Important Rules of Inorganic Chemistry

 📘 Important Rules of Inorganic Chemistry

🔹 1. Periodic Table Rules (Periodicity)

Understanding trends in the periodic table is key.

Atomic Size:

↓ across a period (left to right)

↑ down a group

Ionization Energy:

↑ across a period

↓ down a group

Electronegativity:

Increases across a period

Decreases down a group

Metallic Character:

Decreases across a period

Increases down a group

🔸 Trick: Left and down = more metallic and reactive metals

Right and up = more electronegative and non-metallic

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🔹 2. Oxidation Number Rules

Used in redox reactions and naming.

1. Elements in their elemental state = 0

→ e.g. Na, Cl₂, O₂ = 0

2. Group 1 = +1, Group 2 = +2

3. Oxygen = usually −2 (except in peroxides = −1, OF₂ = +2)

4. Hydrogen = +1 (with non-metals), −1 (with metals)

5. Fluorine = always −1

6. The sum of oxidation numbers = overall charge of the molecule or ion

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🔹 3. Acid-Base Theories

Arrhenius: Acids produce H⁺, bases produce OH⁻ in water

Brønsted–Lowry: Acid = proton donor, Base = proton acceptor

Lewis: Acid = electron pair acceptor, Base = electron pair donor

🧪 Example:

NH₃ + H⁺ → NH₄⁺ (NH₃ is a base)

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🔹 4. Solubility Rules (in water)

1. All nitrates (NO₃⁻), alkali metals (Na⁺, K⁺), and ammonium salts (NH₄⁺) are soluble.

2. Halides (Cl⁻, Br⁻, I⁻) are soluble except Ag⁺, Pb²⁺, Hg₂²⁺.

3. Sulfates (SO₄²⁻) are soluble except Ba²⁺, Pb²⁺, Ca²⁺, Sr²⁺.

4. Carbonates, phosphates, and hydroxides are mostly insoluble (except alkali & ammonium salts).

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🔹 5. Rules for Naming Inorganic Compounds (IUPAC)

Cation is named before anion

Use Roman numerals for variable oxidation states

→ FeCl₂ = Iron(II) chloride

→ FeCl₃ = Iron(III) chloride

In acids:

-ate → -ic acid (e.g. sulfate → sulfuric acid)

-ite → -ous acid (e.g. sulfite → sulfurous acid)

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🔹 6. Le Chatelier's Principle (for Equilibrium)

When a system at equilibrium is disturbed, it shifts to counteract the disturbance.

↑ temperature → favors endothermic direction

↑ pressure → favors side with fewer gas molecules

Adding product → shifts left (reactants); adding reactant → shifts right (products)

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🔹 7. Fajan’s Rule (Polarizing Power)

Predicts ionic vs. covalent character of a compound:

Smaller cation + higher charge = more covalent character

Larger anion = more polarizable = more covalent

🧠 Example: AlCl₃ is more covalent than NaCl

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🔹 8. Color & Magnetism in Transition Metals

Compounds of transition metals are colored due to d–d electron transitions.

Paramagnetic = unpaired electrons

Diamagnetic = all electrons paired

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🔹 9. Werner’s Theory of Coordination Compounds

Metal has two types of valency:

Primary valency (ionizable)

Secondary valency (non-ionizable, coordination number)

Example:

[Co(NH₃)₆]Cl₃ → 3 Cl⁻ = ionizable; 6 NH₃ = ligands (secondary valency)

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🔹 10. Hydrolysi

s Rules for Salts

Salt of strong acid + strong base → neutral

Strong acid + weak base → acidic

Weak acid + strong base → basic

Weak acid + weak base → depends on strength