filling (3d5 4s2 → 3d8 4s2)

Cu: jumps to 3d10 4s1 (fully-filled stability)

1Transition Elements & Configurations

Transition elements are defined by a partially filled d-subshell in the atom or a common ion — the single structural fact behind every hallmark property of this block.

Learning Objectives

Define a transition element per IUPAC (partially filled d-subshell in the atom or a common ion) and identify why Zn, Cd, Hg are excluded.
Write the general electronic configuration (n−1)d1–10 ns1–2 and explain the Cr and Cu exceptions.
Explain why transition metals have unusually high melting and boiling points.
Describe how atomic radii change across a transition series compared to a main-group period.

Key Terms

Transition ElementAn element whose atom, or a common ion it forms, has a partially (incompletely) filled d-subshell (IUPAC definition).

Aufbau ExceptionCr ([Ar]3d5 4s1) and Cu ([Ar]3d10 4s1) adopt a single 4s electron instead of the expected two, because a half-filled or fully-filled d-subshell is extra stable.

d-BlockGroups 3–12 of the periodic table, where electrons progressively fill the (n−1)d orbitals.

Metallic Bonding (d-block)Both ns and (n−1)d electrons participate in the electron sea/delocalised bonding, giving transition metals unusually strong metallic bonds and high melting points.

A transition element, by IUPAC definition, has a partially filled d-subshell in its atomic ground state or in at least one commonly formed ion. This single criterion explains why Zn, Cd and Hg (always d10) are placed in the d-block but excluded from 'transition element' behaviour.

General configuration and its exceptions

The general configuration across a d-block series is (n−1)d1–10 ns1–2. Two period-4 exceptions are classic NEET questions: chromium is [Ar]3d5 4s1 (not 3d4 4s2) because a half-filled d-subshell is extra stable, and copper is [Ar]3d10 4s1 (not 3d9 4s2) because a fully-filled d-subshell is extra stable.

Why transition metals have high melting/boiling points

Both the (n−1)d and ns electrons participate in metallic bonding, giving a stronger 'electron sea' than typical main-group metals.
Greater the number of unpaired d-electrons available for bonding, generally the higher the melting point — tungsten (5d4 6s2) has one of the highest melting points of any element.

Key PointAtomic radii fall sharply from group 3 to about group 6, then stay nearly constant to group 10 before rising slightly at Cu/Zn — the added d-electrons shield the outer 4s electrons from the rising nuclear charge, roughly cancelling it out mid-series.

General configuration: (n−1)d1–10 ns1–2 | Exceptions: Cr = 3d5 4s1, Cu = 3d10 4s1