🧱 p-Block Elements (Groups 13–18)

The p-block exhibits remarkable structural diversity—from electron-deficient multi-center boranes to hypervalent noble gas fluorides. Key competitive exam topics include inert pair effect oxidation state stabilities, oxyacid structural basicities, silicate chain and sheet topology, and Xenon fluoride hydrolysis stoichiometry.

1. 🔒 The Inert Pair Effect

As we descend Groups 13, 14, and 15, the intervening filled $d$ and $f$ subshells shield nuclear charge poorly, causing the valence $n s^{2}$ electrons to be held tightly by the nucleus ("inert"):

Lower oxidation state becomes progressively MORE stable down the group

Group 13: $+ 3$ stability: $B > A l > G a > I n > T l$ ; $+ 1$ stability: $T l > I n > G a > A l > B$ .
- $T l^{3 +}$ is a powerful oxidizing agent ( $T l^{3 +} + 2 e^{-} \to T l^{+}$ ).
Group 14: $+ 4$ stability: $C > S i > G e > S n > P b$ ; $+ 2$ stability: $P b > S n > G e > S i$ .
- $P b O_{2}$ is a strong oxidizing agent; $S n^{2 +}$ is a reducing agent ( $S n^{2 +} \to S n^{4 +} + 2 e^{-}$ ).
Group 15: $+ 5$ stability: $N > P > A s > S b > B i$ ; $+ 3$ stability: $B i > S b > A s > P > N$ .
- $B i_{2} O_{5}$ is unstable; $B i^{5 +}$ acts as a strong oxidizing agent.

2. 🧪 Group 13: Boron Compounds & Diborane

2.1 Diborane ( $B_{2} H_{6}$ ) Structure & Reactions

Each Boron is $s p^{3}$ hybridized. Contains four terminal $B - H$ bonds ( $2 c - 2 e$ , length $1.19 \AA$ ) and two bridging $B - H - B$ bonds ( $3 c - 2 e$ banana bonds, length $1.33 \AA$ ).
Reaction with Ammonia ( $N H_{3}$ ):
- Low temperature ( $1 : 2$ ratio): Symmetrical cleavage gives $[B H_{2} (N H_{3})_{2}]^{+} [B H_{4}]^{-}$ .
- High temperature ( $1 : 2$ ratio heated to $200^{\circ} C$ ): Yields Borazine ("Inorganic Benzene") $B_{3} N_{3} H_{6}$ : $3 B_{2} H_{6} + 6 N H_{3} \overset{Δ}{\to} 2 B_{3} N_{3} H_{6} + 12 H_{2}$
- Borazine is isoelectronic and isostructural with Benzene, but more reactive due to $B^{δ +} - N^{δ -}$ bond polarity (undergoes electrophilic additions without catalyst).

3. 🌲 Group 14: Silicones & Silicates

3.1 Silicate Mineral Classification (Based on Shared $[S i O_{4}]^{4 -}$ Tetrahedral Corners)

Silicate Type	Fundamental Anion Formula	Shared Oxygens per Tetrahedron	Examples
Orthosilicates (Nesosilicates)	$[S i O_{4}]^{4 -}$	$0$ (Isolated tetrahedra)	Forsterite ( $M g_{2} S i O_{4}$ ), Phenacite ( $B e_{2} S i O_{4}$ ), Zircon ( $Z r S i O_{4}$ )
Pyrosilicates (Sorosilicates)	$[S i_{2} O_{7}]^{6 -}$	$1$	Thortveitite ( $S c_{2} S i_{2} O_{7}$ ), Hemimorphite
Cyclic / Ring Silicates	$[S i_{3} O_{9}]^{6 -}$ or $[S i_{6} O_{18}]^{12 -}$	$2$	Beryl ( $B e_{3} A l_{2} S i_{6} O_{18}$ ), Benitoite ( $B a T i S i_{3} O_{9}$ )
Chain Silicates (Pyroxenes)	$[(S i O_{3})_{n}]^{2 n -}$	$2$ (Linear single chain)	Diopside ( $C a M g (S i O_{3})_{2}$ ), Spodumene ( $L i A l (S i O_{3})_{2}$ )
Double Chain (Amphiboles)	$[(S i_{4} O_{11})_{n}]^{6 n -}$	Alternate $2$ and $3$	Asbestos, Tremolite
Sheet Silicates (Phyllosilicates)	$[(S i_{2} O_{5})_{n}]^{2 n -}$	$3$ (2D infinite sheets)	Talc ( $M g_{3} (S i_{2} O_{5})_{2} (O H)_{2}$ ), Mica, Kaolinite
3D Framework (Tektosilicates)	$[(S i O_{2})_{n}]$	$4$ (All four corners shared)	Quartz, Feldspar, Zeolites

