🧪 D- AND F-BLOCK ELEMENTS HIGH-YIELD
BLUEPRINT
Lanthanoid Contraction, Chromate Profiles & Permanganate Redox Equations
This study blueprint condenses the absolute highest-priority inorganic trends, conversions, and chemical logic
from the D- and F-block chapter into direct, rule-based checklists for efficient recall.
1. Lanthanoid Contraction & Its Direct Consequences
As the atomic number increases within the 4f-series (Lanthanoids), the atomic and ionic radii exhibit a steady,
continuous decrease. This shrinkage is driven by the exceptionally poor shielding effect of 4f electrons,
enabling the rising nuclear charge to pull the outer shell inward.
The Size Equalizer Pairs: Due to this contraction, elements belonging to the 2nd (4d) and 3rd (5d) transition
series exhibit practically identical atomic radii. NTA targets these specific matching twins:
• Zr ≈ Hf (Zirconium ≈ Hafnium) — Sizes: Zr ∼ 160 pm, Hf ∼ 159 pm
• Nb ≈ Ta (Niobium ≈ Tantalum)
Basicity Trend of Hydroxides: Following Fajan's rules, covalent character grows as size decreases from
La3+ to Lu3+. Thus, the capability to release OH- drops systematically:
La(OH)3 [Most Basic] > ... > Lu(OH)3 [Least Basic]
Ionization Enthalpy Shift: The 5d elements require significantly higher ionization energy than 3d and 4d
elements because their compressed atomic clouds hold onto valence shell electrons with maximum affinity.
2. Chromate-Dichromate Interconversion (pH Dependent)
The chemical equilibrium between the tetrahedral Chromate ion (CrO4
2-) and the corner-sharing twin tetrahedral
Dichromate ion (Cr2O7
2-) in solution relies strictly on the pH of the surrounding medium:
🔄 THE PH BALANCE EQUATIONS
• In Acidic Medium (pH < 7): Yellow chromate absorbs H+ and quickly dimerizes into orange dichromate.
2CrO4
2- (Yellow) + 2H+ ⇌ Cr2O7
2- (Orange) + H2O
• In Basic Medium (pH > 7): Hydroxyl ions drive orange dichromate back down into the monomeric yellow
form.
Cr2O7
2- (Orange) + 2OH- ⇌ 2CrO4
2- (Yellow) + H2O
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NEET Inorganic Chemistry Core Series • High-Yield Master Sheet Page 1
