The "10-Second" Questions
In JEE Mains, you have 90 questions (75 to attempt) and 180 minutes. That is 2.4 minutes per question. But wait...
A math problem might take 5 minutes. A complex physics rotation problem might take 4 minutes. Where do you save the time to solve them? You save it in Inorganic Chemistry.
Inorganic Chemistry questions are binary: You either know the answer, or you don't. There is no calculation. There is no derivation. "Which of the following is diamagnetic?" You can answer this in 10 seconds. If you master this subject, you can finish 33% of the Chemistry paper in 15 minutes, leaving you a massive time bonus for Math and Physics.
However, most students ruin this advantage by treating Inorganic Chemistry as a "Ratta" (rote learning) subject. As the best chemistry teacher for jee mains, I am here to tell you that Inorganic is 90% logic and 10% memory. In this massive guide, I will show you how to decode the NCERT, master the Periodic Table, and use Physical Chemistry concepts (like Thermodynamics and Quantum Numbers) to master Inorganic without mindless memorization.
Phase 1: The Constitution (Periodic Table)
You cannot understand the law if you haven't read the Constitution. The Periodic Table is the constitution of Chemistry.
The "Why" Behind the "What"
Students memorize trends: "Left to right size decreases." But do you know why? It is the battle between Nuclear Charge (Z) and Shielding Effect (\sigma).
Effective Nuclear Charge (Z_{eff}): This is the net pull an electron feels.
Every "exception" in Inorganic Chemistry comes from a sudden change in Shielding Effect.
Example: Why is Gallium smaller than Aluminum? Because Gallium has 10 d-electrons. d-orbitals have poor shielding. They fail to protect the outer electrons from the nucleus, so the nucleus pulls them in tighter (Lanthanoid/Scandide Contraction).
- Ionization Energy (IE): Generally increases across a period. Exception: N > O and Be > B (Half-filled and Full-filled stability).
- Electron Gain Enthalpy (\Delta H_{eg}): Chlorine has the highest negative \Delta H_{eg}, not Fluorine. Why? Because Fluorine is so small that incoming electrons feel repulsion.
- Electronegativity: Fluorine is the king (4.0). Cesium is the humblest (0.7). This difference drives bonding.
Phase 2: The Grammar (Chemical Bonding)
This is the most important chapter in the entire chemistry syllabus. It connects everything.
VSEPR Theory
Valence Shell Electron Pair Repulsion. It predicts the shape.
JEE Focus: Lone pair repulsion (lp-lp > lp-bp > bp-bp).
Question: Why is the bond angle in water (104.5^\circ) less than Methane (109.5^\circ)? Because the two lone pairs on Oxygen squeeze the bond pairs.
Molecular Orbital Theory (MOT)
This is the favorite topic of JEE Mains paper setters.
Why? Because VBT fails to explain why O_2 is paramagnetic. MOT explains it.
Trick: Master the Bond Order formula: B.O. = \frac{1}{2} (N_b - N_a). If B.O. is fractional, the species is unstable/paramagnetic. Memorize the sequence for >14e^- and \le 14e^-.
Fajan's Rule & Dipole Moment
Fajan's Rule: No bond is 100% ionic. Small cation + Large anion = High Covalent Character. (This explains why SnCl_2 is solid but SnCl_4 is liquid).
Dipole Moment: Vector addition of bond moments. NH_3 vs NF_3 is a classic JEE question.
Phase 3: The Scoring Machines
These chapters carry the highest weightage in Inorganic Chemistry.
This chapter is logical and high-scoring.
1. IUPAC Naming: Don't lose easy marks here.
2. Isomerism: Practice drawing Geometrical (cis/trans, fac/mer) and Optical isomers.
3. Crystal Field Theory (CFT): This is the core. Understand \Delta_o and Pairing Energy (P).
Satyakam Sir's Logic: Strong Field Ligands (CO, CN^-) cause pairing (Low Spin). Weak Field Ligands (Halogens, H_2O) do not (High Spin). Color arises from d-d transitions. No d-electrons? No color (Sc^{3+}, Zn^{2+}).
The "Monster" chapter. How to tame it?
Strategy: Do not read random books. Stick to NCERT.
Focus Areas:
- Group 15: Hydrides (NH_3 to BiH_3) trends in basicity, bond angle, reducing nature.
- Group 16: Structures of Oxoacids of Sulphur (H_2S_2O_8, H_2S_2O_7).
- Group 17: Interhalogen compounds (ClF_3, IF_7) structures (VSEPR application).
- Group 18: Xenon compounds (XeF_2, XeF_4, XeO_3). Their hydrolysis reactions are very important.
This is where Inorganic meets Physical Chemistry.
Ellingham Diagram: It is a graph of \Delta G vs T. It applies Thermodynamics to extraction. A metal line below can reduce the oxide of a metal line above because the net \Delta G is negative.
Ores: Memorize the formulas of common ores (Bauxite, Haematite, Copper Pyrites, Calamine). Match-the-column questions are common.
Phase 4: Practical Inorganic Chemistry
Salt Analysis is often ignored, but JEE Mains asks specific tests.
Colors and Reagents
You don't need to memorize the entire flow chart. Focus on specific, colorful tests.
1. Brown Ring Test: For Nitrate (NO_3^-). Formula: [Fe(H_2O)_5NO]^{2+}. Oxidation state of Fe is +1 (Exception!).
2. Chromyl Chloride Test: For Chloride (Cl^-). Red vapors of CrO_2Cl_2.
3. Flame Test: Colors of Alkali/Alkaline Earth metals. (Crimson Red for Li/Sr, Golden Yellow for Na, Apple Green for Ba).
4. Group Reagents: Memorize the reagents for Cation Analysis Groups 0 to 6 (dil. HCl, H_2S, etc.).
