Chemistry Basics – Study Notes for Puducherry PSC
General Awareness & Current Affairs
Exam‑oriented, rigorous, derivations & practice problem
1. Introduction
Chemistry is the backbone of many subjects in the Puducherry PSC syllabus. A solid grasp of the fundamentals—atomic structure, periodic trends, bonding, thermodynamics, kinetics, equilibrium, and current research—will help you score high in the competitive exam.
2. Atomic Structure
| Concept | Key Points | Formula / Relation |
|---|---|---|
| Subatomic particles | Protons (+), neutrons (0), electrons (–). | — |
| Atomic number (Z) | Number of protons. | Z = Nₑ (number of electrons in a neutral atom) |
| Mass number (A) | Protons + neutrons. | A = Z + Nₙ |
| Isotopes | Same Z, different Nₙ. | Example: C‑12 (Z=6, Nₙ=6), C‑14 (Z=6, Nₙ=8) |
| Quantum numbers | n, l, mₗ, s (principal, azimuthal, magnetic, spin). | Energy levels: (E_n = -\frac{Z^2 R_H}{n^2}) |
| Electron configuration | Aufbau principle, Pauli exclusion, Hund’s rule. | e.g., Na: 1s² 2s² 2p⁶ 3s¹ |
Derivation – Bohr Radius
Starting from Coulomb’s law and centripetal force balance:
[ \frac{Z e^2}{4\pi \epsilon_0 r^2} = \frac{m_e v^2}{r} ]
Using Bohr’s quantization (m_e v r = n\hbar) → solve for (r):
[ r_n = \frac{4\pi \epsilon_0 \hbar^2}{m_e e^2}\frac{n^2}{Z} ]
The constant (a_0 = 5.29\times10^{-11}) m is the Bohr radius for hydrogen.
3. Periodic Table & Trends
| Trend | Direction | Reason |
|---|---|---|
| Atomic radius | ↓ ↓ | More shells → larger radius |
| Ionization energy (IE) | ↑ ↑ | Greater nuclear attraction |
| Electron affinity | ↑ ↑ | Fewer electrons to repel |
| Electronegativity | ↑ ↑ | Same as IE trend |
Tricky Point – noble gas configuration leads to very high IE and low electron affinity.
4. Chemical Bonding
| Bond Type | Characteristics | Key Formula |
|---|---|---|
| Ionic |