CHEMCA
EXAM MASTER FORMULA SHEET
The p-Block Elements (Groups 13-18)
1. General Characteristics & Key Effects
The reluctance of $ns^2$ valence electrons to participate in bonding due to poor shielding by intervening $d$ and $f$ orbitals. As we go down the group, the lower oxidation state becomes more stable.
The first element of each group (B, C, N, O, F) behaves differently from the rest of its group members due to:
- Smallest size & high electronegativity.
- High ionization enthalpy.
- Absence of vacant d-orbitals: Restricts their maximum covalency to 4 (e.g., $\ce{BF4-}$ exists, but $\ce{BF6^3-}$ does not).
2. Group 13 (Boron) & Group 14 (Carbon)
An electron-deficient dimer. Boron is $sp^3$ hybridized.
$2 \times (\ce{B-H-B})$ bridge bonds ($3c-2e$)
Banana bonds restrict rotation. Terminal atoms are coplanar.
- • Orthoboric Acid ($\ce{H3BO3}$): A weak monobasic Lewis acid. It does not donate a proton; it accepts an $\ce{OH-}$ from water: $\ce{B(OH)3 + 2H2O <=> [B(OH)4]- + H3O+}$.
- • Borazine ($\ce{B3N3H6}$): Inorganic benzene. Isoelectronic and isostructural with benzene, but more reactive due to bond polarity.
- • Diamond: $sp^3$ hybridized, rigid 3D network, hardest natural substance, electrical insulator.
- • Graphite: $sp^2$ hybridized, layered structure held by van der Waals forces. Good conductor (free $\pi$ electrons), acts as a lubricant.
- • Fullerenes: E.g., $\ce{C60}$. Contains 20 six-membered rings and 12 five-membered rings. Purest form of carbon.
- • Silicates: Basic structural unit is $\ce{SiO4^4-}$ (tetrahedral).
- • Silicones: Synthetic organosilicon polymers containing $\ce{R2SiO}$ repeating units. Highly water-repellent (hydrophobic) and thermally stable.
3. Group 15 (Pnictogens)
Group 15$\ce{Conc. -> NO2 (g)}$
$\ce{Conc. -> NO2 (g)}$
- Haber's Process ($\ce{NH3}$):
$\ce{N2 + 3H2 <=>[Fe / Mo][700K, 200 atm] 2NH3}$ - Ostwald's Process ($\ce{HNO3}$):
Catalytic oxidation of $\ce{NH3}$ over $Pt/Rh$ gauge at 500K to yield $\ce{NO}$, which is oxidized to $\ce{NO2}$ and dissolved in water.
| Formula & Name | Ox. State | Bonds | Basicity | Reducing Nature |
|---|---|---|---|---|
| $\ce{H3PO2}$ (Hypophosphorous) | +1 | $1 (\ce{P=O}), 1 (\ce{P-OH}), \mathbf{2 (\ce{P-H})}$ | Monobasic | Strong |
| $\ce{H3PO3}$ (Orthophosphorous) | +3 | $1 (\ce{P=O}), 2 (\ce{P-OH}), \mathbf{1 (\ce{P-H})}$ | Dibasic | Moderate |
| $\ce{H3PO4}$ (Orthophosphoric) | +5 | $1 (\ce{P=O}), 3 (\ce{P-OH}), \mathbf{0 (\ce{P-H})}$ | Tribasic | Non-reducing |
Note: Basicity = Number of $\ce{P-OH}$ bonds. Reducing character = Number of $\ce{P-H}$ bonds.
4. Group 16 (Chalcogens)
Group 16- • $\ce{H2SO4}$ (Sulphuric Acid): Oil of Vitriol. Manufactured via Contact Process ($\ce{V2O5}$ catalyst).
- • $\ce{H2S2O7}$ (Oleum): Pyrosulphuric acid. Contains $\ce{S-O-S}$ linkage.
- • $\ce{H2SO5}$ (Caro's Acid): Peroxymonosulphuric acid. Has one peroxy ($\ce{-O-O-}$) linkage.
- • $\ce{H2S2O8}$ (Marshall's Acid): Peroxydisulphuric acid. Has one peroxy ($\ce{-O-O-}$) linkage.
5. Group 17 (Halogens)
Group 17Electron Gain Enthalpy
Bond Dissoc. Enthalpy
$\ce{F2}$ has low BDE and low EGE due to intense e-e repulsions in its small 2p orbitals.
Geometry e.g., $\ce{ClF3}$ (T-shaped), $\ce{IF7}$ (Pentagonal bipyramidal).
6. Group 18 (Noble Gases)
Group 18| Compound | Geometry (VSEPR) | Hybridization |
|---|---|---|
| $\ce{XeF2}$ | Linear (3 l.p.) | $sp^3d$ |
| $\ce{XeF4}$ | Square Planar (2 l.p.) | $sp^3d^2$ |
| $\ce{XeF6}$ | Distorted Octahedral (1 l.p.) | $sp^3d^3$ |
| $\ce{XeO3}$ | Pyramidal (1 l.p.) | $sp^3$ |
| $\ce{XeOF4}$ | Square Pyramidal (1 l.p.) | $sp^3d^2$ |
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