4. ⚡ Group 15 & 16: Oxyacids of Phosphorus & Sulfur

4.1 Oxyacids of Phosphorus

Oxyacid	Formula	Oxidation State of P	Basicity ( $P - O H$ )	$P - H$ Bonds (Reducing)	$P = O$ Bonds
Hypophosphorous (Phosphinic)	$H_{3} P O_{2}$	$+ 1$	1 (Monobasic)	2 (Strong reducing agent)	1
Phosphorous (Phosphonic)	$H_{3} P O_{3}$	$+ 3$	2 (Dibasic)	1 (Reducing agent)	1
Orthophosphoric	$H_{3} P O_{4}$	$+ 5$	3 (Tribasic)	0 (Non-reducing)	1
Pyrophosphoric	$H_{4} P_{2} O_{7}$	$+ 5$	4 (Tetrabasic)	0 ( $1 \times P - O - P$ bridge)	2

4.2 Oxyacids of Sulfur: Marshall's Acid & Caro's Acid

Caro's Acid ( $H_{2} S O_{5}$ , Peroxomonosulfuric acid): Contains one peroxide linkage ( $- O - O -$ ). O.S. of Sulfur is $+ 6$ (NOT $+ 8$ !).
Marshall's Acid ( $H_{2} S_{2} O_{8}$ , Peroxodisulfuric acid): Structure $H O - S O_{2} - O - O - S O_{2} - O H$ . O.S. of both Sulfur atoms is $+ 6$ .

5. 💎 Group 18: Xenon Compounds & Hydrolysis

5.1 Preparation & Hydrolysis of Xenon Fluorides

$X e + F_{2} \overset{673 K, 1 bar}{\to} X e F_{2}$ ( $1 : 1$ ratio)
$X e + 2 F_{2} \overset{873 K, 7 bar}{\to} X e F_{4}$ ( $1 : 5$ ratio)
$X e + 3 F_{2} \overset{573 K, 60 - 70 bar}{\to} X e F_{6}$ ( $1 : 20$ ratio)

Hydrolysis Stoichiometry:

$X e F_{2}$ (Redox Hydrolysis): $2 X e F_{2} + 2 H_{2} O \to 2 X e ↑ + 4 H F + O_{2} ↑$
$X e F_{4}$ (Disproportionation Hydrolysis): $6 X e F_{4} + 12 H_{2} O \to 2 X e O_{3} + 4 X e ↑ + 24 H F + 3 O_{2} ↑$
$X e F_{6}$ (Complete Non-Redox Hydrolysis): $X e F_{6} + 3 H_{2} O \to X e O_{3} + 6 H F$
- Partial hydrolysis: $X e F_{6} + H_{2} O \to X e O F_{4} + 2 H F$ ; $X e F_{6} + 2 H_{2} O \to X e O_{2} F_{2} + 4 H F$ .

🧱 p-Block Elements (Groups 13–18) ​

1. 🔒 The Inert Pair Effect ​

2. 🧪 Group 13: Boron Compounds & Diborane ​

2.1 Diborane (B2H6) Structure & Reactions ​

3. 🌲 Group 14: Silicones & Silicates ​

3.1 Silicate Mineral Classification (Based on Shared [SiO4]4− Tetrahedral Corners) ​

4. ⚡ Group 15 & 16: Oxyacids of Phosphorus & Sulfur ​

4.1 Oxyacids of Phosphorus ​

4.2 Oxyacids of Sulfur: Marshall's Acid & Caro's Acid ​

5. 💎 Group 18: Xenon Compounds & Hydrolysis ​

5.1 Preparation & Hydrolysis of Xenon Fluorides ​

Hydrolysis Stoichiometry: ​