Some p-Block Elements — Revision Notes

⚡ 30-Second Revision

p-Block — Last electron in p-orbital, $ns^2 np^{1-6}$.
Group 13 (Boron Family) — $ns^2 np^1$. Oxidation states +3, +1 (inert pair effect for heavier elements).
Boron — Metalloid, electron deficient, Lewis acid ($BF_3$ weakest due to back-bonding), forms $B_2H_6$ (banana bonds, $sp^3$ B).
Aluminium — Metal, amphoteric ($Al_2O_3$, $Al(OH)_3$).
Borax — $Na_2B_4O_7 cdot 10H_2O$, alkaline in water, borax bead test.
Boric Acid — $H_3BO_3$, weak monobasic Lewis acid ($B(OH)_3 + H_2O \rightleftharpoons [B(OH)_4]^- + H^+$).
Group 14 (Carbon Family) — $ns^2 np^2$. Oxidation states +4, +2 (inert pair effect for heavier elements).
Carbon — Non-metal, extensive catenation, allotropes (diamond $sp^3$, graphite $sp^2$, fullerenes).
$CO$ — Neutral, poisonous, reducing agent.
$CO_2$ — Acidic, greenhouse gas.
Silicon — Non-metal, forms $SiO_2$ (acidic, 3D network), silicones ($R_2SiO$ polymers), silicates ($SiO_4^{4-}$ unit), zeolites (aluminosilicates, catalysts).

2-Minute Revision

The p-block elements, specifically Groups 13 and 14, are crucial for NEET. Group 13 (Boron family) has $ns^2 np^1$ configuration. Boron is a metalloid, forms electron-deficient compounds like diborane ($B_2H_6$) with 3-center-2-electron bonds, and acts as a Lewis acid (e.

g., $BF_3$, where Lewis acidity order is $BI_3 > BBr_3 > BCl_3 > BF_3$ due to back-bonding). Aluminium is an amphoteric metal. The inert pair effect stabilizes the +1 oxidation state for heavier elements like Thallium.

Group 14 (Carbon family) has $ns^2 np^2$ configuration. Carbon is unique for its extensive catenation and allotropy (diamond, graphite, fullerenes). Diamond is $sp^3$ hybridized and hard, while graphite is $sp^2$ hybridized and soft, conducting electricity.

The inert pair effect stabilizes the +2 oxidation state for heavier elements like Lead. Important compounds include $CO$ (neutral, poisonous), $CO_2$ (acidic), $SiO_2$ (acidic, 3D network), silicones (polymers), and silicates (based on $SiO_4^{4-}$).

Remember the anomalous behavior of the first element in each group and the diagonal relationship between Boron and Silicon.

5-Minute Revision

Let's quickly review the 'Some p-Block Elements' focusing on Groups 13 and 14. Group 13, the Boron family, has a general electronic configuration of $ns^2 np^1$. Key trends include a decrease in atomic radius from B to Al, then a slight increase for Ga (due to d-block contraction), followed by a normal increase.

Ionization enthalpy also shows irregular trends. The inert pair effect is vital here: for heavier elements like Tl, the +1 oxidation state is more stable than +3. Boron is a metalloid, forming covalent, electron-deficient compounds.

Its trihalides ($BX_3$) are Lewis acids, with the order $BI_3 > BBr_3 > BCl_3 > BF_3$ due to decreasing $ppi-ppi$ back-bonding. Diborane ($B_2H_6$) is a classic example of an electron-deficient compound with two 3-center-2-electron 'banana bonds' and $sp^3$ hybridized boron.

Aluminium is a metal, and its oxide ($Al_2O_3$) and hydroxide ($Al(OH)_3$) are amphoteric. Borax ($Na_2B_4O_7 cdot 10H_2O$) is alkaline in water and used in the borax bead test. Boric acid ($H_3BO_3$) is a weak monobasic Lewis acid, accepting $OH^-$ from water.

Moving to Group 14, the Carbon family, with $ns^2 np^2$ configuration. Metallic character increases down the group. Carbon is unique due to catenation (forming long chains/rings) and allotropy.

Diamond (3D $sp^3$ network, hard, non-conductor) and graphite (layered $sp^2$ structure, soft, conductor) are crucial. Fullerenes are molecular allotropes. The inert pair effect makes the +2 oxidation state more stable for heavier elements like Pb.

