The p-Block Elements

This block contains metals, non-metals, and metalloids. The chemistry is vast, but it is governed by predictable trends like the Inert Pair Effect and the ability of second-period elements ($C, N, O$) to form $p\pi-p\pi$ multiple bonds.

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⚠️ Prerequisites

Periodic Trends: Atomic size, Ionization Enthalpy, Electronegativity.
Chemical Bonding: VSEPR theory (crucial for Xenon/Interhalogen compounds).
Redox: Oxidation states and Disproportionation.

🧠 Study Approach

Anomalous Behavior: The first element of every group (B, C, N, O, F) behaves differently due to small size, high electronegativity, and absence of d-orbitals. Focus on these anomalies.

Study Sequence

1. General Trends (Groups 13-18)

Inert Pair Effect: Reluctance of s-electrons to bond. Stability of lower oxidation state increases down the group ($Tl^+ > Tl^{3+}$, $Pb^{2+} > Pb^{4+}$, $Bi^{3+} > Bi^{5+}$).
Catenation: Self-linking property ($C >> Si > Ge \approx Sn$).

2. Boron & Carbon Families (G13, G14)

Boron: Diborane ($B_2H_6$) structure (Banana bond/3c-2e bond). Boric Acid ($H_3BO_3$) layered structure.
Carbon: Allotropes (Diamond, Graphite, Fullerenes).
Silicon: Silicones (R-substituted siloxanes) and Silicates (structural units).

3. Nitrogen Family (G15)

$N_2$: Inertness (Triple bond).
Ammonia ($NH_3$): Haber Process. Basic nature (Lone pair).
Nitric Acid ($HNO_3$): Ostwald Process. Oxidizing agent (reacts with Cu/Zn differently depending on conc).
Phosphorus: White vs Red P. $PH_3$ (Phosphine). $PCl_3$ vs $PCl_5$ structures.

4. Oxygen Family (G16)

Anomalous O: Hydrogen bonding in $H_2O$.
Sulphur: Rhombic vs Monoclinic. $SO_2$ properties.
Sulphuric Acid ($H_2SO_4$): Contact Process. Dehydrating agent and Oxidizing agent.
Oxoacids of S: Structures of $H_2SO_3, H_2SO_4, H_2S_2O_8$ (Peroxo linkage), $H_2S_2O_7$ (Oleum).

5. Halogens (G17)

Trends: Bond dissociation enthalpy ($Cl_2 > Br_2 > F_2 > I_2$). Why $F_2$ is weak? (Repulsion). Electron Gain Enthalpy ($Cl > F$).
Chlorine: Deacon's Process. Bleaching action (Oxidation).
Interhalogens: $XX', XX'_3, XX'_5, XX'_7$. Why are they more reactive than pure halogens? (Weaker bond).

6. Noble Gases (G18)

Why Reactivity? Bartlett's discovery ($O_2^+[PtF_6]^-$ $\to$ $Xe^+[PtF_6]^-$). Ionization energy of Xe $\approx$ $O_2$.
Xenon Compounds: $XeF_2, XeF_4, XeF_6$ (Preparation and Hydrolysis).
Structures (VSEPR): Linear, Square Planar, Distorted Octahedral, Pyramidal ($XeO_3$).

🎯 How to Practice

Draw Structures: Do not just look at them. Draw $XeF_2, XeF_4, XeO_3, PCl_5, SF_4, H_2SO_4, H_2S_2O_8$. Count the lone pairs and bond pairs for VSEPR prediction.

Reasoning Cards: Make flashcards for: "Why $H_2O$ liquid/$H_2S$ gas?", "Why $N_2$ inert?", "Why $Bi(V)$ strong oxidant?", "Why $F_2$ has low bond enthalpy?".

Reaction Products: Focus on reaction of $Cl_2$ with NaOH (Cold/Dilute vs Hot/Conc). Reaction of $HNO_3$ with C, S, Zn, Cu.

📝 Quick Revision Notes

Xenon Hydrolysis

$XeF_2 + H_2O \to Xe + HF + O_2$
$XeF_4 + H_2O \to Xe + XeO_3 + HF + O_2$ (Disproportionation)
$XeF_6 + 3H_2O \to XeO_3 + 6HF$ (Complete hydrolysis)

Reducing Character of P-Acids

Depends on number of P-H bonds.
$H_3PO_2$ (2 P-H, Strong) > $H_3PO_3$ (1 P-H) > $H_3PO_4$ (0 P-H, Non-reducing).

Hydrides Boiling Point

$H_2O \gg H_2Te > H_2Se > H_2S$
$NH_3$ (H-bond) vs $PH_3$ (lowest BP)

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Lesson Plan: p-Block Elements (G13-18)