Lesson Plan: d and f Block Elements

Inorganic Chemistry (Class 12)

d and f Block Elements

Transition and Inner Transition elements. This chapter is less about memorizing reactions and more about explaining "Why?" (Why are they coloured? Why are they catalysts?). The concept of Lanthanoid Contraction is central to understanding the chemistry of heavier elements.

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⚠️ Prerequisites

Electronic Config: Filling of d-orbitals (Aufbau rule and exceptions like Cr, Cu).
Periodic Properties: Ionization Enthalpy and Atomic Size trends.
Redox: Oxidation states and oxidizing agents.

🧠 Study Approach

Reasoning is Key: Don't just memorize that $Zn$ is not a transition element. Understand the definition: "Incomplete d-orbitals in ground or common oxidation state".

Study Sequence

1. General Properties of d-Block

Electronic Config: $(n-1)d^{1-10}ns^{1-2}$.
Definition: Why Zn, Cd, Hg are not considered typical transition elements (Full d-orbitals).
Physical Properties: High MP/BP due to strong metallic bonding (participation of $(n-1)d$ electrons). Enthalpy of Atomization.

2. Trends in Properties (Reasoning)

Atomic Size: Decreases across period, but constant towards end (shielding).
Ionization Enthalpy: Irregular trend due to stability of $d^0, d^5, d^{10}$.
Oxidation States: Variable states due to comparable energy of $ns$ and $(n-1)d$. Highest O.S. shown by Mn (+7).

3. Standard Electrode Potentials ($E^\circ$)

Trends in $M^{2+}/M$ values.
Why is $E^\circ$ for $Cu$ positive (+0.34V)? (High enthalpy of atomization and low hydration enthalpy). Why is $E^\circ$ for $Mn^{3+}/Mn^{2+}$ highly positive?

4. Magnetic & Catalytic Properties

Magnetic: Para vs Diamagnetic. Spin only magnetic moment $\mu = \sqrt{n(n+2)}$ BM.
Coloured Ions: d-d transition. Conditions for colour (unpaired d-electrons).
Catalytic: Ability to change oxidation state and surface area.

5. Important Compounds

Potassium Dichromate ($K_2Cr_2O_7$): Preparation from Chromite ore. Effect of pH (Chromate $\leftrightarrow$ Dichromate equilibrium). Oxidizing action.
Potassium Permanganate ($KMnO_4$): Preparation from Pyrolusite ore. Oxidizing action in Acidic ($Mn^{2+}$), Neutral ($MnO_2$), and Basic ($MnO_4^{2-}$) media.

6. Lanthanoids (4f Series)

Electronic Config: $4f^{1-14}5d^{0-1}6s^2$.
Lanthanoid Contraction: Steady decrease in atomic size due to poor shielding of 4f electrons. Consequences: Similarity of Zr/Hf (4d/5d series).
Oxidation States: +3 is dominant. Ce(+4) is oxidizing, Eu(+2) is reducing.

7. Actinoids (5f Series)

Greater range of oxidation states than lanthanoids (due to comparable energy of 5f, 6d, 7s). Actinoid contraction (greater than lanthanoid contraction due to poorer shielding by 5f).

🎯 How to Practice

Reasoning Drills: Write down 1-line answers for: Why is Zn not a transition metal? Why is $Sc^{3+}$ colourless? Why does Zr and Hf have same size?

Balancing Redox: Practice balancing ionic equations for $MnO_4^-$ reacting with $Fe^{2+}$, $C_2O_4^{2-}$, and $I^-$ in acidic medium. Memorize the product ($Mn^{2+}$).

Config check: Write electronic configurations for $Cr$, $Cu$, $La$, $Gd$, and $Ce$. These are the common exceptions asked in exams.

📝 Quick Revision Notes

Spin Only Magnetic Moment $$\mu = \sqrt{n(n+2)} \text{ BM}$$

(n = number of unpaired electrons)

Chromate-Dichromate pH effect

$2CrO_4^{2-} (\text{Yellow}) + 2H^+ \to Cr_2O_7^{2-} (\text{Orange}) + H_2O$
Acidic $\to$ Dichromate. Basic $\to$ Chromate.

KMnO4 Equivalent Mass

Acidic: $MnO_4^- \xrightarrow{5e^-} Mn^{2+}$ (Eq wt = M/5)
Neutral: $MnO_4^- \xrightarrow{3e^-} MnO_2$ (Eq wt = M/3)
Basic: $MnO_4^- \xrightarrow{1e^-} MnO_4^{2-}$ (Eq wt = M/1)

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