Carbon monoxide ($CO$) is a neutral, poisonous gas, while carbon dioxide ($CO_2$) is an acidic oxide. Silicon forms silicon dioxide ($SiO_2$), a 3D network solid that is acidic. Silicones are organosilicon polymers ($R_2SiO$ units) known for water repellency and thermal stability.

Silicates are based on the $SiO_4^{4-}$ tetrahedral unit, forming various structures (chain, sheet, 3D). Zeolites are aluminosilicates used as catalysts and molecular sieves. Remember the diagonal relationship between Boron and Silicon due to similar charge/radius ratios.

Prelims Revision Notes

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p-Block General Characteristics — Last electron in p-orbital. General configuration $ns^2 np^{1-6}$. Transition from metallic to non-metallic character across period.
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Group 13 (Boron Family)

* Elements: B, Al, Ga, In, Tl. Configuration $ns^2 np^1$. * Trends: Atomic radii: B < Al > Ga < In < Tl (Ga anomaly due to d-block contraction). Ionization enthalpy: Irregular trend (Ga > Al, Tl > In) due to poor d/f shielding.

Electronegativity: Irregular, Tl > In. * Oxidation States: +3 is common. +1 state stability increases down the group (inert pair effect: $Tl^+$ > $Tl^{3+}$). * Boron: Non-metal/metalloid. High IE, small size.

Forms covalent compounds. Electron deficient. Lewis acid ($BF_3$ weakest due to $ppi-ppi$ back-bonding: $BI_3 > BBr_3 > BCl_3 > BF_3$). Diagonal relationship with Si. * **Diborane ($B_2H_6$)**: Electron deficient.

Two 3-center-2-electron (banana) bonds. Four terminal 2-center-2-electron bonds. Boron is $sp^3$ hybridized. Preparation: $4BF_3 + 3LiAlH_4 \rightarrow 2B_2H_6 + 3LiF + 3AlF_3$. * **Borax ($Na_2B_4O_7 cdot 10H_2O$)**: White crystalline solid.

Hydrolyses to form alkaline solution: $Na_2B_4O_7 + 7H_2O \rightleftharpoons 2NaOH + 4H_3BO_3$. Used in borax bead test. * **Boric Acid ($H_3BO_3$)**: Weak monobasic Lewis acid. Accepts $OH^-$ from water: $B(OH)_3 + H_2O \rightleftharpoons [B(OH)_4]^- + H^+$.

* Aluminium: Metal. Amphoteric oxide ($Al_2O_3$) and hydroxide ($Al(OH)_3$). Dimeric $Al_2Cl_6$ in vapor phase/non-polar solvents.

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Group 14 (Carbon Family)

* Elements: C, Si, Ge, Sn, Pb. Configuration $ns^2 np^2$. * Trends: Metallic character increases down the group (C, Si non-metals; Ge metalloid; Sn, Pb metals). Atomic radii increase down group.

IE decreases down group. * Oxidation States: +4 is common. +2 state stability increases down the group (inert pair effect: $Pb^{2+}$ > $Pb^{4+}$). * Carbon: Non-metal. Unique catenation ability (C-C bond strong).

Allotropy: Diamond ($sp^3$, 3D network, hard, non-conductor), Graphite ($sp^2$, layered, soft, conductor), Fullerenes ($C_{60}$, cage-like). * Carbon Monoxide (CO): Neutral oxide. Highly poisonous.

Reducing agent. * **Carbon Dioxide ($CO_2$)**: Acidic oxide. Greenhouse gas. * **Silicon Dioxide ($SiO_2$)**: Acidic oxide. Covalent 3D network structure. Reacts with HF and NaOH. * Silicones: Organosilicon polymers with $R_2SiO$ units.

Water repellent, thermally stable, chemically inert. * Silicates: Basic unit $SiO_4^{4-}$ tetrahedron. Various structures (ortho, pyro, cyclic, chain, sheet, 3D). * Zeolites: Aluminosilicates, 3D network.

Used as catalysts (ZSM-5), ion exchangers, molecular sieves.

Vyyuha Quick Recall

For Boron Trihalide Lewis Acidity: Big Iodine Brings Cool Fun. (BI3 > BBr3 > BCl3 > BF3)