d and f-Block Elements - Complete Summary

Introduction to d-Block Elements

The d-block elements are known as transition elements because they represent a transition from the most electropositive s-block elements to the most electronegative p-block elements.

Transition Element: An element whose atom in ground state or ion in common oxidation state has incomplete d-subshell (d¹⁻⁹ electrons).

General Electronic Configuration

(n-1)d¹⁻¹⁰ ns¹⁻²

Exceptions

Zn, Cd, Hg have complete d¹⁰ configuration → not transition elements (group 12).

Group 3 (Sc, Y, La, Ac) and group 12 → non-typical transition elements.

Electronic Configurations

First Transition Series (3d)

Element	Symbol	At. No.	Configuration
Scandium	Sc	21	[Ar] 3d¹ 4s²
Titanium	Ti	22	[Ar] 3d² 4s²
Vanadium	V	23	[Ar] 3d³ 4s²
Chromium*	Cr	24	[Ar] 3d⁵ 4s¹
Manganese	Mn	25	[Ar] 3d⁵ 4s²
Iron	Fe	26	[Ar] 3d⁶ 4s²
Cobalt	Co	27	[Ar] 3d⁷ 4s²
Nickel	Ni	28	[Ar] 3d⁸ 4s²
Copper*	Cu	29	[Ar] 3d¹⁰ 4s¹
Zinc	Zn	30	[Ar] 3d¹⁰ 4s²

*Anomalous configurations due to stability of half-filled/full-filled orbitals.

Atomic and Ionic Radii

Trends in 3d Series (pm)

Element	K	Ca	Sc	Ti	V	Cr	Mn
Atomic Radius	227	197	144	132	122	117	117

Across Period

Decreases initially → minimum in middle → slight increase

Due to increasing nuclear charge & poor shielding by d-electrons

Down the Group

Increases due to addition of new shell

2nd & 3rd series similar due to lanthanide contraction

Ionisation Energies

Element	IE₁	IE₂	IE₃
Sc	632	1245	2450
Ti	659	1320	2721
Cr	652	1635	2994
Mn	716	1513	3258
Zn	906	1736	3838

Trend

Higher than s-block, lower than p-block

Gradual increase across series

5d > 4d > 3d series

Reason

Small atomic size

High nuclear charge

Poor shielding by d-electrons

Melting & Boiling Points

Very high (except Zn, Cd, Hg) due to strong metallic bonds with covalent character.

Trend

Increases to middle → decreases

Max at Cr (3d⁵ 4s¹) → 5 unpaired electrons

Strength of Bond

∝ number of unpaired d-electrons

Zn, Cd, Hg: d¹⁰ → no unpaired e⁻ → low MP

Oxidation States

Element	Config	Oxidation States
Sc	3d¹ 4s²	+2, +3
Ti	3d² 4s²	+2, +3, +4
V	3d³ 4s²	+2 to +5
Cr	3d⁵ 4s¹	+1 to +6
Mn	3d⁵ 4s²	+2 to +7
Fe	3d⁶ 4s²	+2, +3, +4, +5, +6
Ni	3d⁸ 4s²	+2, +3, +4
Cu	3d¹⁰ 4s¹	+1, +2
Zn	3d¹⁰ 4s²	+2

Key Points

Variable oxidation states due to ns and (n-1)d electrons
Most common: +2 (except Sc)
Highest: +7 (Mn), +8 (Ru, Os)
High OS in fluorides/oxides (covalent)
Low OS in carbonyls (e.g., Ni(CO)₄ → Ni⁰)

Coloured Ions

Due to d-d transition of electrons in presence of ligands.

Ion	Config	Unpaired e⁻	Colour
Sc³⁺	3d⁰	0	Colourless
Ti³⁺	3d¹	1	Purple
V³⁺	3d²	2	Green
Cr³⁺	3d³	3	Violet
Mn²⁺	3d⁵	5	Light pink
Fe³⁺	3d⁵	5	Yellow
Cu²⁺	3d⁹	1	Blue
Zn²⁺	3d¹⁰	0	Colourless

d-d Transition

Unpaired d-electrons absorb visible light → excited to higher d-orbital → complementary colour observed.

Magnetic Properties

Paramagnetic if unpaired electrons → attracted to magnetic field.

Trend

Increases to middle → decreases

Max at Mn²⁺, Fe³⁺ (5 unpaired e⁻)

Diamagnetic

Zn²⁺, Cu⁺, Sc³⁺ (d¹⁰ or d⁰)

Standard Electrode Potentials

Element	Ion	E° (V)
Sc	Sc³⁺	-2.10
Ti	Ti²⁺	-1.60
Mn	Mn²⁺	-1.18
Fe	Fe²⁺	-0.44
Cu	Cu²⁺	+0.34
Zn	Zn²⁺	-0.76

Negative E° → good reducing agents (except Cu).

Important Points for Exams

High Yield Concepts

Cr and Cu have anomalous configuration
Mn shows maximum oxidation states (+2 to +7)
Colour due to d-d transition, absent in d⁰ and d¹⁰
Magnetic moment ∝ √n(n+2) BM
Lanthanide contraction → similar radii of 4d and 5d
KMnO₄, K₂Cr₂O₇ → strong oxidants in +7, +6 states

JEE Main Weightage

Typically 2-3 questions from d-block. Focus on trends, oxidation states, colour, and magnetism.

Weightage High (2-3 Qs)