Chemistry Basics – Advanced University‑Level Study Notes
Prepared for NABARD Grade‑A (General Awareness & Current Affairs)
Why These Notes?
In competitive exams, “General Awareness” often includes science facts, breakthroughs, and policy‑relevant concepts.
Mastery of first‑principles chemistry equips you to interpret news on green chemistry, pharmaceuticals, energy storage, etc., with analytical depth and confidence.
1. Atomic Structure – From Quantum Mechanics to the Periodic Table
| Concept | First‑Principles Derivation | Key Take‑aways |
|---|---|---|
| Schrödinger Equation | ( \hat{H}\psi = E\psi ) for an electron in a Coulomb potential. Solutions → Hydrogenic orbitals (\psi_{n\ell m}). | Energy quantization; orbital shapes; basis for chemical bonding. |
| Pauli Exclusion & Hund's Rule | No two fermions share identical quantum numbers; maximize spin multiplicity. | Determines electronic configuration and magnetic properties. |
| Electron Configuration | Fill orbitals by increasing (n+\ell), then (n). | Explains periodic trends. |
| Nuclear Binding Energy | (E_b = Z m_p + N m_n - M_{\text{atom}}) (mass defect). | Stability of isotopes; explains alpha decay, fission/fusion energetics. |
Edge Cases
- Metastable Isotopes: Half‑lives from seconds to billions of years.
- Superheavy Elements (Z>118): Relativistic effects alter orbital energies.
2. Periodic Table – Trends and Exceptions
| Trend | Quantum‑Mechanical Basis | Observed Trend | Exceptions |
|---|---|---|---|
| Electronegativity | Electron affinity + ionization energy | ↑ across period, ↓ down group | Halogens (high), Noble gases (low but measurable) |
| Ionization Energy | Energy to remove valence electron | ↑ across, ↓ down | d‑block elements show irregularities due to shielding |
| Atomic Radius | Outer electron cloud extent | ↓ across, ↑ down | Lanthanide contraction reduces radius of early 4f elements |
| Electron Affinity | Energy released on gaining an electron | ↑ across, ↓ down | Transition metals have variable affinities |
Graphical representation: Include a periodic trend diagram with highlighted anomalies (e.g., sodium vs magnesium, phosphorus vs sulfur).
3. Chemical Bonding – From Valence to Valence Bond Theory
3.1 Classical Picture
- Ionic Bond: Full electron transfer → Coulombic attraction.
- Covalent Bond: Shared electron pair.
3.2 Quantum–Mechanical Picture
- Molecular Orbital (MO) Theory: Combine atomic orbitals (AO) → σ, π, δ MOs.
- LCAO (Linear Combination of Atomic Orbitals): (\psi_{\text{MO}} = \sum c_i \psi_i).
- Bond Order: (\frac{(n_{\text{bonding}}-n_{\text{antibonding}})}{2}).
3.3 Hybridization & Resonance
- sp, sp², sp³, sp³d, sp³d²: Determines geometry (tetrahedral, trigonal planar, etc.).
- Resonance: Delocalization across multiple structures → lower energy.