Exam Master Review Sheet - d & f Block Elements

CHEMCA

EXAM MASTER FORMULA SHEET

d and f Block Elements

High-Yield Inorganic Synthesis & Trends (JEE & NEET)

1. Transition Elements (d-block)

Elements having partially filled d-orbitals in their ground state or in any common oxidation state.

General Configuration

\[ (n-1)d^{1-10} ns^{1-2} \]

* $\ce{Zn, Cd, Hg}$ are NOT considered transition elements because they have completely filled $d^{10}$ subshells in ground & common oxidation states.

Oxidation States

Variable OS due to small energy difference between $(n-1)d$ and $ns$ orbitals.

• Maximum OS increases up to the middle of the series.
• Highest OS: $\ce{Os (+8)}$ and $\ce{Ru (+8)}$.
• 3d Series Max: $\ce{Mn (+7)}$.
• Low OS are stabilizing by $\pi$-acceptor ligands ($\ce{CO}$).

Atomic Radii Trends (3d Series)

Sc to Mn (Decreases) $Z_{eff}$ increases, overpowering the weak shielding of added d-electrons.

Fe, Co, Ni (Constant) Increase in $Z_{eff}$ is perfectly balanced by the shielding of d-electrons.

Cu to Zn (Increases) Electron-electron repulsion in completely filled d-orbitals outweighs $Z_{eff}$.

2. Magnetic, Spectral & Catalytic Properties

Magnetic Moment ($\mu$):

\[ \mu = \sqrt{n(n+2)} \text{ B.M.} \]

$n$ = Number of unpaired electrons. B.M. = Bohr Magneton.
Paramagnetic: $n \ge 1$. Diamagnetic: $n = 0$.

Color in Transition Metal Ions

• • d-d Transitions: Excitation of electrons between split d-orbitals. Requires unpaired electrons.
  $\ce{Sc^{3+}, Ti^{4+}, Zn^{2+}, Cu^+}$ are Colorless.
• • Ligand-to-Metal Charge Transfer (LMCT): Occurs in $d^0$ ions with high oxidation states.
  Why $\ce{KMnO4}$ (Purple) and $\ce{K2Cr2O7}$ (Orange) are deeply colored despite $d^0$ config!

Catalytic Nature

Excellent catalysts due to their ability to adopt variable oxidation states (providing alternate pathways) and large surface area for adsorption.
• Haber Process: $\ce{Fe}$ | Contact Process: $\ce{V2O5}$ | Hydrogenation: $\ce{Pd/Pt/Ni}$

Interstitial Compounds & Alloys

Interstitial: Small non-metals ($H, C, N$) trapped in the metallic crystal lattice. Non-stoichiometric. Very hard, chemically inert, retain conductivity.
Alloys: Formed readily because atomic radii of transition metals are very similar (within 15%).

3. Key Compounds: $\ce{K2Cr2O7}$ & $\ce{KMnO4}$

Potassium Dichromate ($\ce{K2Cr2O7}$)

Preparation from Chromite Ore ($\ce{FeCr2O4}$):

1. $\ce{4FeCr2O4 + 8Na2CO3 + 7O2 -> 8Na2CrO4 + 2Fe2O3 + 8CO2}$ (Yellow sol.)
2. $\ce{2Na2CrO4 + 2H+ -> Na2Cr2O7 + 2Na+ + H2O}$ (Orange sol.)
3. $\ce{Na2Cr2O7 + 2KCl -> K2Cr2O7 v + 2NaCl}$ (Crystallizes out)

Chromate-Dichromate Equilibrium:

\[ \ce{2CrO4^{2-} \text{ (Yellow)} + 2H+ <=> Cr2O7^{2-} \text{ (Orange)} + H2O} \]

pH dependent! Acidic $\to$ Orange | Basic $\to$ Yellow

Oxidizing Action (Acidic Medium):

\[ \ce{Cr2O7^{2-} + 14H+ + 6e- -> 2Cr^{3+} + 7H2O} \quad (E^\circ = 1.33V) \]

Oxidizes: $\ce{Fe^{2+} \to Fe^{3+}}$, $\ce{I^- \to I2}$, $\ce{H2S \to S}$

Potassium Permanganate ($\ce{KMnO4}$)

Preparation from Pyrolusite Ore ($\ce{MnO2}$):

1. $\ce{2MnO2 + 4KOH + O2 -> 2K2MnO4 + 2H2O}$ (Dark green manganate)
2. $\ce{3MnO4^{2-} + 4H+ -> 2MnO4^- + MnO2 + 2H2O}$ (Disproportionation in acid/neutral)

Oxidizing Action (Depends on Medium):

Medium	Half-Reaction	n-factor
Acidic	$\ce{MnO4^- + 8H+ + 5e- -> Mn^{2+} + 4H2O}$	5
Neutral / Faintly Basic	$\ce{MnO4^- + 2H2O + 3e- -> MnO2 v + 4OH-}$	3
Strongly Basic	$\ce{MnO4^- + e- -> MnO4^{2-}}$	1

*In Acidic medium: $\ce{I^- \to I2}$. *In Neutral/Alkaline medium: $\ce{I^- \to IO3^-}$ (Iodate).

4. f-block Elements (Inner Transition)

General Electronic Configuration

\[ (n-2)f^{1-14} (n-1)d^{0-1} ns^2 \]

Lanthanoids (4f series, $n=6$) and Actinoids (5f series, $n=7$).

Lanthanoid Contraction:

Cause:

Poor shielding effect of 4f-electrons leads to a steady decrease in atomic and ionic radii with increasing atomic number.

Consequences:

• Similarity in 4d and 5d series radii ($Zr \approx Hf$, $Nb \approx Ta$).
• Difficulty in separation of Lanthanoids (similar chemical properties).
• Decrease in basic strength: $\ce{La(OH)3}$ is most basic, $\ce{Lu(OH)3}$ is least basic (due to increasing covalent character / Fajans' rule).

Actinoid Contraction:

Actinoids show a contraction similar to lanthanoids. However, the Actinoid contraction is greater from element to element than the lanthanoid contraction.

Reason: 5f electrons have poorer shielding effect compared to 4f electrons.

5. Comparative Study (Ln vs Ac)

Feature	Lanthanoids (4f Series)	Actinoids (5f Series)
Principal Oxidation State	+3	+3
Other Oxidation States	+2 and +4 are rare (shown if $f^0, f^7, f^{14}$)	Show a wide range (+4, +5, +6, +7) due to comparable energies of 5f, 6d, 7s.
Radioactivity	Only Promethium (Pm) is radioactive.	All elements are Radioactive.
Oxo-cations Formation	Do not form oxo-cations.	Readily form oxo-cations like $\ce{UO2^{2+}, PuO2^{2+}}$.
Complex Formation	Less tendency to form complexes.	Greater tendency to form complexes.

Mischmetal: A well-known alloy consisting of Lanthanoid metals (~95%) and Iron (~5%), with traces of S, C, Ca, Al. Used in magnesium-based bullets, shells, and lighter flints.

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