The d- and f-Block Elements

The d-block elements occupy the large middle section of the periodic table, spanning Groups 3 to 12. They are known as "Transition Elements" as they represent a transition in properties from s-block metals to p-block non-metals.

The f-block (Groups 3, Period 6 & 7) elements are placed separately at the bottom to maintain the periodic table's structure. These are the Inner Transition Elements.

Transition metals are characterized by the filling of (n-1)d orbitals. Their chemistry is dominated by their ability to use both 'ns' and '(n-1)d' electrons for bonding, leading to variable oxidation states and complex formation.

General Configuration:

The stability of configurations is governed by Exchange Energy and Symmetry.

A. Enthalpy of Atomization

Transition metals exhibit high enthalpies of atomization due to strong interatomic metallic bonding involving a large number of unpaired electrons.

B. Electrode Potentials (E°)

The trend in $E^\circ(M^{2+}/M)$ is irregular. It depends on the balance between Enthalpy of Sublimation, Ionization Enthalpy, and Hydration Enthalpy.

• Copper: Positive $E^\circ$ value (+0.34V) means it cannot liberate Hydrogen from acids. This is due to high atomization and ionization energy not being compensated by hydration energy.

C. Other Key Trends

• Variable O.S.: Max O.S. for Mn is +7. Sc shows only +3 (most stable).
• Magnetism: Spin-only formula: $\mu = \sqrt{n(n+2)}$ B.M.
• Catalysis: Variable O.S. allows them to form unstable intermediates (V₂O₅, Fe, Ni).

Lanthanoids (4f Series):

Ce (Z=58) to Lu (Z=71). They exhibit Lanthanoid Contraction: a steady decrease in atomic and ionic radii due to poor shielding by 4f electrons.

Actinoids (5f Series):

Th (Z=90) to Lr (Z=103). Radioactive. Wider range of oxidation states compared to lanthanoids due to smaller energy gap between 5f, 6d, and 7s levels.

K₂Cr₂O₇ (Potassium Dichromate)

Preparation: From Chromite Ore ($FeCr_2O_4$).
1. Conversion of chromite to sodium chromate.
2. Conversion of sodium chromate to sodium dichromate.
3. Conversion of sodium dichromate to potassium dichromate using KCl.

KMnO₄ (Potassium Permanganate)

Preparation: From Pyrolusite ($MnO_2$).
Alkaline oxidative fusion gives green $K_2MnO_4$, which is then oxidized (electrolytically or chemically) to purple $KMnO_4$.

• Industrial: Iron/Steel production. $V_2O_5$ in sulfuric acid manufacture.
• Daily Life: Silver compounds in photography. Copper/Zinc in alloys like brass.
• Biology: Iron in hemoglobin, Cobalt in Vitamin B12.

Color origin:

Transition metal ions are colored because d-orbitals split in the presence of ligands. Electrons jumping between these split levels absorb specific wavelengths of light (d-d transition).

• Comparison of Lanthanoid vs Actinoid contraction (Actinoid contraction is greater).
• Calculation of magnetic moment ($\mu$) for ions like $Cr^{3+}$, $Fe^{2+}$, $Mn^{2+}$.

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