CHEMCA
EXAM MASTER REVIEW SHEET
Chemical Bonding & Molecular Structure
High-Yield Revision for JEE Main, Advanced & NEET
1. Ionic Bonding & Lattice Energy
Lattice Energy (\(U\)):
\[ U \propto \frac{z^+ z^-}{r^+ + r^-} \]
Directly proportional to charges, inversely to inter-ionic distance.
Born-Haber Cycle
\(\Delta H_f = S + \frac{1}{2}D + IE + EA + U\)
S: Sublimation, D: Dissociation, IE: Ionization, EA: Electron Affinity
Fajan's Rules (Covalent Character)
Covalent character \(\uparrow\) if:
- Small Cation, Large Anion
- High Charge on either ion
- Pseudo-noble gas configuration (\(ns^2 np^6 nd^{10}\))
2. Valence Bond Theory & Hybridization
Steric Number (\(Z\)) Calculation:
\[ Z = \frac{1}{2} [V + M - C + A] \]
\(V\): Valence \(e^-\) (Central)
\(M\): Monovalent atoms
\(C\): Cationic charge
\(A\): Anionic charge
| \(Z\) | Hybridization | Geometry | Bond Angle |
|---|---|---|---|
| 2 | \(sp\) | Linear | 180° |
| 3 | \(sp^2\) | Trigonal Planar | 120° |
| 4 | \(sp^3\) | Tetrahedral | 109°28' |
| 5 | \(sp^3d\) | Trigonal Bipyramidal | 90°, 120° |
| 6 | \(sp^3d^2\) | Octahedral | 90° |
3. VSEPR Theory (Shapes)
Repulsion Order:
lp - lp > lp - bp > bp - bp
Dipole Moment (\(\mu\)):
\[ \mu = q \times d \]
Unit: Debye (D). \(1 \text{ D} = 3.33 \times 10^{-30} \text{ C m}\)
Formal Charge (F.C.):
\[ [V] - [L] - \frac{1}{2}[S] \]
V: Valence, L: Lone pair \(e^-\), S: Shared \(e^-\)
4. Molecular Orbital Theory
Bond Order (B.O.):
\[ \text{B.O.} = \frac{N_b - N_a}{2} \]
B.O. \(\propto\) Bond Strength \(\propto 1/\text{Bond Length}\)
Electronic Config. (upto \(N_2\)):
\(\sigma 1s < \sigma^* 1s < \sigma 2s < \sigma^* 2s < (\pi 2p_x = \pi 2p_y) < \sigma 2p_z \dots\)
For \(O_2, F_2\):\(\dots < \sigma 2p_z < (\pi 2p_x = \pi 2p_y) \dots\)
Magnetic Nature: If unpaired electrons exist \(\implies\) Paramagnetic. If all paired \(\implies\) Diamagnetic.
5. Hydrogen Bonding
Intermolecular H-bond
Between different molecules. Increases B.P., Solubility, and Viscosity. (e.g., \(H_2O, NH_3, HF\))
Intramolecular H-bond
Within the same molecule (Chelation). Decreases B.P. and Solubility. (e.g., o-nitrophenol)
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